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April 30

Rust metal quickly.

I'm trying to make a chess set of nuts and bolts, and one side needs to be rusted. How would you rust steel quickly? There is a zinc coating that needs to be removed. I'm thinking of using a strong acid or base to remove it, and I'd prefer not go out and buy it, so are there any good household chemicals that react well with zinc? I can leave it in a safe area, so toxic gases shouldn't be much of a problem. As for rusting the steel, I know that salt water works, but are there any other factors I can manipulate to make it rust faster? Also, should I spritz the solution on or soak it in a bath? Cost is the main worry here, time isn't as important. KyuubiSeal (talk) 00:14, 30 April 2010 (UTC)

If you have some lye, it is a fairly strong base (NaOH) assuming it hasn't been diluted too much. If you have some (applied and pure) chemistry knowledge, you could try battery acid, but that is kind of very dangerous so don't mess with it unless you know what you're doing! The fastest way to oxidize something is to burn it, though the temperatures needed to burn steel probably are outside your price range. 76.229.165.96 (talk) 00:28, 30 April 2010 (UTC)

Dissolve some baking soda in water. Find a power supply (6-18V, do not go higher electrocution hazard). Attach all of your components to the positive electrode of the power supply. Use either stainless steel clips that would not be dissolved, or use junky ones. Attach any piece of metal to the negative electrode. Turn on the power supply. Hydrogen will be emmitted at the negative electrode. If the zinc plating is thick, you will see a white film coming off the positive electrode. After that, ferrous hydroxide (green rust) will be formed. If you let it sit it will be oxidized by air to ferric oxide (brown rust). Let it go for about 10-120 minutes (the higher the voltage, the shorter the time) and take it out. It will be rough and unshiny. If you keep it moist, it should rust in a couple of days. If you want it faster, you can place it in sodium hypochlorite solution to turn it brown. Keep it in there for a day. Remove it and it should be nice and rusty. --Chemicalinterest (talk) 00:30, 30 April 2010 (UTC)

BTW, battery acid isn't very dangerous. If you get some on your skin, you will feel a burning sensation. Quickly pour baking soda on it and wash it thoroughly in water. NaOH is not as dangerous unless it is concentrated (more than 10 molar). It won't dissolve zinc, though. --Chemicalinterest (talk) 00:31, 30 April 2010 (UTC)

So after it forms green rust, does it need to be in contact with air, or can it be left in a bucket of water? KyuubiSeal (talk) 00:39, 30 April 2010 (UTC)

Either. It just needs water vapor, which is present in small quantities in the air, and oxygen, which is present in small quantities in the water, to rust. You could leave it in salt water (probably the fastest), under moist cloths, or in humid air. --Chemicalinterest (talk) 00:47, 30 April 2010 (UTC)

I wonder if you could set up a basic Cathodic protection system and make the parts you want to rust into Sacrificial anodes? The article says they use zinc for sacrificial anodes on steel pipes.. No idea off the top of my head how you'd set it up, you'd need to work out how to attach the components and what kind of current and how to run it, but it might be a fun project if you are into that kind of thing. Vespine (talk) 00:59, 30 April 2010 (UTC)

Yes you could but it wouldn't rust much faster than ordinary corrosion. Ordinary iron contains areas of more stress, which are eaten away and function as anode, and areas of less stress, where oxygen is reduced and functions as cathode. --Chemicalinterest (talk) 11:17, 30 April 2010 (UTC)

Would there be any effects on the glue used to hold the pieces together? KyuubiSeal (talk) 01:49, 30 April 2010 (UTC)

If the glue is made to bond to metal, it might behave differently with the metal oxide. Just experiment on a few before making your set. --Chemicalinterest (talk) 11:17, 30 April 2010 (UTC)

I don't know about the zinc coating, but bleach is very effective at rusting iron and steel. Dragons flight (talk) 01:59, 30 April 2010 (UTC)

Bleach does sounds like a good idea, it is a strong oxidizer, such as Hydrogen peroxide. As for glue, you need a good electrical connection between the components so glue probably isn't the best solution, maybe clamping them between two pieces of steel would work, but the contact surfaces would probably not rust.. Thinking about it, might be more complicated then it is worth, I'd try the bleach idea first. ;) Vespine (talk) 02:17, 30 April 2010 (UTC)

3% hydrogen peroxide rusts too slow. Bleach, as I scientifically called it sodium hypochlorite, does rust iron (and zinc). --Chemicalinterest (talk) 11:17, 30 April 2010 (UTC)

If you want it to rust fast, spray it with water, then dry it on low heat in an oven (as close to, but under 212f). It'll fully rust in no time. I learned that the hard way when foolishly thinking I should quickly dry water from a brake rotor by heating it. To remove zinc I would just sand it. The hotter the metal the faster it rusts. Don't soak it in water - it needs lots of air. Just spray water on it. Ariel. (talk) 06:02, 30 April 2010 (UTC)

Another idea for you: Zinc likes to react with sulfur. Buy some sulfur at a [compounding] drug store (or online), sulfur is pretty cheap. Shake some sulfur all over the metal parts, add ... Actually I'm not sure what the next step would be. I would experiment with heating it, with and without water, and trying to ignite it with a blowtorch. I'm also not sure if the result will stick to the underlying metal. But it should be cheap to experiment. Ariel. (talk) 06:13, 30 April 2010 (UTC)

I tried it, but it didn't affect it. The iron tends to carry heat away too fast. --Chemicalinterest (talk) 11:17, 30 April 2010 (UTC)

right|thumb|Your call Death -what colour!

An easy to obtain acid that will dissolve off zinc and help it to go rusty, is commonly sold in stores as 'Spirit of Salt' better known as hydrochloric acid and used domestically for cleaning drains. When you are ready to make the pieces rusty, use a 10% solution of hydrochloric to remove your 'invisible' but greasy finger prints! That way, you will achieve a more even oxide coat in less time. As mentioned above: a moist warm atmosphere is excellent for rust formation. Be advised though: This form of natural rust is very loose. It will come of as soon as you start playing with them and may make the board feel gritty(you are not the first to think of rusty chest pieces). The acid in sweat and friction will make the metal edges shiny again. It might be better to oxidise the surface to form a Iron(II,III) oxide. This is much more durable. The colour can be adjusted from a grey to a nice black , through brown to a somewhat reddish tone. This coating is often used as a durable finish on military equipment. A professional sculpture would probably choose to send it away and get it done by a sub-contractor. As an example, here is one such firm in Canada.[1]. Another option, very attractive, (only not quite so durable) is Bluing which can be toned all the way down to black. Often used on guns, in order to avoid signalling to the enemy on sunny days “Hay, I 'm over here - hiding in the bushes!”. The bluing solution can be bought from your local gun emporium, for you to do at home. These sort of coating will make it a more practical chess set. After all, you never know who may come to be your opponent !--Aspro (talk) 09:06, 30 April 2010 (UTC)

Yes, if you heat it until it is red-hot, it will form iron(II,III) oxide. --Chemicalinterest (talk) 11:17, 30 April 2010 (UTC)

I'm testing the baking soda bath with a few spare parts right now. I didn't have alligator clips, so I wrapped the copper wire around the screw. Hope the exposed copper doesn't affect it. Hydrogen is bubbling off the negative electrode, and the zinc coating disappeared, so it seems like it's working. Thank you! EDIT: It worked great! KyuubiSeal (talk) 22:40, 30 April 2010 (UTC) If the copper is underwater, blue green copper(II) hydroxide will be formed. If not, it will not have any affect. Do not run it too long or you will completely dissolve the entire screw. --Chemicalinterest (talk) 12:02, 3 May 2010 (UTC)

noble barrier

What is meant by a "noble" barrier, as in a coating to protect iron?--115.178.29.142 (talk) 00:51, 30 April 2010 (UTC)

"Unreactive" or "inert" (like the noble-gas elements). DMacks (talk) 00:57, 30 April 2010 (UTC)

There is a patent covering the idea here. Perhaps that would be of some help? SteveBaker (talk) 00:58, 30 April 2010 (UTC)

It is typically an unreactive oxide coating which prevents further corrosion, such as the one aluminum forms. Another term is passivation. --Chemicalinterest (talk) 01:00, 30 April 2010 (UTC)

Noble gases (like argon) by definition cannot form coatings on metals. Noble metals (like gold or platinum) could be used, though, but they would be prohibitively expensive (although gold coatings are sometimes used on electronic components). FWiW 76.103.104.108 (talk) 07:54, 30 April 2010 (UTC)

Passivation layer may be of interest. Nimur (talk) 15:25, 30 April 2010 (UTC)

Solar sail

How fast would a spaceship propelled by a solar sail go? --75.33.219.230 (talk) 01:34, 30 April 2010 (UTC)

If the sail was powered by a laser, in theory, it could come close to the speed of light. However, to do this, A sail several kilometers across and about 0.001 mm thick would be needed to push a probe the size of the lunar capsule, and micrometeorites would be a major problem. I don't think it's possible. --The High Fin Sperm Whale 02:23, 30 April 2010 (UTC)

Our solar sail article is pertinent, with the first proposal having been to use batteries of Earthbound lasers powered at gigawatt strength for years or decades. I must mention, as always, The Mote in God's Eye as a science fiction novel in which this occurs. Comet Tuttle (talk) 03:13, 30 April 2010 (UTC)

Spaceship propulsion

Would this method for propelling a spaceship work?

1. Uranium is fissioned, releasing energy to power the spaceship.
2. At the same time, an equal amount of anti-uranium is fissioned in a separate chamber, also releasing energy.
3. The two fission chambers are separated by a barrier with holes slightly smaller than a uranium atom. The uranium and anti-uranium atoms can't pass through, but the fission products can, and they annihilate with one another, releasing even more energy to power the spaceship.

In step 3, the same amount of energy is released as if that mass of antimatter had been annihilated immediately, but the preceding fission releases more energy. --75.33.219.230 (talk) 01:34, 30 April 2010 (UTC)

Energy is a conserved quantity. You can't convert a given amount of matter into energy in two different ways and get different amounts of energy. The amount of energy you get by fission will be lost when you collide the fission products, in comparison to colliding the original uranium and anti-uranium. Looie496 (talk) 01:49, 30 April 2010 (UTC)

(ec) I'll leave aside the obvious technical hurdles which prevent such an engine being built, and address what I presume is your central question — do you get more energy out of fissioning the uranium nuclei and then annihilating their fission products than you would from pre-fission annihilation? Instead of giving you the answer outright, I'll ask you a question of my own — Are the products of nuclear fission equal in mass to the original uranium nuclei? Answer that, and you'll be able to answer your question. TenOfAllTrades(talk) 01:54, 30 April 2010 (UTC)

(also ec seems we were on the same page) I'm not a physicist but I suspect that the energy you gain in your fission reaction (and hence the mass you lose) would be the same as the energy you lose by reducing the amount of mass in your matter/anti-matter annihilation. In other words, skip the fission and just annihilate the whole anti-uranium. That's just a guess ;) Vespine (talk) 01:55, 30 April 2010 (UTC)

There are two other points missed by the OP besides the obvious conservation of energy

• Uranium atoms are not smaller than their fission products
• The anti-uranium atoms would annihilate with the container walls.

Dauto (talk) 02:34, 30 April 2010 (UTC)

Ignoring all of the OTHER problems with this scenario, your second problem can be ameliorated with either magnetic or electric fields. For example, if the anti-uranium was ionized, electrically charged walls could repel the anti-uranium atoms... --Jayron32 02:46, 30 April 2010 (UTC)

U-235 + n -> U-236 -> Kr-92 + Ba-141 + 3n

Both sides have a total mass of 236 AMU, so where's the mass loss to correspond with the energy released? --75.33.219.230 (talk) 12:01, 30 April 2010 (UTC)

The AMU is not a sufficiently precise measure of mass here - see binding energy. Gandalf61 (talk) 13:58, 30 April 2010 (UTC)

As gandalf pointed out, you need to be more precise than that. For instance, the mass of Uranium-235 is M²³⁵U=235.0439299 u. Dauto (talk) 14:16, 30 April 2010 (UTC)

OK, here are the values you will need

• M²³⁵U=235.0439299 u
• M¹n=1.0086649156 u
• M⁹²Kr=91.926156 u
• M¹⁴¹Ba=140.914411 u

So, the masses of the left side of your equation add to 236.0526 u and the right side adds to 235.8666 u. Not exactly the same thing.

Dauto (talk) 14:31, 30 April 2010 (UTC)

Using E=mc², we can rearrange the equation to give us an energy-mass equivalence of 9.0 × 10¹³ J/g. Combine that with the value of 0.186 g/mole converted to energy (see above) we get a value of 1.7 x 10¹³ J/mol for the fission of Uranium. In scientific circles, that's what we call a "shitload of energy". --Jayron32 00:39, 1 May 2010 (UTC)

Or put in very basic terms, it's about 200 MeV per atom per fission. Which is enough energy to disturb, say, a bit of dust. Which is pretty impressive for a single atom—I did the mass comparison at some point, and it's along the lines of an ant kicking an ocean liner and having it tip a bit. --Mr.98 (talk) 13:00, 1 May 2010 (UTC)

chrome plating

is there a way to tell if the layer underneath chrome plating is nickel or brass? —Preceding unsigned comment added by Tom12350 (talk • contribs) 02:19, April 30, 2010

Try using a magnet, nickel is magnetic, brass is not. If you have the tools to do it, you can also try measuring the density of the metal. Ariel. (talk) 06:54, 30 April 2010 (UTC)

would the chrome plating interfere with the magnet? —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:29, April 30, 2010

No, chrome is non-magnetic (not under normal conditions, anyway). FWiW 76.103.104.108 (talk) 07:56, 30 April 2010 (UTC)

does it have to be any special type of magnet? —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:44, April 30, 2010

Tom12350, please sign your posts with ~~~~. Just a regular magnet, a stronger one is better I guess. Flexible fridge magnets are pretty weak. Ariel. (talk) 11:48, 30 April 2010 (UTC)

If it is something you do not care about ruining, squirt some concentrated hydrochloric acid on it. If it is nickel, it will slowly fizz hydrogen gas and form a green-blue solution. If it is brass, it will barely fizz at all. --Chemicalinterest (talk) 11:19, 30 April 2010 (UTC)

Even through the chrome coating? Ariel. (talk) 11:48, 30 April 2010 (UTC)

No. --Chemicalinterest (talk) 14:03, 30 April 2010 (UTC)

this item has some greenish rust on it does that tell if it is nickel or brass? —Preceding unsigned comment added by Tom12350 (talk • contribs) 12:18, 30 April 2010 (UTC)

The greenish rust could be patina, not ferrous hydroxide. It would be a copper-containing alloy such as brass, copper, or bronze. Ferrous hydroxide would spontaneously oxidize to brown ferric oxide. --Chemicalinterest (talk) 14:03, 30 April 2010 (UTC)

How to remember names?

I could easily identify people's faces but it's hard for me to remember their names. Any tips on improving name recall?--121.54.2.188 (talk) 07:56, 30 April 2010 (UTC)

Saying their name out-loud whilst looking at them helps. E.g. if someone says "Hello i'm Trevor" you say "Hi trevor" whilst looking at them (similarly if you use their name to start with when referring to them it helps). 194.221.133.226 (talk) 08:15, 30 April 2010 (UTC)

Those that attended the Open University will all know of Tony Buzan. He gave really good advice on how to study effectivly. See Speed Memory – Remembering names and face. Chapter 9 page 59 [2].--Aspro (talk) 09:57, 30 April 2010 (UTC)

How do you learn best? Reading? Hearing? Doing? Whichever it is, do that with the name. Are you good at songs? Make a small ditty out of the name. Or imagine a dance. Or write it down. Or repeat it to yourself a few times. Whichever works best for you. What kinds of things are you good at remembering? Lets say you are good at remembering trees, then in your mind 'link' a kind of tree with the face and then the name. Just think of all three at once. Then you'll see the face, think of the tree, and then think of the name. Ariel. (talk) 11:49, 30 April 2010 (UTC)

I know a teacher, he is amazing with names. I don't know if that's because he's a teacher or that helped him to become a teacher. --Kvasir (talk) 18:35, 30 April 2010 (UTC)

I'm a teacher. I am terrible with names. So it isn't necessarily a related skill. --Jayron32 00:46, 1 May 2010 (UTC)

One thing that works for me is to associate the person with somebody you know who has the same name. Stanstaple (talk) 19:56, 4 May 2010 (UTC)

amines and hydroxide ions

I have reacted amines with hydroxide-sensitive electrophiles quite a few times now, most of the time due to solubility reasons I used an aprotic organic solvent anyway. But funny enough I haven't really thought of this ... if I had water-soluble reactants, if I dissolved bunch of amine (say a good Nu: like a secondary or primary amine) into water with my electrophile (not terribly sensitive to neutral water but sensitive to OH- on paper), would amine or hydroxide have the preference in adding to my electrophile? (Let's say, use a Michael acceptor as a convenient example.) John Riemann Soong (talk) 12:47, 30 April 2010 (UTC)

Can you provide any links where I can understand your terminology? --Chemicalinterest (talk) 16:42, 30 April 2010 (UTC)

Updated! John Riemann Soong (talk) 16:34, 2 May 2010 (UTC)

Our article on ammonium hydroxide notes that only 0.4% of a 1M solution of ammonia in water is in the form of [NH₄]⁺ + [OH]⁻. If this is also the case in the reactions you've been doing, then the concentration of free amine will far exceed that of hydroxide, so [OH]⁻ is unlikely to compete effectively with your intended nucleophile, the amine.

Am I right?

Ben (talk) 12:09, 2 May 2010 (UTC)

Hmm, thanks. Which is a better nucleophile, OH- or NH3? I think OH- is a little better overall, right? Will the comparative effectiveness depend on the mechanism (SN1 versus SN2, etc.)? What about Michael addition? John Riemann Soong (talk) 16:34, 2 May 2010 (UTC)

See nucleophilicity for some quantitative nucleophilicity scales. The rate of reaction of nucleophile and electrophile depends on the identity of both. Hydroxide will react faster with some electrophiles, ammonia (or amines) with others.

Hydroxide should be better at S_N1 than S_N2 because it is a hard nucleophile. NH₃ is (I think) borderline hard/soft, so should be OK at both. Both are bases, hydroxide being the stronger base, so you might get elimination reactions competing with nucleophilic substitution. For example, in S_N1 reactions, the carbocation can undergo E1 elimination to an alkene instead of accepting a nucleophile.

As you probably know, Michael addition favours soft nucleophiles because Michael acceptors are soft electrophiles, dominated by HOMO-LUMO interactions more than electrostatic interactions — basic HSAB theory. S_N2 also prefers soft nucleophiles because the carbon-leaving group σ* orbital is a soft electrophilic centre. I believe S_N1 works with almost any nucleophile, hard or soft, because most carbocations are very strong electrophiles. Where the nucleophile is soft enough and the electrophile can do both, S_N1 and S_N2 will compete.

Ben (talk) 18:38, 3 May 2010 (UTC)

magnetic question

If nickel is magnetic, why is a US 5 cent coin, made of 75% nickel, 25% copper not magnetic? Googlemeister (talk) 14:08, 30 April 2010 (UTC)

An alloy is not "pieces of one metal and pieces of another", but rather a single material with its own material properties not necessarily preserving all electronic and physical properties of each component. Our ferromagnetism article talks about the magnetic issue. DMacks (talk) 14:28, 30 April 2010 (UTC)

You have it backward, it's 75% copper, 25% nickel. Ariel. (talk) 14:28, 30 April 2010 (UTC)

Yes, rare earth metals aren't ferromagnetic, but alloys of them are. --Chemicalinterest (talk) 14:38, 30 April 2010 (UTC)

Neither nickel nor copper are rare earth elements. Every alloy has its own properties; it is invalid to say that "alloys of rare earth metals are ferromagnetic", because it depends on the particular alloy. Every part of you answer is wrong, Chemicalinterest. Please do not make things up before posting them to the reference desk. Nimur (talk) 15:28, 30 April 2010 (UTC)

I did not say that copper and nickel are rare earth metals. I was using that as an example that alloys are sometimes magnetic while the individual metals are not magnetic (or vice versa). Sorry if I confused anyone. --Chemicalinterest (talk) 16:27, 30 April 2010 (UTC)

Samarium-cobalt magnets are very strong, while samarium is nonmagnetic at normal temperatures and cobalt is much weaker. --Chemicalinterest (talk) 16:35, 30 April 2010 (UTC)

If you start adding copper to cobalt, that will start losing its magnetism as well. The copper electron will upset its magnetic moment, just as in nickel.--Aspro (talk) 19:09, 30 April 2010 (UTC)

Why the "niger" in Sciurus niger ?

Hello all,

Not sure if it should go here or on the language desk, but...

I was wondering why the scientific name of the Eastern Fox Squirrel is Sciurus Niger. Niger, both in Latin and in scientific nomenclature usage, has to do with the color black (cf. Niger_(disambiguation)#Species). But the Eastern Fox Squirrel is in fact not black at all, with the exception of some melanistic individuals, as with black panthers). So... why does their scientific name translate as "black squirrels" ?

Thanks, --Alþykkr (talk) 15:55, 30 April 2010 (UTC)

Some names are misnomers. -- Wavelength (talk) 16:26, 30 April 2010 (UTC)

Rattus rattus

This is the sort of question that is bound to come up again. The Type specimen ( the poor critter that ended up picked in a jar and sits on the shelf of some institution) which was used to first describe the species was – black!. As simple as that. Thinking you might not believe such an answer here is a PDF describing Sciurus niger niger.[3] Likewise if you look at the very broad range of Rattus rattus you can probably guess how that came to be the first type specimen as well.--Aspro (talk) 16:43, 30 April 2010 (UTC)

Thanks to you both. Aspro, I had thought of that, but somehow I thought that before naming a species and establishing a "type", you'd take more of a sample than just one individual. Oh well, guess hard sciences are not that hard. --Alþykkr (talk) 17:02, 30 April 2010 (UTC)

I imagine Charles Darwin and others look for a good 'typical' specimen but it's 'that' unique individual, the actual critter in the jar that is the reference specimen that zoologist always return to for comparison. I don't know if anyone can elaborate further on that? If they can, I'll add it to the WP article.--Aspro (talk) 17:13, 30 April 2010 (UTC)

In the 19th century it was pretty much the goal to find the "first" one and get it designated the holotype. Often this led to disputes and later redefinitions (if I recall Harvard has a triceratops skull that they claimed was a holotype, and Yale later proved it was just a variation on an already-identified species—which results in the skull being worth less, having less prestige, etc.). I don't know if that is the case here, but it is not uncommon in that particular era of taxonomy (I don't know if it still is or not, but I would imagine that things like DNA bar coding would make this a bit more unambiguous). --Mr.98 (talk) 02:39, 1 May 2010 (UTC)

transformer

when a transformer is on load its starting current is 12 times of its full load current called inrush current.then what is the starting current of a no load transformer and how. —Preceding unsigned comment added by Dvutukuri (talk • contribs) 16:34, 30 April 2010 (UTC)

The amount of current that passes through the coils of a no load transformer? None on the secondary side. --Chemicalinterest (talk) 16:37, 30 April 2010 (UTC)

Yeah this question is pretty bizarre even by our standards. A transformer typically will inrush some multiple of it's stated max current, like you said (and depending on the transformer's design). If there is no load then ipso facto there is no current on the output, and the input will only draw current according to the inrush characteristics as you already described. --Jmeden2000 (talk) 17:54, 30 April 2010 (UTC)

Per "Protective Relaying" by Blackburn and Domin, page 292-294 if a power utility transformer has no load on the secondary side, then the current drawn by the primary side is called the "exciting current" and its steady state value is typically 2% to 5% of the rated full load current. The transformer core of an unenergized transformer which has previously been energized may have residual flux, either positive or negative. Depending on this residual flux, the point in the voltage waveform at which the winding is energized, and the transformer design, an unloaded transformer might draw little more than the normal exciting current, or it might draw 8 to 30 times the full load current. It is not always 12 times as the OP stated. It may take 10 cycles to one minute for the inrush current on energizing to decay to the steady state exciting current value. In the case of high inrush, the transformer may make a large "Bong!" sound which decreases over a second or so, with dust flying off it. There may be a noticeable voltage dip if it is a very large utility transformer. Protective differential relays may see it as in internal transformer fault and trip the breaker, unless they are properly set to discount harmonic currents. This in itself is pretty "exciting" for those tasked with getting it in service. Edison (talk) 20:39, 30 April 2010 (UTC)

Expansion of the universe

Has it ever been hypothesized that the expansion of the universe is within each subatomic particles' growth from one instant to the next. in other words if you compared an object with mass = X at time = t to that same object with mass = X at time = t + y, it could actually be mass = 2X at time = t (in the past)? —Preceding unsigned comment added by 165.212.189.187 (talk) 16:57, 30 April 2010 (UTC)

No, it hasn't been hypothesized, since it doesn't make sense. If the mass at time t is X, then the mass at time t is X. It can't both be X and 2X (unless it is massless). --Tango (talk) 17:30, 30 April 2010 (UTC)

No let me rephrase: the mass of an object at two different times is two different masses: if you could go back in time and compare the future object to the past object. In other words we are all expanding through spacetime at the exact same rate so relative to each other we are not expanding but relative to our past selves we are. —Preceding unsigned comment added by 165.212.189.187 (talk) 17:45, 30 April 2010 (UTC)

The expansion isn't a mystery that needs to be solved, at least not in the sense you're talking about. It's already perfectly well modeled by general relativity. The idea that physical constants (like masses) might have been different in the past has been tested experimentally in various ways (by looking for variation in atomic spectral lines, for example). The experiments rule out anything more than a minuscule variation in physical constants over the age of the universe. -- BenRG (talk) 18:51, 30 April 2010 (UTC)

Isnt' General relativity is being put to the test everyday with quantum physics?Why couldn't those spectral lines be expanding also? A miniscule variation times all the atoms in the universe equals what ??? And BTW - What, pray tell, exactly is the sense that I am talking about? —Preceding unsigned comment added by 165.212.189.187 (talk) 19:13, 30 April 2010 (UTC)

General relativity makes very good predictions about this on large scales and quantum mechanics makes very good predictions about small scales. It is only when the two situations merge (eg. a large amount of mass in a very small space, like in a black hole or at the big bang) that our theories are inadequate and the expansion of the universe isn't purely within the realms of general relativity. I'm afraid you aren't making any sense at all. --Tango (talk) 21:29, 30 April 2010 (UTC)

I don't recall where I saw it, but there was a comic where a character postulated that he and everything in the universe was about to double in size. The next panels don't show any difference since all the reference points expand as well. If this is the situation the OP is asking about, then it would be an absurd and unfalsifiable proposal that doesn't seem to explain anything. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 21:51, 30 April 2010 (UTC)

It's not a mystery in the sense that we already have a good model. There's always the mystery of "why that model?", but that's different from having no working model in the first place. "Why couldn't those spectral lines be expanding also?" Well, they could, but it turns out (experimentally) that they aren't. I'm talking about spectral lines of distant astronomical objects here, where the light has been in flight for a long time. -- BenRG (talk) 21:50, 30 April 2010 (UTC)

Doesn't seem to explain anything except why the universe is "expanding" . and do spectral lines have mass? Tango says that when the two situations merge that current theories are inadequate and then says that I! don't make any sense?! for all we know those "two situations" are not only merged all around us but completely inseperable! 98.221.254.154 (talk) 04:13, 2 May 2010 (UTC)kgb

So the universe is expanding because the universe is expanding? If the space between atoms is expanding and it's unobservable, then it's something different from the expansion of the universe that we can observe. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 19:20, 4 May 2010 (UTC)

Not the space between atoms, the space INSIDE atoms, between subatomic particles, especially the electron cloud and the nucleus, and empty space itself. we can only observe it on the largest scales. Like when you put a marshmallow in a vacuum canister and it expands. That is whats happening to us and everything else at the same time. like the tidal force of the big bang pulling us in all directions equally.

increase the likelihood of having dreams

I asked a question here about dream recall, and someone suggested that eating lobsters would "increase the likelihood of having dreams". Is this true? What chemicals or substances do lobsters contain that might induce dreams? I must add I have no intention of ever eating lobsters myself because I'm a vegetarian. 82.43.89.71 (talk) 18:15, 30 April 2010 (UTC)

Seems like strange advice. I think that with a good night's sleep the likelihood of having dreams is pretty near 1 anyway. (REM Sleep is certainly almost 100% likely.) It's question of whether or not you remember them. (This usually requires waking up before it ends.) APL (talk) 18:46, 30 April 2010 (UTC)

Some foods, like lobster and cheese-an-onion sandwiches for supper, are 'reported' to give some people nightmares, but there is no proof of this -that I know of. Drugs on the other hand can, so its possible that a meal could send someone's brain messenger chemicals up dramatical. Antidepressants such as SSRI's can definitely give people nightmares and bright vivid dreams, as can St Johns Wort. Generally, I would say that if someone can't remember their dreams, then that is an indication that their brains are working normally. I get the very strong impression at times, from people who can remember their dreams in great detail, that their half way to being loopy – but that's just my impression and not a diagnosis of anyone. --Aspro (talk) 18:54, 30 April 2010 (UTC)

Did you mean to type THEY'RE half way to being loopy ? Cuddlyable3 (talk) 18:50, 1 May 2010 (UTC)

You can get advice about anything here. Sometimes it's worth exactly what we charge. alteripse (talk) 20:59, 30 April 2010 (UTC)

Well, theoretically very heavy meals can put you into a quick, deep sleep (think Thanksgiving - it's the amount of food and alcohol). This is an absurd stretch, but since eating lobster requires more energy than the average meal (cutting, cracking, etc.) and everything is essentially dripped in butter, then I suppose one could make the argument that it's more likely to knock you out than your average other meal. Especially since, lobster being (somewhat of) a delicacy, other things like wine and desert are probably being served as well. ~ Amory (u • t • c) 00:34, 1 May 2010 (UTC)

Quite possibly tryptophan. Cheese contains this, and some page I found on the internet [4] ranks a lot of crustaceans highly for tryptophan content. It ought to just make you relaxed, though, rather than inspire nightmares, as mentioned at Cheese#Effect_on_sleep. There is also cheese syndrome, mentioned at List of foods containing tyramine, and the whole cheese/dimethyltryptamine incompatibility thing, but I guess that has no bearing on lobster. Unless it's fermented lobster. 86.21.204.137 (talk) 11:33, 1 May 2010 (UTC)

It's nothing to do with diet. This probably falls under original research but I once did a course relating to dreams. It seems everyone dreams but many people don't remember them. The thing to do is write down anything you remember, even vague impressions, as soon as you wake up. After a few weeks you will be amazed how much detail you are writing down. It worked for me anyway.--Shantavira|^{feed me} 11:45, 1 May 2010 (UTC)

Jeez - what a lot of terrible answers have been given here! The idea that what you eat causes dreams is pure old-wifes-tale. How about we offer an actual scientific answer with some value to it instead of propagating bullshit?

Vivid dreams happen during REM sleep. As you will notice if you read that article, there has been considerable research into the subject - and not ONE of the linked articles describe evidence for food-related issues with REM sleep. So let's stop talking crap about lobster, onions, tryprophan and cheese - that's complete nonsense.

When you sleep for long enough to achieve REM sleep, you will dream - that's how it works. Typically, you'll enter REM sleep a few times each night - for a total of maybe an hour and a half. However, you won't remember those dreams unless you happen to wake up during REM. So of the half dozen ~15 minute dreams you have every night - you are unlikely to remember most of them. So the only way to remember more dreams (or to even know that they happened) is to somehow be awoken during REM sleep.

However, that's not easy to achieve - if you had something or someone wake you up frequently - you might never enter REM sleep (which would ultimately be bad for your health - people have become mentally deranged from prolonged lack of REM sleep). If you had something wake you up just once at a random time during the night, then the odds are about one in five that it would wake you during REM and produce a dream that you could remember. What you'd really need is someone (or some cunning machine) look for the 'rapid eye movement' that characterizes REM sleep and to wake you up maybe 10 minutes after it starts. However, if you have an alarm clock set to wake you in the morning before you'd naturally wake up by yourself - then that has just as much chance of waking you during REM than at any other time. But because you only spend 20% in REM - waking up with an alarm clock has about a one-in-five chance of waking you in the middle of a dream. But even if you do wake in the middle of a dream - the memory of it usually fades within minutes, so you need to keep a 'dream diary' and make a point of writing down as much of the dream as you can remember, the moment you wake up. So you are almost certainly having several dreams per night - and waking up with the memory of a dream once or twice a week - but simply failing to retain them in long-term memory. SteveBaker (talk) 15:17, 1 May 2010 (UTC)

Tryptophan does send you to sleep, which is a necessary prerequisite for having a dream. My answer may have been terrible and nonsense, but I don't think it was terrible in bold and italics, or complete nonsense. Perhaps lobster gained a reputation by making people more likely to have plesant naps and daydreams at the dinner table, or causing their minds to wander more in the early stages of sleep, possibly followed by waking up again due to indigestion from all the rich food. 86.21.204.137 (talk) 16:10, 1 May 2010 (UTC)

Great - so your advice for dreaming more is to sleep more. Profound. Thanks. Please, at least read REM sleep before you answer any more. SteveBaker (talk) 19:07, 1 May 2010 (UTC)

Your answer was technically correct if you define dreams narrowly, mine was about lobster and I suggested a psychoactive substance in it, and I was quite pleased with myself until you started implying that I'm Mystic Meg or something. I know what REM sleep is. Stop being insulting. 86.21.204.137 (talk) 20:05, 1 May 2010 (UTC)

External stimuli are definitely misinterpreted in dream scenarios. This is dramatised in countless movies where a character is woken out of a dream by a touch or a sound. Indigestion following something one ate the previous evening can also affect one's dream content, usually unpleasantly. This is common experience. BTW SteveBaker, old wives can be reliable sources. Cuddlyable3 (talk) 19:03, 1 May 2010 (UTC)

When old wives write for peer-reviewed scientific journals or other WP:RS...yes. Otherwise, not so much so. SteveBaker (talk) 19:10, 1 May 2010 (UTC)

Would Marie Curie fit the bill? 67.170.215.166 (talk) 05:36, 2 May 2010 (UTC)

Oddly enough, the best answer I can come up with is to get depressed. Antidepressants actually have the opposite effect: they reduce the amount of REM sleep, sometimes to the point of eliminating it altogether. There is a lot of evidence that many people with severe depression have altered sleep patterns that cause them to miss slow-wave sleep and go into the dream state much earlier at night that healthy people do. I doubt that this is the sort of solution the OP was looking for, but it's the only one that comes to me. Looie496 (talk) 23:21, 1 May 2010 (UTC)

Question about gun-type fission weapon

According to gun-type fission weapon the bomb fires U-235 at another U-235 target, and then that achieves critical mass, and fission occurs due to neutrons splitting the atom. Ok, but where are the neutrons coming from? ScienceApe (talk) 19:33, 30 April 2010 (UTC)

Uranium (as with all radioactive elements) is intrinsically unstable and spontaneously undergoes nuclear decay (fission in the case of uranium). So there are constantly neutrons being produced by this natural process. And some of them happen to hit other atoms nearby, causing them to decay. But many/most of them escape without causing anything from happening. In a critical mass, there are enough fissionable atoms nearby that the neutrons from one fission event hit several others rather than generally not hitting anything. The result is an exponential increase in the rate of reaction rather than a constant slow reaction. The "Little Boy" section of the gun-design article you were reading has all this information and more. DMacks (talk) 19:50, 30 April 2010 (UTC)

U-235 and U-238 undergo spontaneous fission with a low probability and this produces a few neutrons (as well as ambient neutrons from other sources like cosmic rays). According to Gun-type fission weapon, the 20% U-238 in Little Boy had 70 spontaneous fission events per second. Once a supercritical mass is assembled, any of these events could trigger a detonation. Dragons flight (talk) 20:00, 30 April 2010 (UTC)

Spontaneous fission is far too unreliable. It was on the article once but I think people are removing things. Around the tops of the uranium pieces were polonium and beryllium rings. When the uranium comes together, the polonium and beryllium are physically intermixed and emit neutrons of about the right energy to initiate a chain reaction and at the right time. There is about a two microsecond window for this to happen.--Aspro (talk) 20:09, 30 April 2010 (UTC)

You could rely on spontaneous fission alone, and Gun-type fission weapon says "An initiator is not strictly necessary for an effective gun design". But in practice Little Boy did use an initiator (that article says "Initiators were only added to Little Boy late in its design), as do implosion bombs. Modulated neutron initiator is the relevant article. -- Finlay McWalter • Talk 20:11, 30 April 2010 (UTC)

In the case of Little Boy, the 20% U-238 in the uranium had 70 spontaneous fissions per second. With the fissional material in a supercritical state, each gave a large probability of detonation: each fission creates on average 2.52 neutrons, which each have a probability of more than 1:2.52 of creating another fission. During the 1.35 ms of supercriticality prior to full assembly, there was a 10% probability of a fission, with somewhat less probability of pre-detonation. Think about it, the figures are naff! They might as well have trained a chimp to bang two lumps together with his hands and it would have been just as 'efective'. This is Wikipedia after all.--Aspro (talk) 20:27, 30 April 2010 (UTC)

I don't know what that means, but see demon core. Comet Tuttle (talk) 22:21, 30 April 2010 (UTC)

If you combined two lumps of the right amount of U-235 in, say, a bucket, you'd definitely get a reaction. But the difference between something carefully controlled and something haphazard would be significant. The first is probably in the neighborhood of 500 tons of TNT (which is still a pretty big explosion by human standards!), whereas the latter is in the neighborhood of 15,000 tons of TNT. If you are really good about controlling it (as they would be in later weapons) you can get more yield from the same amount of material (say, 40kt out of the same original amount), or use less material for the same yield (e.g. you get a "Little Boy" sized explosion out of something that can fit into an artillery shell). --Mr.98 (talk) 23:45, 30 April 2010 (UTC)

Yes, they wanted an overwhelming number of neutrons. The problem is not that a fission reaction would not begin (it would) but that the result would have been a fizzle (if you don't get a very good reaction started, it will blow itself apart before it is really destructive). So they used initiators. Not strictly necessary, but for a totally untested weapon, they provided a pretty good measure of certainty that you'd not only get a reaction, but a big one. --Mr.98 (talk) 23:42, 30 April 2010 (UTC)

the thermodynamics of an ideal air conditioner

Say the temperature of the environment around the exhaust port is at some absolute temperature T3 (it is a heat sink and remains at a constant temperature). You start with room some temperature T2 and cool it to T1.

Under standard atmospheric pressure (constant P and V) of regular old air in the room, how much free energy per mole of air molecules (on average) do I need to expend to effect this temperature change, as a function of the three given temperatures T1, T2 and T3? How would I begin to attack this problem? What thermodynamic relationships should I use?

Some assumptions: heat capacity of air is mostly constant with temperature, especially at the range we're considering (cooling from say, 310K to 290K). And I am curious about the two cases: initial room temperature starts BELOW exhaust temperature, initial room temp == exhaust temp, initial temp > exhaust temp. Btw, the exhaust temp is just the temperature of the heat sink, assume perfect/instaneous heat dissipation from the exhaust to the "outside" so it's not like we have to worry about energy expenditure on fans. And obviously exhaust temperature is always higher than final room temperature (or else the air conditioner would have no purpose -- we'd just go outside!). And of course, assume no heat/mass transfer between the room and the "outside" other than through the air conditioner exhaust.

I'm just curious say, when an air conditioner operates at 1000W, how much of that is used to perform thermodynamic work and how much of that is lost through inefficiency of the machine. How much is also lost due to the inefficiency of the room (on average, assuming a shut door and closed windows)? Rough proportions, of course. John Riemann Soong (talk) 19:52, 30 April 2010 (UTC)

Wikipedia has an article on heat pumps Heat_pump#Efficiency --Aspro (talk) 20:18, 30 April 2010 (UTC)

This seems to be based on the COP definition though. Which is sort of weird. Is there any relation I can get where I can solve for free energy? John Riemann Soong (talk) 22:00, 30 April 2010 (UTC)

Gun with balloon

Attach an inflated balloon to the muzzle of a pistol. Let's say the balloon has a diameter of 20 cm and will burst when its diameter reaches 30 cm. If you shoot the gun, would the balloon be pierced by the bullet or would it burst before that because of the expanding gases from the exploding gun powder? --InfoCan (talk) 20:24, 30 April 2010 (UTC)

After the bullet comes out, the air comes out at the same speed. Probably both will happen at the same time because the bullet and the air are travelling at the same speed. --Chemicalinterest (talk) 20:33, 30 April 2010 (UTC)

The gases will actually decelerate much faster than the bullet will because of fluid drag and turbulence. Furthermore, I am not sure the volume of the expended gases would be enough to pop the balloon by itself. A 20-30 cm diameter increase would represent 1.33*(3.14)*(15*15*15 - 10*10*10) = 522 cc increase, or roughly 1/2 a liter. At STP, this would be .522/22.4 = .0233 mol of expended gas. Even owing to the increase in volume due to the temperature of gas, I am not sure that that much gas is released by the cartridge in the conflagration that expells the bullet. I think its the bullet, and not the gas, that would burst the balloon. If the balloon were exactly at the breaking point, then maybe the gas would break it first. But given the parameters above, I doubt the gas would break the balloon before the bullet would. --Jayron32 21:10, 30 April 2010 (UTC)

Here's my idea: In order for the expanding air to break the balloon, it must first expand from where it is formed (the gunpowder) out to the edge of the balloon. Is it reasonable to assume that the wavefront of the expanding air spreads at the speed of sound? If so, and the bullet moves faster than the speed of sound then it will pierce the balloon before the balloon even feels the force of the expanding air. Thoughts??24.150.18.30 (talk) 02:07, 1 May 2010 (UTC)

Most pistols fire subsonic ammunition (that's a lousy redirect: our ammo article doesn't even talk about subsonic/supersonic bullets. Our cartridge article at least mentions the terms, but only in passing). So the shock wave would hit the rubber first. Would the shock wave to enough to pop a balloon? I have no idea. Buddy431 (talk) 04:57, 1 May 2010 (UTC)

That's because most pistol ammunition actually is supersonic; subsonic ammunition is used in situations where you need less damage potential or you want it to be quieter if the gun itself has a suppressor. The other thing I would point out is that while conventionally you would think that a shock wave in air would travel at the speed of sound, don't forget that the pressure behind the wave is significantly high thus essentially raising the speed of sound for air at that pressure. Given enough pressure the shock wave can easily travel much faster than the speed of sound at sea level. So, to venture a conclusion to the question, there are several variables such as the tension in the balloon (i.e. how much pressure already exists inside it) and the type of bullet and length of gun barrel being used. In most cases I bet that the bullet would puncture the balloon first. --Jmeden2000 (talk) 14:46, 1 May 2010 (UTC)

When the bullet emerges from the muzzle, it is riding in front of a jet of gas molecules produced from the explosion. So the answer to the question lies partly in how quickly the new gas molecules randomize their trajectories and distribute themselves evenly inside the ballon, so as to be able to push the wall of the balloon rather than the back of the bullet. --InfoCan (talk) 04:51, 2 May 2010 (UTC)

Telescope

If we could look far as a billion years light from Earth then why couldn't us look inside in the other planets so we could figure out aliens exist or not. Another question, as i knew if we look at the planet 5 years light ago from Earth what we saw is what happened on the planet 5 years ago not at current time right? Have we prove it?75.168.119.109 (talk) 22:58, 30 April 2010 (UTC)

1. Yes, we can use our telescopes to look at exoplanets circling other stars and try to figure out whether there are advanced alien races living there, probably by looking for a surprisingly large amount of electromagnetic energy coming from the planet (as in the movie Contact). Unfortunately, our telescopes aren't able to resolve sharp detail at many light years' distance, so most exoplanets we have detected so far have been gas giants like Jupiter, which can't sustain life as we know it. As we invent better telescopes, we'll be able to detect smaller and smaller planets around other stars, which may help.

2. That's correct; as our speed of light article discusses, light does not travel instantaneously, but moves at a speed of exactly 299,792,458 meters per second. The term "light year" means "the distance that light travels in a vacuum in 1 year", so, yes, when we look at a star that's 5 light years away from us, we are seeing light that was emitted 5 years ago. The star might have exploded 2 years ago and we're still not going to be able to see that it exploded for another 3 years.

3. Yes, the speed of light has been measured; see speed of light. Comet Tuttle (talk) 23:26, 30 April 2010 (UTC)

Nice answer! But can we look at inside the planets, like look at it's surface? If there are aliens in there, could we see them? Or we only could see the outside of the planets.

It is kind off weird. If we discovered some aliens but they are billion years light from us that's mean those aliens we saw were exist billion years ago, that shows it is hopeless to contact aliens because what we saw is not what actually happening. How far we could look into space, how many billion years light could we look at now? Why don't we invent a big telescope to look at 14 billions years light from us then we could see what happen 14 billion years ago. We may see BIG BANG.75.168.119.109 (talk) 23:53, 30 April 2010 (UTC)

In theory we could see a planet's surface, if we had a powerful enough telescope. However, such a planet probably would not have the atmospheric gases (such as water vapour) Earth does, and would be unlikely to support life. A larger telescope does not necessarily mean more powerful. Furthermore your final assertion assumes that the Big Bang occurred 14 billion light years away, which would put Earth at the edge of the Universe. Intelligentsium 00:01, 1 May 2010 (UTC)

We do not have telescopes powerful enough to show the surface of any exoplanets. But see betelgeuse to see a picture of the surface of a star. Note that betelgeuse is just a few light-years away and still we can barely distinguish any of its surface features at all. The idea of seeing a civilization billions of years away is completely hopeless. The Hubble telescope has allowed us to see pictures of galaxies many billions of years into the past and learn a lot about the beginnings of the universe. Unfortunately, it is not possible to see the big bang because the young universe was opaque. Dauto (talk) 00:13, 1 May 2010 (UTC)

Part of the problem is that light tends to spread out from a source. So, not only do objects which are farther away take longer for the light to reach us; we receive less light from those objects. Now, imagine bouncing a tiny portion of that light off a dark object and trying to catch THAT. Astronomical distances are huge, and relative to stars, planets are pretty small, and in order to support life, planets need to be a considerable distance from stars. In order to improve the resolution of a telescope, you need to collect more photons of light; well, with some of these exoplanets, we may only receive a total of a few photons at a time; far too few to resolve anything. In other words, even if we could catch EVERY photon of light hitting the earth from those planets (a telescope with infinite resolution, lets say) we still could not resolve the surface of the planet to any accuracy. --Jayron32 00:26, 1 May 2010 (UTC)

Most of our telescopes cannot resolve the Apollo landers on the Moon. I doubt that any would be able to resolve surface detail on exoplanets, let alone aliens. ~AH1^(TCU) 01:44, 1 May 2010 (UTC)

We just recently were able to directly see any exoplanet, at all, with any telescope. That's Fomalhaut b. Fomalhaut b is pretty much right in our faces, in star terms, at only 25 light years away. It's a gas giant, probably about the same size as Jupiter, though it's further away from its star than Neptune: that is, it's hard to imagine an alien civilization developing there. However, even with probably the best visible light telescope in the world for this sort of thing (Hubble), it appears to take up about four pixels in the photograph, and no surface detail whatsoever is visible. Now, our resolving power is certainly going to get better with new telescopes; if the Advanced Technology Large-Aperture Space Telescope ever gets built and launched, we might actually get some differentiation across the surface of very near and very large exoplanets. But even that probably couldn't even see a rocky planet closer to its star, let alone resolve surface detail. In short, we aren't going to detect an alien civilization anytime soon by seeing their cities from Earth, regardless of whether they're on the surface of underground. Buddy431 (talk) 04:50, 1 May 2010 (UTC)

I understand the question to be: since we have all kinds of tremendously powerful telescopes, can we look literally inside the planets in our own solar system? That is to say, under the surface of Mars? And I don't know, but I think not. 86.21.204.137 (talk) 11:59, 1 May 2010 (UTC)

Short answer: Yes, we can see below the surface of Mars.

Long answer: It depends on how you define the word "telescope" - but if you think of it as a thing for capturing visible light - then "No" - the solid surface of the planet is opaque to visible light - and you can't see more than a millimeter or two into that kind of object even with a super-bright light source and super-sensitive detector. But if you think more in terms of "radio telescope" and widen your definition of "telescope" to "a thing for capturing electromagnetic radiation" - then you could look at ground penetrating radar as a kind of "telescope"...and we have certainly scanned the surface of Mars with ground penetrating radar (see SHARAD and MARSIS). People don't normally describe these things as "telescopes" because they have to emit the radio waves and read back the reflection from the sub-surface layers of the planet. But this is how we examine the subsurface layers and "look inside" both Earth - and other planets. Obviously though, we can't do that with exoplanets because we have no way to get close enough. SteveBaker (talk) 14:44, 1 May 2010 (UTC)

That's mean our telescope is not advance enough. I think the important thing now is to developed an advance telescope to search for living thing. We only need to see them and take a picture of them. It is easier to contact them than to see them. How many years light could we look from Earth now?75.168.119.109 (talk) 05:38, 2 May 2010 (UTC)

I still don't understand why we could not see the big bang if we could look at 14 billion years light away from Earth, which is the time big bang occurred?75.168.119.109 (talk) 05:44, 2 May 2010 (UTC)

We can't see the big bang because the young universe was hot and dense which made it opaque. So, we cannot see all the way back to the big bang because there is no light coming to us from that far back since it was opaque. That's the same reason why we cannot see the center of the sun. The sun is hot and dense which makes it opaque, therefore there is no light coming to us from the center of the sun. Dauto (talk) 16:48, 2 May 2010 (UTC)

Habeñero pepper safety

Could a healthy person with no underlying medical conditions be hurt by eating an excess of Habeñero peppers? If so, what would be the safe limit for eating them? MMS2013 23:23, 30 April 2010 (UTC)

Capsaicin#Effects_of_dietary_consumption, perhaps. 90.195.179.138 (talk) 23:30, 30 April 2010 (UTC)

Also see Chili pepper#Possible health risks and precautions. Comet Tuttle (talk) 23:32, 30 April 2010 (UTC)

I strongly recommend reading this: http://www.habanero-hamburger.com/index.shtml - it's the website of a recently closed pub in San Mateo who regularly served Habanero Hamburgers - one pepper, lightly grilled, in a regular burger. There are some very detailed - vivid - literally "gut-wrenching" - descriptions about the consequences of eating one of these burgers (and one especially detailed blow-by-blow account here). The consensus is that if you can eat it in 60 seconds and no more than 5 bites - you'll get it down, then be in horrible pain for the next 12 to 20 hours as the stuff makes it's way through your digestive system...and there are many descriptions of "the ring of fire" and "exit wounds"! Having said that, there are people who have eaten them on as many as 20 separate occasions - and others who simply couldn't manage more than a single bite of the stuff. Our local NPR radio station interviewed the owner of the pub just before it closed - he said that he made people sign a waiver and present a doctor's note to prove they had no heart conditions before he would serve them - and despite that had several occasions when people had to be rushed to hospital before finishing their meals! There are a few people who ate two of them at one sitting. So, healthy people can certainly survive eating a couple of these toxic veggies - but it is most certainly not recommended. SteveBaker (talk) 02:10, 1 May 2010 (UTC)

I wonder if Johnny Cash had visited that place when he wrote his hit song "Ring of Fire"... ;-) 76.103.104.108 (talk) 02:27, 1 May 2010 (UTC)

(edit conflict) In college, I had a Hindi-Malaysian roomate who could literally eat them like strawberries. He'd comment that they were very hot, but not unbearably so. I managed to eat one, but didn't relish the experience. Oddly enough, I like the flavor of Habeneros a lot, so long as they are used right. Used sparingly, I find that they have a good "sweet" flavor under the heat, not unlike a Tabasco pepper, I like them better than the milder, but more common, Jalepenos, which I find to be bitter and grassy flavored. --Jayron32 02:39, 1 May 2010 (UTC)

Yes, habaneros are very tasty. I have built up a certain tolerance to the heat, and I agree that they have a lot of flavor beyond the heat. I like to use them to start a tomato sauce (sautee them along with the garlic, before putting in the tomatoes and wine), or sliced thinly on a toasted sandwich of sharp cheddar, black olives, maybe some tomato and avocado. Or I sautee them in the butter that I then use to fry an omelette.

I had to threaten my local supermarket that I'd stop shopping there if they stopped carrying them. They tell me that not many other customers buy them, which seems strange to me — it's not like I'm in the middle of Iowa or something.

There's a pepper I like even better, the Scotch bonnet. I can't find it around here anywhere. It was easily available when I lived in Texas and in Canada. --Trovatore (talk) 09:21, 1 May 2010 (UTC)

An aside here — the pepper's name is simply habanero, no eñe. It means "from Havana" (Havana is La Habana in Spanish; again, no eñe). This is one of my mild peeve spellings, though it doesn't bother me quite as much as latté, which is an error of a similar provenance. --Trovatore (talk) 02:15, 1 May 2010 (UTC)

Just to take the question literal: For most people, "hurt" starts at microscopic amounts of a habanero. "Injured" is much further down that path.... --Stephan Schulz (talk) 09:56, 1 May 2010 (UTC)

I have searched without avail for a BBC news article I read maybe two years ago in which a man died from eating ludicrously hot chilli peppers. What I remember is that they were served to him by a man who grew his own, and either it was a for a dare or there was a mix-up over hotness (perhaps both). What might have happened, of course, is that he turned out to have an allergy; but then you wouldn't think he'd be eating chilli peppers at all. If anybody can find this article, I'd be very grateful, since it's the kind of question that comes up in conversation often. 86.21.204.137 (talk) 12:29, 1 May 2010 (UTC)

If you frequently eat very spicy food, you become insensitive to it. But then normal food will become tasteless. I know someone who cannot eat normal food like bread anymore because of this. Count Iblis (talk) 15:29, 1 May 2010 (UTC)

This is not my experience. I still enjoy non-hot food. It's true that I don't get much satisfaction out of food that's supposed to be hot, but isn't; that strikes me as different from what you're talking about.

My supposition is that the tolerance is specific to the heat-inducing chemical, capsaicin. I can't see any reason that tolerance would reduce your sensitivity to other tastes. --Trovatore (talk) 17:52, 1 May 2010 (UTC)

The stories of people eating these things without the resulting pain reported by others often derives from the fact that there is a huge range of hotness in the same species of pepper. In particular, here in Texas you can buy specially bred 'mild habaneros' that - while still pretty spicy compared to a jalapeno - don't have the gut-wrenching effects of the habaneros at the top end of the scale, yet retain the interesting flavor. I've eaten those - and they don't compare with "the real thing". Our habanero article says that growth environment and and other factors can also have a large effect on the heat of the pepper. The San Mateo pub I linked to above used only Panamanian Habaneros - which are the most notorious kind. SteveBaker (talk) 16:28, 1 May 2010 (UTC)

May 1

Persistent odor

(Note to everyone: This is NOT a request for medical advice)

Just a couple days ago, while testing a sample of refinery wastewater for heavy metals, I accidentally took a whiff of some 5% aqueous ammonia solution (for those who'd never had that happen to them, it feels like a pair of burning matches up your nose). My mucous membranes were burned to a crisp in less than a second, and I had the most horrible itching and sneezing all day long, followed the next day by the worst runny/stuffy nose I've ever had (I've gone through more than two boxes of Kleenex in just one day). All this was stuff that one would expect when one gets ammonia poisoning. What really surprised me, though, was that even after I left the lab, I kept perceiving the stench of ammonia all day long; everything around me -- my hands, my clothes, soap, toothpaste, the food I ate, even the flowers in my yard -- positively reeked of ammonia. (And no, I hadn't spilled any ammonia on myself or my belongings, so the most obvious explanation is out of the question.) Can anyone come up with an explanation for this lingering odor? 76.103.104.108 (talk) 02:45, 1 May 2010 (UTC)

See Sensitization. You could have become rapidly sensitized to the odor of ammonia after your experience. Ammonia is present in LOTS of things. Normally, our brains may not be able to pick the ammonia out of a bunch of compounds that make up the smell profile of something, but given your experience, you may now be hyper-sensistive to ammonia, and can "pick it out" of otherwise complex mixtures of smells, even if it is only present in trace ammounts. Just an idea. --Jayron32 02:52, 1 May 2010 (UTC)

...or you just got a whole lot of it up your nose! 64.69.33.87 (talk) 02:57, 1 May 2010 (UTC)

When you burn your hand, doesn't it kind of feel like you hand is burning constantly until the wound begins to heal? Or when you cut yourself, as if your hand is cut? If there are nerves in your body that know that the smell of ammonia is a hurt smell, I don't see why those nerves wouldn't "throb" after your "injury", thus making you think that you were smelling ammonia. 219.102.220.42 (talk) 03:13, 1 May 2010 (UTC)

Thanks for your answers, everyone. 219 IP, I think your explanation is the most likely, 'cause the smell gradually decreased in intensity through the day, until it finally disappeared the next morning. (And yes, I did get a whole lot of it up my nose, which would explain the intensity and persistence of the smell.) So I can easily see how the nerve endings could continue to tingle for hours afterward, and how this could be perceived as an ammonia smell. As for any possible sensitization, Jayron, maybe I forgot to mention that I've handled ammonia (and smelled it -- it stinks so bad you could smell it from half a mile away) many times in the past -- we use it for a quick-and-dirty test of refinery wastewater for iron, chrome, manganese and vanadium (none of which we're supposed to dump in the river because of toxicity concerns) -- and I've never had a problem until I got a little careless and inhaled the concentrated vapors. Had I become sensitized, it would've happened when I first handled ammonia, wouldn't it? Also, how do you explain the sensitization going away gradually within about 24 hours? 67.170.215.166 (talk) 05:55, 2 May 2010 (UTC)

Sleeping in a chair

I frequently take overnight bus trips and I can never get to sleep on the chair, and I always end up feeling like crap for the rest of the day. Even in bed I can't sleep on my back for some reason, I have to start on my front or else my body never seems to realize that I'm trying to get to sleep. I'm looking for some tips on how to get to sleep sitting in a reclining bus/plane seat, short of taking heavy sleeping pills. I already taken some off-the-counter light pills, but I'm more asking about why I may be having trouble sleeping, and how I can counteract that naturally.

To be honest, I often have the choice to take a bus that will give me two seats, or one that has a fully reclining chair so that I can actually get on my side, but I'm just curious as to why it's so hard for front-sleepers like me to fall asleep on our backs! I guess I also might want to mention that I'm 6'3 (188) so that's also a frequent problem!! 219.102.220.42 (talk) 03:08, 1 May 2010 (UTC)

Part of your answer is sleep hygiene. Much like creating a bedtime routine for children helps them go to sleep, adults often find they need certain 'cues' to get them to sleep. As you say, it is like your body (or brain) doesn't realise you're trying to sleep. People vary in how much this applies to them, but the way you find it easier to sleep is strongly the product of habit. There are also things like sleep apnea, but if you can't even drop off it seems more likely it's just because you don't associate those situations with sleeping. 86.178.225.111 (talk) 16:45, 1 May 2010 (UTC)

Hmmm... practice makes perfect? 210.254.117.185 (talk) 01:27, 2 May 2010 (UTC)

That's actually true when it comes to sleeping in strange places. --Ouro (blah blah) 06:17, 3 May 2010 (UTC)

You need to learn proper relaxation techniques. Let your muscles go slack, your breathing become deeper.. deeper, your body heavier and heavier, you are getting sleepier and sleepier. No?

In a bizarre coincidence, I'm also a 6'3" front-sleeper who has difficulty sleeping on buses and trains. The solution I found was to use a fairly odd sleeping position - put a bag on your lap, cross your arms on it, and sit with your face on your arms. It looks quite silly, but certainly for me it allows me to drop off fairly quickly - i'm apparently enough "on my front" for my brain to decide it's sleep time. Worth a try. ~ mazca ^talk 12:02, 4 May 2010 (UTC)

Yeah, I've done that too on occasion, I'm not sure if I've ever been able to fully fall asleep that way though. A lot of the time though, leaning down on the bus will hit my head against the chair in front! 210.254.117.185 (talk) 21:51, 4 May 2010 (UTC)

Lens-less imaging

I may be misunderstanding some of the fundamentals of optics here, but I was just wondering: if the angle each photon approaches at can be calculated by passing it through a non-focusing surface, would it be possible to resolve an accurate image using those calculations? It seems illogical to me that you could get a "focused" image without a lens, but I don't know why. 219.102.220.42 (talk) 03:36, 1 May 2010 (UTC)

See pinhole camera. Its possible to use diffraction instead of refraction to focus light. Thus, one can make images with tiny holes instead of lenses. --Jayron32 03:58, 1 May 2010 (UTC)

It sounds like you're saying that pinhole cameras work by diffraction. They don't, though you can focus light with a zone plate. -- BenRG (talk) 06:49, 1 May 2010 (UTC)

Sorry, I know what a pinhole camera is, I meant to clump in the pinhole camera with lensed cameras due to the fact it "focuses" the light. I'm asking if it is possible to resolve an image without any directing of the light by calculating the trajectories of individual photons. 210.254.117.185 (talk) 05:28, 1 May 2010 (UTC)

No, photons as particles obey the Heisenberg uncertainty principle, and as such, you cannot know the position AND momentum of a photon simultaneously. In other words, if you can locate a photon's position, you can't tell where it came from before it got there. So it is impossible to assign "trajectories" to photons. Since photons are merely the convenient term we use for the collection of properties that make light kinda-sorta behave like particles, however they are still light; and as such they still obey wave-like properties too, under the right conditions. See Double-slit experiment for a discussion over what happens when you try to assume that a photon is only a particle, and ignore its wave behavior as well. --Jayron32 06:30, 1 May 2010 (UTC)

That's a poor assessment. Heisenberg doesn't say that you can't know them both - it places a limit on the precision with which you can know them both. Since the momentum of the light relates to the color/brightness and the position relates to your ability to focus the image, Heisenberg merely imposes limits on how sharp and color-accurate your photo can be. But that limit is a very tiny one - you can make pretty good photos! SteveBaker (talk) 14:29, 1 May 2010 (UTC)

Photons don't have trajectories; they aren't like the lines of geometric optics. Light is a wave. But you can, in principle, record the electromagnetic field strength at an aperture and computationally simulate the propagation of the light beyond the aperture, through a simulated lens and onto a simulated sensor. Astronomers actually do this at radio frequencies—see Very Long Baseline Interferometry. I don't know whether it's possible at visible frequencies. -- BenRG (talk) 06:49, 1 May 2010 (UTC)

I think the OP is describing something like the compound eye of an insect. There are devices called plenoptic cameras or light-field cameras that attempt to do the same thing. I don't think these cameras are completely lensless, but they chop the light field up into smaller bits rather than passing it all through one humungous lens, which might be what the OP is looking for. --Heron (talk) 09:54, 1 May 2010 (UTC)

Thanks for the answers! I have heard that particles at the quantum level were unpredictable, so that's why I wondered if it would be possible here. In that case I have an expansion to my original question.

Is there any way to make a _surface_ into a camera without using lenses? I specifically want to avoid something like a compound eye, which is really just a lot of small lenses instead of one big one, right? The only way I thought it might be possible is by measuring the photons, but if they can't be measured directly, is there any other way to do this without using a physical lens? I'm thinking of the physical limitations of lenses, in that any camera is only as good as its lens or the corrective measures applied to the lens, but if there were a way to resolve images from sensors, then there wouldn't be this problem. 210.254.117.185 (talk) 10:41, 1 May 2010 (UTC)

No, you can't, actually. The last part of the double slit experiment article discusses this. If you fire photons at a surface individually through the double slits, and let them be detected one at a time, each hitting the detector before the next is fired, you still get an interference pattern; in other words, even if you design an experiment such that light is treated as particle in the most direct way (firing individual photons one at a time) you STILL get wave-like properties. So you can't design a surface which will resolve an image in the way that a lense would, since such a surface would require that the light act solely as a particle. --Jayron32 14:34, 1 May 2010 (UTC)

I recall that the cameras on one of the Mars landers did not have any lenses, and looked slit-like. 92.29.142.124 (talk) 12:22, 1 May 2010 (UTC)

I dunno. According to this, they seem to all have conventional lenses. 210.254.117.185 (talk) 14:30, 1 May 2010 (UTC)

What I was thinking of was static and earlier than the Rovers. Edit: It may have been the earliest lander, when people were concerned about dust storms scouring a lens. Edit2: I was thinking of Viking 1, which shows two slit like things in its photo what may be cameras or imagers. I havnt been able to find anything about these on the internet. 78.151.115.180 (talk) 14:37, 1 May 2010 (UTC)

You should read the papers linked from http://graphics.stanford.edu/projects/lightfield/ - those guys have made a variety of interesting cameras - including a single pixel camera that can take 'normal' photos - a way to transform a photo so you can see it from the perspective of the light source...all sorts of interesting stuff that results from doing numerical analysis of the 'light field'. SteveBaker (talk) 14:29, 1 May 2010 (UTC)

I've heard about those single-pixel cameras - how on earth do they work? 78.151.115.180 (talk) 14:39, 1 May 2010 (UTC)

They slowly scan the thing being photographed, one pixel at a time. The examples I saw take about 15 minutes to take a grainy/blurry photo. -- kainaw™ 14:43, 1 May 2010 (UTC)

Well, you could do it like that - but you'd still need a lens or a pinhole-like aperture - and that's not how the Stanford camera works. Their single pixel camera is an omni-directional detector. What they do is to use 'structured light' - by flashing light on different parts of the scene, the camera builds up a picture from the perspective of the light source. (That's a horrible over-simplification - read their paper to get a more complete answer.) SteveBaker (talk) 16:15, 1 May 2010 (UTC)

Which paper is that please? 92.28.253.63 (talk) 10:56, 3 May 2010 (UTC)

Jayron's answer above is completely wrong. Uncertainty principle applies just the same whether you are using lenses or not. It just turns out that lenses (and mirrors) are the easiest way to disentangle the information contained in the photons into a useful format that allows for an image to form. Dauto (talk) 15:42, 1 May 2010 (UTC)

Yes, exactly. The uncertainty principle imposes strict limits on the ultimate quality of photography - but it says nothing about how you take the photo. Also, the plank constant in the uncertainty principle is a teeny-tiny number! The amount of imprecision that the uncertainty principle causes is utterly negligable in practical photography. What would happen if you tried to take an insanely high resolution image (thereby forcing an accurate position measurement onto the photon) would be that the color and brightness of the image (related to the momentum of the particle) would become less precise. But we're an awful long way from the uncertainty principle imposing limits on the quality of our photography! SteveBaker (talk) 16:15, 1 May 2010 (UTC)

That's not right either. The uncertaity principle does play a role in the optical resolution of a telecope (Assuming high quality lenses). That's in fact the main reason why large telescopes are built. The secondary reason is the increased brightness obtained with larger telescopes. Dauto (talk) 19:36, 1 May 2010 (UTC)

Again, thanks for noting that. I apologize for leading the discussion astray. Of course, we do have surfaces that accurately resolve images without lenses. They are called mirrors. --Jayron32 16:38, 1 May 2010 (UTC)

The uncertainty principle that people have been talking about is already present in classical optics (Maxwell's equations), where it's called the diffraction limit. The classical version of the inequality is Δx Δk ≥ 1/2, where k is the wave number. Quantum mechanically, you can use the de Broglie relation p = ħ k to write it as Δx Δp ≥ ħ/2. Quantization adds shot noise in low-light situations, but aside from that, imaging is governed by Maxwell's equations. When you are limited by shot noise, it does matter how you take the photograph—measurements before and after the light passes through a lens don't commute with each other, meaning that you can't tell from the before-lens measurement what the after-lens result would have been. This problem disappears when the photon count is large because the photons behave as "identically prepared systems" and you can recover complete information about the preparation by doing different measurements on different photons. -- BenRG (talk) 01:06, 2 May 2010 (UTC)

Thanks for the answers and links guys. The digital post-re-focus camera is pretty insane!! So I guess the question is not if images can be resolved from surfaces, but how high resolution they can be. Telescopes are limited by the accuracy of the lenses they use, but the resolution of a surface seems to be restricted by our ability to resolve the properties of photons. I imagined a very long, thin tube with the "sensor" surface on the inside of it, in order to block all the photons from outside of a small patch of sky, but I imagine the wave properties of light will make it impossible to create an image of anything too small/far away. Thanks again! 210.254.117.185 (talk) 01:24, 2 May 2010 (UTC)

If I'm not mistaken, taking a photo by measuring the angle, and without using a lens, is exactly what a hologram does. Ariel. (talk) 02:52, 2 May 2010 (UTC)

Titration curve: part 2

My question is very similar to the one I asked earlier, but it's different enough that I thought I should ask separately.

If I have HCl of a known concentration & volume, being titrated with NaOH of known concentration, and I add x mL of NaOH. How do I determine the exact relationship between pH and x, with no approximations whatsoever? I know that I can use Jayron's method for pH's close to 7 and conventional methods for pH's far from 7, then combine the 3 resulting functions into one, but I can't help but think there has to be an exact mathematical formula for the titration curve. --99.237.234.104 (talk) 04:45, 1 May 2010 (UTC)

You can always use an ICE table. First, react the two species to completion. Then, use those values as the Initial values in the ICE table. This will give you the relationship Kw=([H+]initial + x)([OH-]initial + x). Solve the quadratic equation for x, add that x value to the initial H⁺ concentration, and take the negative log. Note, though, that there are surely some error bars on your amounts of H⁺ and OH^-, so there's little use in getting an "exact" value in this way unless you have very close to equal amounts of acid and base. Buddy431 (talk) 05:31, 1 May 2010 (UTC)

Dry nose when sleeping upright

If I fall asleep during the day, in an upright posture, for instance while sitting on a train or at a desk, I invariably awaken with a very dried-out nose. This never happens if I fall asleep lying down. Why might this be the case? 129.174.184.114 (talk) 06:31, 1 May 2010 (UTC)

I didn't know humans had wet noses. Are you a dog? --TammyMoet (talk) 09:14, 1 May 2010 (UTC)

We do have healthy wet noses, on the inside. This came up on this very desk a month ago, in a question titled "juicy nose". 86.21.204.137 (talk) 12:21, 1 May 2010 (UTC)

I am rather certain that the response then was the same as now: We cannot diagnose how a questioner's nose works without physically inspecting the questioner. -- kainaw™ 14:44, 1 May 2010 (UTC)

Why are people whispering? — Knowledge Seeker দ 17:48, 1 May 2010 (UTC)

You are breathing through your nose and too fast. Try breathing more slowly or prop your mouth open. This will then give you a dry mouth instead.--79.76.230.67 (talk) 21:42, 3 May 2010 (UTC)

name of shooting device

i saw this

http://www.youtube.com/watch?v=fRLCh0Re_LA&feature=PlayList&p=2CA7AB94E58204FB&playnext_from=PL&index=0

what is the name of the shooting device he is using? not the gun but the device that the gun is attached to that makes it have no recoil. its not called a bench rest because thats something else. i want to buy one and need to tell the gun store exactly what im talking about —Preceding unsigned comment added by Tom12350 (talk • contribs) 10:49, 1 May 2010 (UTC)

Please don't post the same question on more than one desk. There is a recoil on the gun, it goes back about two inches. Finally I imagine your gun store has access to You-Tube and can view the vid for themselves. Caesar's Daddy (talk) 13:43, 1 May 2010 (UTC)

The page that video comes from is here, which suggests it's part of a benchrest shooting setup. The Wikipedia article claims that most benchrest shooting setups are custom made. -- Finlay McWalter • Talk 13:57, 1 May 2010 (UTC)

Physics

Hi, please help with these two questions:

1. Estimate what's the difference between cp and cv of chosen metal. (Instruction: Find the temperature coefficient!)
2. Does specific heat of metal have constant value or does it depend on temperature interval? —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 13:09, 1 May 2010 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

Try reading specific heat the answer to half of your problem is right there in the introduction. SteveBaker (talk) 14:13, 1 May 2010 (UTC)

I tried really hard to solve this problem, but all i could do is this: 1. Table of specific heat capacities: it's written that the cp of copper is 0.385 J/(g·K) and cv is 3.45 J/(cm3·K). I just don't understand how to compare them as they have different unities (J/(g·K) and J/(cm3·K)) and what does the temperature coefficient have to do with it? 2. "These quantities are "intensive quantities", meaning they are no longer dependent on amount of material, but capture more directly the dependence on the type of material, as well as the physical conditions of heating."----> So specific heat capacity doesn't depend on mass but it depends on the temperature interval? Actually I had to do 6 pages but this was too tough... —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 19:09, 1 May 2010 (UTC)

Why would it depend on the interval? Dauto (talk) 21:57, 1 May 2010 (UTC)

Relations between heat capacities might help a little, but honestly you're going to get the best answer for this class by looking at the text and notes you got for this specific class. For example, I know that specific heats of metals do vary with temperature, but rarely enough for it to be an issue for most calculations you'll be doing. Therefore, your class might be expected to say "No, it's constant and doesn't vary with temperature", because that's what you are supposed to assume. But equally, your class might be expected to say "It varies, and here's a table of how the specific heat of ____ varies with temperature". Without being in your class, we can't tell what answer you're expected to learn. 86.178.225.111 (talk) 00:17, 2 May 2010 (UTC)

We could help by pointing out that the unit for Cp is Joules per (gram * degree Kelvin) and for Cv is Joules per (cubic centimtre * degree Kelvin) - so to compare them, all that's needed is to find out how much a cubic centimetre of copper weighs. --Phil Holmes (talk) 09:50, 2 May 2010 (UTC)

Excitation of an atom

Can a an atom in the excited state jump to another higher state when a photon is incident on it? —Preceding unsigned comment added by Rohit.bastian (talk • contribs) 14:26, 1 May 2010 (UTC)

DO you mean the atom itself or do you mean the electrons of an atom? --Jayron32 15:01, 1 May 2010 (UTC)

The answer is yes. Jayron, that's nit picking... Dauto (talk) 15:47, 1 May 2010 (UTC)

He and his brother are in a higher state. Amen. Cuddlyable3 (talk) 16:44, 1 May 2010 (UTC)

Certainly. That's how we get Balmer lines in absorption, amongst many other things. Modest Genius ^talk 20:28, 2 May 2010 (UTC)

Measuring general radio/tv/phone wave strength

For an elementary school science project that is testing how terrain and weather affect wireless communications, what is the best way to measure the "strength" of radio/tv/phone waves? I figure that it will require an extremely wide-band antenna. What circuit could be used to get a general measure of strength (voltage, amperage, whatever)? Can this be completed by elementary school students or is the construction far too difficult? -- kainaw™ 14:31, 1 May 2010 (UTC)

A simple AM receiver can be built using instructions in just about any hobby electronics kit. It doesn't even have to be an amplified circuit. An unpowered AM receiver circuit will pick up radio waves just fine; the early experiments in radio broadcasting used unamplified circuitry. An unamplified circuit would make it easier to quantify the strength of the received signal. You could likely detect the strength of the received signal by hooking the leads from the receiver to a multimeter RATHER than a speaker. History_of_radio#Wireless_experiments_of_the_19th_century discusses some of these experiments. I have seen demonstrations of David E. Hughes's experiments using stuff you can get at a hardware store. At the most basic level, you can demonstrate radio using a speaker and a decently strong spark, without so much as an antenna or receiver circuit. This article at Howstuffworks.com actually contains some pretty good stuff on radio, how it works, and how to build simple transmitters and receivers at home using basic materials. The section titled "The Simplest AM Receiver" shows you how simple such a receiver can be. --Jayron32 15:40, 1 May 2010 (UTC)

Many Mobile phones and PC's equipped for Wireless LAN can display a crude scale of signal strength so no construction is needed to use them. An unamplified Crystal radio will not separate stations well, the voltage you could measure at the output is dc plus large ac variations, and the size of antenna required does not lend itself to portability. An easier choice is a cheap Transistor radio of an older design using discrete components. You can connect a voltmeter to the internal AGC line and the reading will be a (rather non-linear) indication of received signal strength. In principle you could do the same with a car radio but they are harder to open up. However professional equipment is needed to take calibrated measurements over a wide frequency range. Running a Spark-gap transmitter will get you into trouble you can do without.Cuddlyable3 (talk) 16:37, 1 May 2010 (UTC)

I was planning to use old radios, but the goal is to measure as much of the signals out there as possible all at once. There isn't much. There are no local television stations, one FM radio station that sometimes comes in, two AM radio stations, only one cell tower (owned by Verizon), and tons of CB radios. I figured that if necessary, we could measure the strength of the FM station since it fluctuates regularly, but I was hoping to get a better set of reliable data by trying to measure everything that is out there all at once. -- kainaw™ 18:05, 1 May 2010 (UTC)

The trick to making a great science project is not about the equipment - it's about the methodology. I think, in your position, I'd take my cellphone and a paper map of the area. Find out where the cell towers are and pick a suitably large area with hills and other terrain which you have free access to. Then walk around the area methodically writing down the number of bars you're getting on your phone every 100 meters (or whatever). If you can borrow a handheld GPS - or if your phone has GPS, you can get your position from that. If you get it right, you should end up with a map covered with numbers. Now you can look at the contour lines on the map and the locations of the towers and color the map with regions where you got 0, 1, 2, 3, 4 or 5 bars. When you do this, try to hold the phone in the same orientation each time - try to do all of your testing in similar weather condition.

Once you have data - try to form some results - does the number of bars depend on the distance from the cell tower? Do intervening hills make a difference? Did you need to be able to see the tower to get a good signal? Can you form a hypothesis from this data? Perhaps you could test your hypothesis by finding a different area with a different cell tower and predict where you think you'll get good reception and where bad. Then test your hypothesis by actually going to those places and seeing if you get the number of bars you predicted.

SteveBaker (talk) 18:42, 1 May 2010 (UTC)

If you have a budget, you can buy a HAM base (or a standalone receiver) and a VU meter. A VU-meter runs you anywhere from $5 to several hundred dollars (depending on accuracy, digital/software features, etc). Depending on the number of bands you care about, a receiver can run anywhere from $200 to several thousand dollars; at a certain point, you buckle down and buy a mixer too, to expand the frequency capabilities of your receiver. This transceiver unit costs a lot, $2000, but includes a neighborhood spectrum analyzer; or you can use a cheaper but less-interesting Wattmeter display. It operates from 500 kHz to 54 MHz, so if you want to go up to VHF (to listen in on television, commercial radio, and so on), you need to buy a good mixer. Unfortunately, this gear is expensive, technically difficult to use, and requires at least intermediate understanding of radio theory (specifically, how frequencies add when you mix and modulate). The good news is, in receive-only mode, you could train your students to dial in each frequency and record the measured signal level fairly "cook-book"-style. This is really the only way you can sweep out ALL frequencies and get a raw power measurement. If you want to restrict yourself to just a few commercially-used frequencies, such as detecting quality of reception from a commercial AM/FM/UHF/VHF/digital-broadcast television station, your best bet might be to hack up a voltmeter to the inside of a commercial radio or television. Two problems with this: so much stuff is done with an integrated circuit, it might be impossible to locate a place to connect your voltmeter probes. Secondly, so many of these systems have so much signal conditioning, including gain control, that it will be hard to decipher what the actual received radio power is. Nimur (talk) 20:37, 1 May 2010 (UTC)

Boiling

why did water or any liquid comes up when boiled.? —Preceding unsigned comment added by Legend killer harshit (talk • contribs) 14:32, 1 May 2010 (UTC)

The gas form is less dense than the liquid form, so it rises. -- kainaw™ 14:34, 1 May 2010 (UTC)

As the water (or whatever) boils, it turns from a liquid into a gas. If you boil a certain amount of water, the resulting gas (steam) takes up about 800 times more space than the water did. Steam is 800 times lighter than water - so the bubbles formed in the liquid rush to the surface and escape into the air - but between forming and reaching the surface - they take up more space. The combined effect of all of those expanding bubbles forces the level of the liquid in the container to expand.

The answer is actually a little bit more complicated than that. When you boil ordinary tap water, the dissolved air in the water actually comes out of solution at a lower temperature than when the water boils - so you do get small bubbles forming before the water gets hot enough to boil. Those bubbles also increase the volume of the water by a small amount - so the volume of the water starts to increase a little before it actually boils. But the biggest expansion happens (as you say) when the water hits boiling point. SteveBaker (talk) 15:43, 1 May 2010 (UTC)

Question - Helium Canister

Why don't helium canisters float away? —Preceding unsigned comment added by Taratrapie (talk • contribs) 14:56, 1 May 2010 (UTC)

1. The helium is compressed, and so more dense than the air around the canister. 2. The canister is more dense (i.e. has more mass per unit volume) than the air around the canister. This being the case, the canister fails to displace sufficient air to equal its weight, and so sits there unmoved. --Tagishsimon (talk) 15:02, 1 May 2010 (UTC)

In otherwords, the heavy metal that the canister is made out of compensates for the boyant force of the helium given that it is lighter than air. In order to float, the entire container must be lighter than the a chunk of air the same size as the container. For a relatively light and thin balloon, this works. For the heavy metal container, it doesn't. However, if you place a full helium cansiter on a scale, it WILL weigh less than an empty helium canister. --Jayron32 15:15, 1 May 2010 (UTC)

Jayron's answer is incorrect. Remember - the helium is under pressure. Helium is about 7 times lighter than air at the same temperature and pressure. But if you put just 8 cubic feet of helium into a 1 cubic foot tank - then the tank would be heavier than it was when it was full of air. Bottled gas says that a typical gas tank is pressurised to 200 to 400 times atmospheric pressure - so helium at that pressure is between about 30 to 60 times denser than atmospheric-pressure air - so a fully pressurized helium tank will be considerably heavier than an empty one. The tank would have to be about 97% to 99% empty before it would start to weigh less than a tankful of air. SteveBaker (talk) 15:35, 1 May 2010 (UTC)

Correct, of course. (chances are, you can safely ignore any answer I ever give. I am wrong more often than I am right). What I should have said was that a canister of helium would weigh less than a canister of air filled to the same pressure. That would have been correct. What I said above was total bullshit. Just ignore me. --Jayron32 16:00, 1 May 2010 (UTC)

Proving references to back up claims not only helps others find more information on the subject by following the links, but also makes sure what you say is always (or as near as can be) correct :) 82.43.89.71 (talk) 19:20, 1 May 2010 (UTC)

Sky

I was looking at the sky today and then I thought about how the earth is spinning through space at amazing speeds. Why don't the clouds be affected by the spinning of the earth? Or is this exactly how the wind is made? —Preceding unsigned comment added by Goei--inkso (talk • contribs) 15:05, 1 May 2010 (UTC)

One way of thinking about this is to consider that air - gases - have friction. And space has a frictionless vacuum. If an atmosphere of gas is held around a planet by gravity, as our atmosphere is, then it is certain to take more notice of the spin of the glove it is attached to, through the mechanism of friction, than it is to be influenced by the vacuum of space. I'll leave you to read Wind#Cause for more on that subject. --Tagishsimon (talk) 15:08, 1 May 2010 (UTC)

The clouds ARE affected by the spinning of the earth. See Coriolis_effect#Meteorology. The fact that the earth is spinning effects the general path clouds take as they move across the earth. You don't see this standing under them because of the scales involved, but if you watch animations of weather patterns, such spinning effects become clearly visible. --Jayron32 15:13, 1 May 2010 (UTC)

Indeed. And this is explained at Wind#Cause. Sigh. --Tagishsimon (talk) 15:39, 1 May 2010 (UTC)

Modern crystal radio

Would a modern crystal radio with an earpiece be useable for recieving long-wave, medium-wave, or FM broadcasts in the UK? 78.151.115.180 (talk) 16:38, 1 May 2010 (UTC)

I don't know how usable it would be, as you need to be in a silent room to hear anything. StuRat (talk) 16:43, 1 May 2010 (UTC)

(edit conflict)Sort of. The problem with crystal radio is that it is an unamplified circuit, so it needs a pretty strong source. It also cannot directly decode an FM signal, which requires something more advanced than a diode to resolve the signal. However, in principle they can resolve any AM signal, regardless of the wavelength of the source, without any modification. They can resolve FM signals using slope detection, i.e. since FM signals also display AM properties at the boundaries of the bandwidth of the signal, you can "fudge" it by tuning an AM tuner to those boundaries. It produces a noisy, inferior signal, but it can be done. --Jayron32 16:46, 1 May 2010 (UTC)

BBC world service on 648 KHz has a very powerful signal that can easily be picked up with a crystal radio all over Western Europe. This signal so strong that the lack of selectivity of the crystal radio will make it difficult to hear weaker stations like radio Five Live on 693 KHz. Count Iblis (talk) 17:06, 1 May 2010 (UTC)

Thanks. Is there a list anywhere of the wattage of different radio stations, or even what their signal strength may be in various places in the UK? A minature crystal set pernamently tuned to the World Service would not be a bad thing. 89.242.97.110 (talk) 11:09, 2 May 2010 (UTC)

Why do we forget our dreams?

Is it known why, if we don't actively try to remember our dreams as soon as we are awake, we will forget our dreams, even though they might seem vivid just moments ago? --98.114.146.35 (talk) 19:40, 1 May 2010 (UTC)

Its probably not a bad thing to forget your dreams; you have a limited (very large, but still techinically finite) amount of storage capacity in your brain, it makes sense to fill it with stuff that you need on a regular basis (like people's names, how to do stuff, whether or not you left the oven on, where exactly was that bear's den? What was my wife's birthday? etc. etc.), versus dreams, which are pretty much useless when awake (as much as I would like to savor that night I spent with Brooklyn Decker...) That your mind sort-of-automatically knows which stuff to file away as "important" and which stuff to discard is pretty cool. Lucid_dream#Dream_recall and Dream#Recalling_dreams contains some methods for training yourself to remember dreams (caveat emptor, YMMV, etc.). --Jayron32 20:32, 1 May 2010 (UTC)

It is not known why that happens at the physiological level, but I'll tell you my hypothesis. The storage of memory in the brain is thought to depend on a mechanism called long-term potentiation (LTP), which we know quite a bit about. One of the things we know about LTP is that it takes place in two phases. The first phase produces a memory trace that lasts for a few minutes. The second phase, which is dependent on protein synthesis, produces a trace that lasts for hours or longer. My hypothesis is that during the REM sleep stage (when dreams occur) there is an alteration in brain chemistry that disables the second phase of LTP. In order to make a dream memorable it is usually necessary to think about it very soon after waking, before the temporary trace has disappeared bu after awakening has re-enabled the long phase of LTP. I don't know of anything in the literature that contradicts this explanation; but I don't know of anything that proves it is correct either. Looie496 (talk) 23:11, 1 May 2010 (UTC)

This is WP:OR - but I have a compelling hypothesis for dreaming that fits all of the available facts. It appears to me that the brain is doing something akin to 'defragging' the disk drive on your PC. It's rearranging memories for greater efficiency.

If we pursue this 'defragging' analogy, what happens in your computer is that the PC moves blocks of data off of the hard drive, into RAM and then writes them back out to the hard drive in a more "logical" position. Block by block, it rearranges the files on the disk into a more streamlined arrangement that allows the computer to get at the blocks that make up the file very quickly. It used to be the case that you had to make sure that you weren't running any programs at the time you did this - but modern PC's now allow that.

This analogy isn't backed up by much evidence - but it fits the facts perfectly - and is very compelling:

• Dreams (or at least "REM sleep") is very important to us. We can do without it for a while - but if we don't get enough REM sleep over an extended period of time, we get slower, stupider, and ultimately: seriously mentally deranged! If your PC isn't defragged, the files gradually get more and more chopped up and spread all over the disk, like shuffling a deck of cards. Getting at those files starts to take more and more time. Defragging streamlines all of that - puts all the bits of a particular file next to each other...like sorting a deck of cards.

• Our bodies are 'cut off' during REM sleep so we don't 'act out' our dreams while the data is being moved around. This is a good fit for the old "don't run programs while defragging" rule because your software would see temporarily screwed up files while they were being rearranged. Less intelligent animals (dogs, for example) haven't quite mastered this - and when they dream, you can see their feet twitching like they are running - and there are little barks and such. We only move our eyes around under the eyelids.

• If you don't wake up - then the result is that your memories are streamlined and more efficiently accessible - you wake up feeling more alert and refreshed. You don't remember this rearrangement of memories because everything was 'turned off' while they were being moved around.

• If you do wake up - then it's like you stopped the computer midway through 'defragging'. What's in the computer's RAM memory when you do that is just a random collection of bits and pieces of different files you have on the disk. This fits perfectly with the human experience - your short term memory ("RAM") is full of random bits of real long-term memories that were in the process of being re-organized at the moment you wake up.

• If you wake up during a particular dream (and therefore stand a chance of remembering it) - then that section of your memory hasn't been properly 'defragged'. The next time you sleep, the brain has to go back and try to sort that bit out again. If you wake up again, the same stuff is in your short-term memory the next time - and it seems like you had a 'recurring dream'.

But in this hypothesis, your memory doesn't ever contain any kind of "story" - the dream wasn't like a movie playing in your head. It was just random bits of memories, put together in any old order. When you wake up, your short term memory ought to be empty - but it's full of random bits of memories. What is your conscious mind supposed to do with a bunch of completely random bits of old memories that are packed into short term memory just as if they had just happened? That's easy - we think they were true short-term memories - things that just happened to us. We try to put these into a sensible sequence of actions - but it's difficult because it's basically a mess. The brain doesn't put these 'stories' we invent at the moment of waking up into long-term memory unless we specifically concentrate on doing that (eg by writing them down) - so the stories disappear as soon as short term memory expires.

In this hypothesis, the dream didn't actually "happen" at all - it's a bunch of old memories that seem to have just happened if we happen to stop the memory reorganization right in the middle. If that hypothesis is true (and it seems entirely reasonable) - then the issue of 'remembering' wouldn't come up. A dream isn't like a story or a movie unless we wake up while the REM phase is happening. You don't "forget" your dreams - you simply never remembered them in the first place...the dream literally didn't happen unless we woke up.

From what little we know of how memories are stored - there isn't enough storage space for all of our memories to be retained in full detail for life. We forget things that aren't important, we simplify memories where detail is unimportant - some process in the brain must be doing that reorganization on a daily basis - and REM sleep fits the bill perfectly.

I must emphasize that I know of no evidence that this hypothesis is true - but as far as I can tell, it fits all of the facts perfectly. SteveBaker (talk) —Preceding undated comment added 00:47, 2 May 2010 (UTC).

Nice theory, but it doesn't seem to fit with the phenomenon of lucid dreaming. It is possible to realise you are dreaming and take control of the dream - that couldn't happen if the dream never actually happened. --Tango (talk) 00:56, 2 May 2010 (UTC)

Having read Feynman's account of lucid dreaming - I'm inclined to the view that lucid dreams are not REM sleep. He found that when he engaged in this activity, he lost all of the benefits of sleep and he consciously decided not to pursue it because he was concerned for his intellect and state of mental health. That actually fits what I believe. The idea that the brain starts to defrag things - then the conscious mind steps in and starts directing a 'story' (albeit when still "asleep") simply disrupts the memory re-org that's in progress and turns things over to conscious thought. In effect, lucid dreaming isn't the same thing at all. SteveBaker (talk) 13:36, 2 May 2010 (UTC)

Steve's theory has a lot in common with the theory proposed by Francis Crick and Graham Mitchison in 1983, see PMID 6866101. (You can find a pdf online using Google Scholar if you want one.) There isn't a lot of evidence to support it though. There is lots of evidence relating sleep to cleanup of memory, but it mostly points to slow wave sleep rather than dream sleep. Gulio Tononi, in fact, has been pushing a sort of "defragging theory" of the function of slow wave sleep for the past few years, in papers such as PMID 16376591. Also, most sleep researchers favor the idea that dreams play out in real time rather than being stitched together ad hoc on waking. The evidence is somewhat sketchy, mainly involving studies relating eye movements during dreams to the experienced events reported on waking, but it does seem to trend in that direction. Looie496 (talk) 01:08, 2 May 2010 (UTC)

Well, like I said - it's just a hypothesis. The sketchy nature of dream recall seems to me to make correlation with eye movement during REM an 'iffy' piece of evidence at best...but I'm no dream researcher! I originally trained as a cyberneticist (that's what my degree is in) - and cybernetics is all about looking for ways to compare what happens in biological situations and in robotics and computing - so it seems natural to me to look for these kinds of analogies as ways to suggest answers to things that are tough to study in the brain. Sometimes it produces useful insights - sometimes not.

The 'real time' nature of some dreams is certainly a problem for my hypothesis - and it's evident in watching dogs sleep - they seem to lack some of the ability we have to 'turn off' motor control during REM. This gives us a handy way to observe dreams playing out - but unfortunately, not in human subjects. So you see their feet twitching, first one by one like they were walking, then all four together, like they were running, then you hear tiny little barks and sometimes chewing motion with drooling. That's certainly compelling evidence for a real-time dream of squirrel chasing, catching and devouring...but these motions are not long enough to account for the length of dreams that I recall. The entire dog-dream seems to last under a minute - but the evidence (see REM sleep) is that REM lasts for 15 to 20 minutes at a stetch.

So I imagine that what we're seeing is either the recall or the storing of one of the snippets of a memory being pulled into short-term memory in preparation for putting back into long term memory in a different form. The idea that short bits of actual memory have to be replayed in realtime as they are re-organized isn't such a strange idea. After all, the ability to do this stuff had to evolve somehow - and perhaps the ability to re-record short term memory back into long-term requires the memory to be replayed in something like realtime. So this problem isn't necessarily devastating for my hypothesis.

Also, it couldn't be that REM sleep was the whole picture - otherwise, presumably, we'd sleep for only one to two hours a night and have just REM sleep and nothing else. So there are any number of other possibilities. One is that 'long-wave' sleep is a planning process where the brain figures out what needs to be reorganized - and REM is the actual reorganization. That would neatly explain the alternation between the two kinds of sleep. It might also be that long-wave sleep does contain 'real-time dreams' but that the process of erasing all memory of them actually works OK if we're woken up in the middle of them. The fact that dream recall only happens if you wake up during REM (or very shortly afterwards) might well be a failure of the "forget it - it's only a dream" mechanism - or (more likely, IMHO) that REM leaves this 'junk' in our short term memories and we need enough time after that to allow short-term memory to naturally fade away.

The problem I have with other theories is the question of why we dream at all? It's clearly a costly process (in terms of all of this brain activity consuming energy) - and it's clearly essential to our mental health (if you don't dream - you get into a lot of trouble) - so it must have evolved for some rather critical reason. We know that other mammals have 'REM sleep' with dreams (certainly dogs and cats do) - so we can say for sure that it evolved long before big-brained humans needed it. Without the need to dream, why sleep at all? Sleep is pretty dangerous from a perspective of being vulnerable to predators and such like - so it must have a rather massive benefit or we'd evolve to not do it. We know that birds sleep - so the evolution of sleep must go back at least as far as the split between mammals and reptiles - so dinosaurs must have slept. We even know that some birds, whales and dolphins sleep with only one hemisphere of their brains at a time in order that they can stay conscious 24 hours a day. So this is clearly a vitally important bit of what makes brains tick.

The 'defragging' idea seems to be the only idea I've come across that has a compelling explanation of the need for sleep and why we feel so terrible when we don't get it. Arguments that we have to 'rest our bodies' are patently untrue. If I lay still in bed, reading a book all night - I still feel crap in the morning. My body got all the rest it needed - but my brain didn't get to defrag. SteveBaker (talk) 13:36, 2 May 2010 (UTC)

Difficulty remembering dreams is very useful to help you keep track of what really happened and what happened in a dream. If we remembered our dreams perfectly, we wouldn't know if they had actually happened or not. --Tango (talk) 00:56, 2 May 2010 (UTC)

During a dream, our waking sense of logic is often hindered or corrupted. When we wake and logic is slowly restored, the context of the dream may no longer be realistic, rendering the details of the dream as conceptual gibberish. ~AH1^(TCU) 01:10, 2 May 2010 (UTC)

Since this seems to be a thread of original research, I'll say mine as well. I'm of the opinion that we actually do remember every single dream (and indeed almost everything we experience in real life too), but 99% of the time we just can't access it because the brain stores these memories without any links to anything else to trigger the memory. My "proof" is that several times I've suddenly remembered vividly dreams which I had years ago, which I didn't even properly remember at the time I had them. 82.43.89.71 (talk) 13:01, 2 May 2010 (UTC)

I have some questions about your hypothesis:

1. Why would we evolve to store all of that useless information?
2. Why would we evolve to generate it all?
3. What is the point in storing a memory of a dream that we can't subsequently recall?
4. How do you know that you just "remembered" a dream you had years ago - and that your brain didn't just pop a random thought into your head at the instant you "remembered" it rather than at the time you think you remember it from?

You have no means to prove that you had the dream years ago...unless you wrote it down or something - and then you're remembering the thing you wrote - not necessarily the dream itself. Recovered memory is the term for a memory of something that you thought you'd forgotten. As our article points out: "the authenticity of recovered memories has often been challenged; in some cases recovered memories are fictitious". No matter how vividly the memory is suddenly recalled, it can still be completely false. So your "proof" doesn't stand up to careful scrutiny - and unless you can use your hypothesis to explain other things (like why it is that we remember dreams only when we wake up during REM sleep - and what the purpose of all of this complex mechanism is) - then it's not much of a hypothesis. SteveBaker (talk) 15:18, 2 May 2010 (UTC)

Evolution doesn't require everything to be beneficial, as long as it isn't significantly harmful. --Tango (talk) 22:36, 2 May 2010 (UTC)

But if it's not benefecial or harmful then it's just random so how could it become so widespread? Also, storing every single dream (and almost everything else) is harmful to the extent that you would need energy to store that information. Zain Ebrahim (talk) 23:42, 2 May 2010 (UTC)

Football

When a football is tossed into the air, it's usually spinning pretty fast. As the ball travels along its path, the axis of rotation changes and dips with the football. I was wondering what force causes the torque necessary to produce the change in angular momentum. 173.179.59.66 (talk) 20:29, 1 May 2010 (UTC)

Assuming you mean an American football, the answer is that gravity does that. The dynamics of a ball's flight is described by the science of ballistics, sadly our articles on ballistics are weighted towards the forensic aspects of firearms and handguns and bullet trajectories, but strictly speaking ballistics studies the motion of any non-powered flight. The article External ballistics discusses some of the forces at play, in some serious detail, and if you replace any mention of the word "bullet" with "football" you get the basics. Specifically, a football's flight is stabilized by the Magnus effect, which is also discussed at External_ballistics#Magnus_effect. To put it simply, there is a downward force on the football because of the interaction between the spinning ball and the air blowing past it as it sails through the air; this downward force tends to act more on the nose than on the tail. A ball thrown without spin will maintain the same angle in the air; such a ball, if thrown straight and with no other forces acting on it, will tend to land at the same angle thrown (thus, if thrown nose-up, they land nose-up). Spinning balls will tend to land nose down if thrown nose up. --Jayron32 20:43, 1 May 2010 (UTC)

Thanks. 173.179.59.66 (talk) 02:56, 2 May 2010 (UTC)

Coiling microphone cable during use.

Hi, when recording audio using a (battery) powered electret microphone, should I be concerned with the arrangement of the excess cable? Can it be coiled or will this lead to distortion of the audio recording? --84.13.77.150 (talk) 22:43, 1 May 2010 (UTC)

Try it and see. If it leads to distortion that you can't hear, does it really matter? --Tango (talk) 00:58, 2 May 2010 (UTC)

Of greater concern is avoiding laying the microphone cable next to an electric cord carrying AC power. If a mic cable is layed next to a power cord, you can get a mains hum in the mic circuit; if they must cross, always do so at right angles to minimize the effect. However, I am not sure that the mic cable poses too much of a threat to itself. --Jayron32 02:06, 2 May 2010 (UTC)

Jayron beat me to some points, but 84.13 are you thinking of the general practice in the Professional Audio industry to not coil cables? This is very likely to be more applicable to AC mains power cables, where if you do neatly coil up cable, you are effectively forming an inductor.(also see Inductance) Which means that any time the current changes direction, (which is 50/60 times a second) there will be a loss of power as heat. If you have a big pile of cables supplying a bank of power amplifiers at a rock concert, all neatly coiled, there is a risk of overheating, melting, shorts and fire. Though any cable that carries a lot of power where the signal changes continuously ie. audio speaker cables from the power amplifiers to a bank of 'high power' speakers will also experience the heating effect, to a lesser extent. See this website/section, Do not keep your cables coiled about 2/3 of the way down the page. This effect is unlikely to be noticeable with the cable of a battery powered microphone.
The 'inductors' action may also have an effect on the audio, but is unlikely to be noticeable, though as Tango says "Try it and see". And lay cables as per Jayron32 to minimise hum. If you coil your cables you are also more likely to get cross-talk between channels. --220.101.28.25 (talk) 02:52, 2 May 2010 (UTC)

Another source: John Vasey,"Concert sound and lighting systems " 3rd edition, page 10, 1999, Focal Press, ISBN 0-240-80364-7. --220.101.28.25 (talk) 03:49, 2 May 2010 (UTC)

May 2

Moth Help

I live in Boston, MA---my apartment is flooded with these tiny little moth type creatures.

They're incredibly easy to kill, but their numbers are becoming worrisome!

Is there a common moth that infests in this time of year, or mayhap a well known reason to be surrounded by them? We don't leave out food!209.6.54.248 (talk) 00:40, 2 May 2010 (UTC)

You may want to check your pantry, if you have one. If they are flour moths, you don't have to leave food out to have a problem. Looie496 (talk) 01:35, 2 May 2010 (UTC)

(edit conflict) Are you sure they are moths? I haven't known moths to swarm like that. Having grown up outside of Boston, swarming insects include mosquitos, gnats, and mayflys. The only one of those that may be confused for tiny moths may be mayflys. Do you live near a swampy area or wetlands like the Back Bay Fens or something like that? --Jayron32 01:40, 2 May 2010 (UTC)

Moths don't usually accumulate for food. Light is the more usual source. At university accomodation we have lots of them about where light is abundant. Regards, --—Cyclonenim | Chat  02:54, 2 May 2010 (UTC)

Make sure they aren't eating your clothes. If so, wash any clothes they've started on, with bleach. Then store them in an air-proof container (those Space Bags are a good choice). I had a problem with moths and found tiny brown worms (their larval stage) at the top my walls, adjacent to the ceiling. I went around the whole house and killed any that I found there, and they went away. StuRat (talk) 10:55, 2 May 2010 (UTC)

When I lived in an apartment, pest control was the landlord's responsibility. You might want to talk to your building superintendent or whatever that job is called these days. --Anonymous, 20:23 UTC, May 2, 2010.

Re-engineering the universe for increasing computational capacity

In "Computational capacity of the universe" (Phys Rev Lett 88 (23):237901), Seth Lloyd estimates the storage and cumulative data-processing capacity of the universe to be proportional to ρc⁵t⁴/ħ, where t is the age of the universe, ρ is its density, c is the speed of light and ħ is the reduced Planck constant.

From Moore's law#Other formulations and similar laws, I gather that human needs for data processing and storage are increasing exponentially, which means that eventually they'll outpace the polynomial growth that Lloyd's formula implies. This means that if our needs for computation are to be satisfied, the universe will eventually have to be re-engineered to accommodate them; and if that's to be done in a way that keeps the equation valid, either ρ or c has to start growing exponentially, or else ħ has to start decaying exponentially. (NB: I'm extrapolating to its logical conclusion the general observation that when reality and human needs come into conflict, it's reality that gets changed, at increasingly fundamental levels.) Has it been studied which constant would be best to manipulate, assuming equally straightforward ways are someday found to manipulate all of them? (I'd tend to favour c, given that it would have the side effects of lowering communication latency and extending the raange of interstellar travel, but I'm probably not aware of all the considerations.) NeonMerlin 03:35, 2 May 2010 (UTC)

You're not going to manipulate any of these constants; first of all there is no need given the size of the numbers involved. Humans are in no danger of exceeding the computational capacity of the universe, however defined, for any timescale measured in units smaller than billions of years. Secondly, your statement "when reality and human needs come into conflict, it's reality that gets changed, at increasingly fundamental levels" is patently rediculous. Fundemental physical constants, like the speed of light or planck's constant, can't be manipulated to magically "create" new computational capacity. Its just silliness. --Jayron32 03:51, 2 May 2010 (UTC)

I think he's trying to say that as scientists run out of technology to explain the universe they will almost be forced to make up elaborate stories to perpetuate their point of no return theories that constantly alter previous realities to compensate for the lack of human knowledge. —Preceding unsigned comment added by 98.221.254.154 (talk) 04:19, 2 May 2010 (UTC)

C is in that equation because of it's connection to energy. The amount of calculation a particle can do is related to it's energy, and the energy of a particle is related to c. The implication of this is that to change c you are also changing the energy content of every particle in the entire universe - and where would you get such energy? Ariel. (talk) 04:19, 2 May 2010 (UTC)

I don't buy this anyway - forget about the underlying technology and think only about speed-of-light issues.

What use is computational power if it's situated in the next solar system? A computer has to shuffle data around - and if it takes 4 years to ask for a number from Alpha Centauri and four more years to get the answer back, that's going to be a pretty spectacularly slow machine. In any computation, there is a trade-off between storing something for later use - and recalculating it when needed. As the size of the machine grows, the balance tilts towards recalculating rather than storing. So as your computer grows to the size of a planet (which, in effect, is what the Internet has become), you get a 'law of diminishing returns' where you have to cache information locally rather than reaching out across the network to get it. The bigger computer can store much more information - but it becomes so slow to fetch it that you have to store it locally.

When you think about a computer that's distributed between (say) here and Neptune - the round-trip time to ask for and get back some information is around 8 hours. So the result of any calculation that takes less than 8 hours is better computed locally than being distributed over the larger computer. We might want to use the storage system on neptune (for example) for storing all of the DNA sequences of long-dead people - on the grounds that we seldom need that within 8 hours of asking for it...but if Wikipedia were stored 8 hours away - it would be useless to us.

Now consider storage on Alpha Centauri. At 8 years access time, we can't even store the results of major research programs over there. If we stored the DNA sequence of some obscure plant over on that part of the system - then it would be simpler to re-sequence the DNA of the plant than it would be to fetch it from way over there. If we stored the design for an airplane over on Alpha Centauri, it would be faster to redesign it from scratch than it would be to fetch the old design from storage in memory outside of our solar system!

When you get to the scale of a galaxy - the round-trip time exceeds the duration of an entire civilisation. It's hard to envisage a question that a human might ask where the answer could still be useful to us when it gets here 100,000 years later. There would be no point in storing things in memory on the other side of the galaxy since there would be no way for any future member of your civilisation to get it back again!

When you get to the size of the universe, you have many more problems. You ask the question of a far distant galaxy - and by the time the answer gets back, we've evolved into a different species - or the sun has exploded and we've all moved someplace else. What possible storage or computational needs could we possibly have where the answer could be useful so much later? Why store something that your species could never possibly retrieve again in the future?

While we might want something with more power than we can reasonably fit into a few planets - we simply can't have that. Our present exponential growth of computing needs will ultimately be cut short. However, the amount of growth we have left with nanotech computers, quantum computers and biological computers leaves us an immense amount of headroom before we really start to hit these limits. Humans run into these kinds of resource limitations all the time...and ultimately, we cannot grow forever.

SteveBaker (talk) 14:01, 2 May 2010 (UTC)

I guess you make another point in favour of raising c, as soon as a way is found to do it. NeonMerlin 15:52, 2 May 2010 (UTC)

You can't just arbitrarily alter the value of c. By what means would you go about changing the way the Universe works? What part of the word "constant" escapes your understanding! --Jayron32 00:48, 3 May 2010 (UTC)

Indeed. E=m.c². So if you change 'c' you've either got to find enough energy from somewhere to keep the mass of the universe the same - or if you're stuck with a finite amount of energy - then the mass of everything in the universe would decrease as the square of the change in 'c'. So if, for example, you decided to increase 'c' so that you could get to Alpha Centauri in a few months, you'd need to increase 'c' by (let's say) a factor of 10. That would decrease the mass of everything in the universe by a factor of 100 - which would instantly cause all of the stars to explode because they wouldn't have enough gravity to withstand the radiation pressure. You can't just tinker with fundamental constants without causing major upsets. Changing 'c' is premium-quality craziness! SteveBaker (talk) 13:46, 3 May 2010 (UTC)

NeonMerlin, you should ignore Seth Lloyd; he's silly. And when you see growth that looks exponential, you should fit a logistic curve to it, not an exponential curve. -- BenRG (talk) 17:39, 2 May 2010 (UTC)

Aztec knives

What are these Aztec knives made of? Flint? --The High Fin Sperm Whale 04:58, 2 May 2010 (UTC)

The image description says that they're made of flint. Is there some reason you don't believe this? Dismas|^(talk) 05:07, 2 May 2010 (UTC)

This site [5] has one made of chalcedony from the Ethnologisches Museum (berlin). The light coloured ones in the picture in question (rhs) to me look like quartz, but it may simply be the light shining off them. --220.101.28.25 (talk) 05:26, 2 May 2010 (UTC)

Sorry, I missed the image description. However, there is such thing as lightly-coloured flint (see this). --The High Fin Sperm Whale 20:14, 2 May 2010 (UTC)

Quartz is very difficult to knap due to its prominent grains. Quartzite is sometimes used, but even that makes for a very rough finished product. When I first saw the question, I assumed they were going to be obsidian, which the Aztecs put to good use in making weapons, but these are indeed flint or chert. Matt Deres (talk) 23:35, 2 May 2010 (UTC)

Another spider question

How many spiders does one eat while sleeping during the course of one's life? Alaphent (talk) 09:41, 2 May 2010 (UTC)

A quick Google search suggests as little as 4 but as many as 7-8. Although this page suggests the whole thing is a load of rubbish. Dismas|^(talk) 09:54, 2 May 2010 (UTC)

"For a sleeping person to swallow even one live spider would involve so many highly unlikely circumstances that for practical purposes we can rule out the possibility. No such case is on formal record anywhere in scientific or medical literature," says a spider expert at the Burke Museum: http://www.washington.edu/burkemuseum/spidermyth/myths/whileyousleep.html Rimush (talk) 10:31, 2 May 2010 (UTC)

One such case is in a Post mortem report (video): Misadventurous ingestion of Musca domestica by geriatric female was initially treated by a chelicerate arthropod taken orally, with consequent evolution of treatments until equine injestion and consequent termination. Cuddlyable3 (talk) 15:21, 2 May 2010 (UTC)

I woke up once when a spider lowered itself onto my cheek, which was a close call. StuRat (talk) 10:45, 2 May 2010 (UTC)

The Straight Dope : Does the average person consume four spiders per year in his sleep?. This article discusses it a bit. In it, he explains why the chances of swallowing a spider during your sleep is virtually zero, except in the case where an egg-sac hatches nearby. In that case you might inhale a few new-born spiders. But new-born spiders are so tiny that you wouldn't even notice if you were awake. APL (talk) 16:12, 3 May 2010 (UTC)

Stupid insects and spiders

I've had numerous times when an insect or spider walked right up to me, or even on me, and then I promptly killed it. Can't they see me ? Don't they have an instinct to avoid animals a million times their size ? StuRat (talk) 10:45, 2 May 2010 (UTC)

We're so massively beyond their scale and world-view that I doubt that they (the ones that don't seem to react to our movements, that is - it may be different for the ones that feed upon us) even see us as lifeforms, nor possess the intelligence to see us as such. --Kurt Shaped Box (talk) 12:26, 2 May 2010 (UTC)

Isn't there a story in the Odyssey or Sinbad the Sailor of a ship's crew landing on the back of a floating turtle and thinking it's an island? If a human sailor, albeit mythical, with some 100 billion neurons in his brain, can conceivably make this mistake with a turtle a few hundred times his size, I can't see a spider, with a brain of a mere 100 thousand, could make such a distinction when walking on a human a few hundred thousand times its size. Tonywalton ^Talk 00:07, 3 May 2010 (UTC)

StuRat, what is your opinion of this? Count Iblis (talk) 14:28, 2 May 2010 (UTC)

(Baker's law of website design: Large fonts, too many colors strange placement of text on page == Nut-job - you don't actually have to read the text to know this with 95% certainty) SteveBaker (talk) 14:41, 2 May 2010 (UTC)

And actually, this is no place to discuss people's opinions of such things. This is a Reference Desk. --Mr.98 (talk) 20:01, 2 May 2010 (UTC)

I think being concerned with the lives or deaths of insects and spiders is silliness, except when they are helpful to us. I also find myself saving the lives of pretty insects, like butterflies and ladybugs (ladybirds), but most creepy crawlies can join each other in the tread pattern on my shoes. I was upset to find that a magnificent praying mantis, living at the entrance to my work, was killed. StuRat (talk) 18:20, 4 May 2010 (UTC)

A spiders' brain is a very tiny thing indeed. They don't have a lot of space to store all of the kinds of behaviors that might turn out to be useful. The have to prioritize. Web building - yep, that's necessary. Mating behavior - yep. Feeding - yep. Avoiding being eaten by a bird - maybe. But the probability of an individual spider being killed by a large animal is so amazingly small that the evolutionary benefit to carrying that around doesn't make it worth-while to do so. Spiders who somehow gained that ability would have to expend more energy to support the growth & maintenance of that larger brain - and (evidently) that extra 'cost' would exceed the statistical benefit. It's worth remembering that the spider couldn't "learn" this human-avoidance behavior - because the first failure means death. It also can't be taught the behavior from it's parent because spiders lack language and they don't hang out with their parents for very long. So this would have to be an 'instinctive' behavior...and that means that it has to be contained in the spider's DNA. So we're not only talking the cost of having a brain big enough - but also the cost for every cell in the spider's body of storing the "instinct".

Worse still, how many large animals actually go out of their way to kill spiders? Cows don't, sheep don't. I bet most large animals don't. That means that many species of spider didn't evolve with large spider-killing animals around them. Humans spread across the planet very rapidly in evolutionary terms - and many species are still playing catch-up. Even large, smart animals haven't evolved the necessary fear of humans. A large bear that might attack a human hasn't evolved to realise that we carry guns - or that if you do kill one of us, a posse of humans will come along the next day and hunt you down - or that if bears in general pose a problem for humans in general, we're going to round you all up and relocate you somewhere you don't want to be. Bears aren't stupid - they simply haven't had time to evolve to cope with the rapid pace of change on the planet.

A bigger question is why are you (an otherwise intelligent human) indiscriminantly killing spiders? All but a few species are harmless to us - and help keep the population of other insects (like flies and wasps) to a minimum. Flies and wasps are harmful to humans (flies spread diseases and wasps sting us). So we should perhaps ask instead: "How come large, super-smart animals like StuRat don't have an instinct to carefully avoid killing beneficial spiders?"

SteveBaker (talk) 14:39, 2 May 2010 (UTC)

That would be because, even if there's only a small risk of a spider bite, this risk isn't worth the even smaller benefit. Also, waking up with a spider crawling on you is just as unpleasant as an insect. StuRat (talk) 14:56, 2 May 2010 (UTC)

However here in the UK there are no harmful spiders at all, yet people still squash them, Perhaps people just don't like spiders. Tonywalton ^Talk 00:07, 3 May 2010 (UTC)

Some sources state that the factoid about eating spiders in your sleep is a myth, but while awake people eat more spiders and insects in food (example). As for killing spiders, there's a Russian superstition that killing 40 spiders brings a person good luck, and on the other hand some people eat fried spiders. ~AH1^(TCU) 23:47, 2 May 2010 (UTC)

@ StuRat so you don't ever do things with a small risk like driving, or crossing the road? These activities are way more risky than an encounter with a wee spider in the UK. Why not just say they frighten you because you've never taken the time to understand them. There must be a law somewhere that states that fear is directly proportional to the individual's ignorance of the feared object. Caesar's Daddy (talk) 07:57, 3 May 2010 (UTC)

I suppose you could call it ignorance, in that not knowing which spiders are harmful, we tend to just kill them all to be safe. As for driving, there's a huge benefit to driving, like allowing me to hold a job, while there's no such huge benefit to tolerating spiders on me. StuRat (talk) 13:48, 3 May 2010 (UTC)

Well, there are no harmful spiders in the UK - so if that's where you live, you can stop killing them without any additional risk. There is some benefit to tolerating them - so on balance, that's the rational thing to do. The main problem for the spiders, however, is not the rational - it's the irrational. Of course, here in Texas...not so much. We have quite a few nasty little buggers who certainly need to be squished on sight if found in your home. I've had one hand swell to twice it's normal size following a spider bite...it's no fun! But still, it doesn't take buy 10 minutes to dig out a list of venomous spiders and learn to recognize them. Brown Recluse and Black Widows get squished without a fair trial - but even so, some - like the pink-kneed tarantulas are quite magnificent animals and get treated to a half mile car trip in nice cosy box to someplace I can safely release them. SteveBaker (talk) 20:04, 3 May 2010 (UTC)

Steve, don't you know I'm from Detroit, by now ? Was that injury from a spider you were trying to save ? StuRat (talk) 18:25, 4 May 2010 (UTC)

Then, of course there is Cochineal - which is an insect from which red food coloring is made. Take a look at all the foods containing "E120" - 70,000 crushed insects per pound of coloring. SteveBaker (talk) 13:41, 3 May 2010 (UTC)

Burning fat without burning muscle

Hi. I've been working hard in the gym over the last few months, and I have developed quite big arms and chest muscles. Now, I would like to burn some fat which has accumulated in my belly in order to start developing a six-pack. Which kind of exercise is best to burn fat, without burning any of my hard-earned muscles? Is aerobic or anaerobic exercise better? Should I eat before the exercise, or not (so that the body burns fat faster)?

Thanks a lot! --81.44.96.96 (talk) 09:45, 2 May 2010 (UTC)

Keep excercising but eat less calories. 89.242.97.110 (talk) 11:11, 2 May 2010 (UTC)

Fewer calories is one thing, but the source of those calories is also important. For example, you wouldn't want to cut protein, as that's needed to maintain those muscles. StuRat (talk) 12:20, 2 May 2010 (UTC)

Western eat far more protein than they need anyway. 89.242.97.110 (talk) 12:26, 2 May 2010 (UTC)

On average, yes, but we still get many people on crazy diets who don't get enough. StuRat (talk) 13:09, 2 May 2010 (UTC)

The reverse is more likely. Excessive protein is bad for you, see Protein (nutrient) 89.242.97.110 (talk) 20:44, 2 May 2010 (UTC)

(ec) No, that ("Keep excercising but eat less calories") is not the answer. The answer is, be absolutely certain to eat 0.7-0.8 grams of protein per pound that you weigh to keep your muscle. For example, if you weigh 180 pounds, then 180 * 0.8 = 144 grams of protein. That's a lot! It's equivalent to the protein from 28 egg whites per day (ie two and a half cartons of eggs). Or a steak like this. If you eat less than that while continuing to exercise, you will lose muscle, period. (Of course, the easiest way to get your protein intake may be a protein powder). Now as for losing FAT while you exercise and retain MUSCLE, yes, it is true that if you eat fewer calories you will lose weight, but that is not the right way to lose weight while keeping muscle, as your body will realize you're only getting, say, 900 calories, and you will just lose fat and muscle and everything. The correct thing to do is to keep a normal intake, say 2500 calories, including, crucially the amount of protein that I listed (150 grams, say, if you weigh 180 pounds), absolutely continue to do weight training (if you don't use your muscles, they will disappear), do this weight training, say, every 3-4 days. Then, every day, get on the elliptical machine, and use it until it shows that you have expended 3500 calories. The elliptical machine, on a fair resistance setting, is a monster at burning calories. Now, you might not FEEL like you've just burned more calories than your whole daily intake (2500) but you did: the machine does not lie, as calories are a measure of physical work (ie a physics concept) and if you've done that physical work (moved resistance) by definition you have burned those calories.

So, that is where the fat-burning comes in. Now you must keep very strictly to a 2500 calorie diet, and every day burn 3500 on the elliptical machine on a fair resistance level. At that rate, you will lose 1000 calories per day. 1 pound of fat is 3500 calories, so every three and a half days you will lose a pound of pure fat. If you continue doing this, while not stopping with either the weight training, the proper amount of protein, and the 2500 calories of real good food, you can have a real six-pack, totally toned and defined everything, etc. I have personally developed a six-pack using the above methodology and can attest to it. Hope this helps. 84.153.248.35 (talk) 12:31, 2 May 2010 (UTC)

Even for a body-builder, I don't think your protein requirements would be as high as that. Exessive protein is just used as calories. Do you have any quality independant scientific sources for the above please? I imagine the sellers of high-protein supplements are going to try to convince you that you need a lot of it. 89.242.97.110 (talk) 13:03, 2 May 2010 (UTC)

Please refer to this [6] Science Desk question regarding protein intake and "strength training", from ≈4 days ago. It has references that look "quality independant scientific". (I must admit that I answered this question!). 89.242.97.110 is quite right to ask for references, they should always be provided. Ref.Weight_lifting_and_training
♥ Recommended 'normal protein' RDA (Recommended Dietary Allowance) is 0.8 grams per kilogram of lean bodyweight (1 kilogram=2.2 pounds) ie. Higher than what you thought was a high figure! exactly the same as I provided - see below.
♥ For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended.
Aerobic exercise would be best for 'fat burning' as it can be carried on far longer than anaerobic exercise. Short, high intensity exercise is not as good at calorie burning as moderate 'long term' exercise. See also Weight Loss/Dieting--220.101.28.25 (talk) 13:38, 2 May 2010 (UTC)

Particularly see the "Fat loss versus muscle loss" Section--220.101.28.25 (talk) 13:46, 2 May 2010 (UTC)

hey, we're saying the exact same thing! You just said "For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended" and your figure of 1.6 grams per kilogram is exactly the same 0.72 grams per pound that I listed!! So my number is the same as your number, 1.6 (in per kg). Now, your range goes higher, it goes up to 2.2. grams per kilogram you weigh. That is 0.99g per pound that you weigh. Even while you are trying to really body-build and gain muscle mass, I think that is just a teeny bit too much. You won't have any use of the extra amount over 0.8 grams per pound you weigh. But the low end of your range is 0.72, just like I said (0.7-0.8), and the high end of your range, 0.99, is just a little bit over what I said. So basically we are in total agreement. The original poster can go ahead and "play it safe" and take 0.99g per pound he weighs daily, or he can follow my advice and take 0.7g-0.8g per pound that he weighs. But we both agree that any more than that and he will not benefit, and any more than that and he will lose protein. 84.153.248.35 (talk) 14:23, 2 May 2010 (UTC)

Burning 3500 kcal on the elliptical each day is absolutely insane. That would take about 5.5 hours at normal resistance. And advising our OP to sustain a deficit of 1000 kcal a day without first talking to a doctor is NOT appropriate. This is why we have the no-professional-advice rule. Btw, the RDA for protein is (as 220 says) 0.8g per kg of lean body mass. Also, a lot of the energy your body burns is through normal metabolism - see Basal metabolic rate. Zain Ebrahim (talk) 14:59, 2 May 2010 (UTC)

To the OP: to get a handle on what 84 is talking about I recommend you read Basal metabolic rate and the article on Harris-Benedict equation might also be interesting. As for your question, I suggest talking to the personal trainers at your gym. Zain Ebrahim (talk) 15:06, 2 May 2010 (UTC)

← ← @84 No real need to whisper! ;-) I think here I have seen 0.8 gm and read it as per Kg not per pound. Perhaps not a good idea to mix 'imperial' and 'Metric' quantities ie 0.8 grams per pound is not as 'scientific' as we should try to be. I was actually answering 89.242.97.110s' comment that they thought the protein requirement was too high. So yes we are basically in agreement, with the references!. Throw a few conversions in here, 800 grams (1.8 lb), 1,600 to 2,200 grams (3.5 to 4.9 lb), the upper figure does seem high! But, everyones metabolism is different. Arnie Schwarzenegger could probably, once, have done that easily. And if it's not 'used' it will just be er, 'excreted'. Wasteful.

I was mainly trying to provide references, very important here. Doesn't matter what you know/believe to be true, must be wp:verifiable! Has been some real turmoil caused by editors, in all Good Faith, giving rather wp:POV opinions.

As Zain says (beating me to it) talk to a 'pro', though I'd suggest a nutritionist/ dietician or similar. We can't give specific advice for a person, we can't even see them! Guten Nacht! 84 and all. :-) --220.101.28.25 (talk) 15:53, 2 May 2010 (UTC)

Protein (nutrient) suggests 0.8g per kg for a mature adult, and the relevant reference from there also says that extreme amounts of protein is harmful. 0.8g per kg for a person weighing 180lbs is about 65g of protein. 100g of raw peanuts contains nearly this amount according to High protein diet, but many foods in the everyday diet already contain some protein so there may be no point in deliberately eating protein-rich food as the excess is just used as calories by the body. 89.242.97.110 (talk) 20:49, 2 May 2010 (UTC)

@81.44.96.96: This Men's Health article (entitled "how to lose muscle") has some very sensible suggestions. It amounts to eat, sleep, rest, and exercise sensibly; to break any of these you'd have to be behaving fairly immoderately . Unfortunately every gym has a few people who think progress is made only by suffering. -- Finlay McWalter • Talk 17:22, 2 May 2010 (UTC)

Good advice there, Finlay McWalter. Moderation in all things. This seems a good reference for Protein intake:"Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes", Journal of the International Society of Sports Nutrition. 2006; 3(1): 7–27. Published online 2006 June 5. doi: 10.1186/1550-2783-3-1-7. Retrieved 3 May 2010. --220.101.28.25 (talk) 15:05, 3 May 2010 (UTC)

Take your finger out of my butt, please...

With MRI and other technologies, are we getting any closer to eliminating the highly invasive digital rectal exam and colonoscopy ? The MRI seems to carry far less risk, so that would be another advantage. What's the current limitation preventing replacement, a lack of resolution in the MRI images ? StuRat (talk) 12:25, 2 May 2010 (UTC)

If you know another way of removing prostate fluid for microcellular examination post it here! MRI doesn't resolve down to cellular level AFAIK. --TammyMoet (talk) 13:00, 2 May 2010 (UTC)

I can think of one more enjoyable way to produce prostate fluid... However, I don't believe "removal of prostate fluid" is a normal part of either of the procedures I listed as candidates for elimination. StuRat (talk) 13:12, 2 May 2010 (UTC)

DRE is obviously cheaper and easier than any kind of other technique—it takes five minutes and a greased finger, and the analysis happens "in real time" without any money spent on fancy machines or their operators. So I doubt that's going away anytime soon, even if it isn't the most fun medical procedure in the world (it's hardly the worst, though—I don't find it as bad as getting blood drawn, personally). Colonoscopy is a different thing altogether. I suspect the problem is that current MRI tech doesn't allow the fine-grained manipulation of the colon itself, or resolve in color, that makes a big difference. The colonoscopy can also remove polyps in realtime as well during the procedure, and the tissue can be analyzed in the lab later—that's handy. An MRI is going to maybe tell you there are things in there, but still require you to go in and get them. So that's not as useful. --Mr.98 (talk) 13:48, 2 May 2010 (UTC)

Is the OP's dislike of the colonoscopy procedure based on imagined or actually experienced discomforts? I tolerated the examination easily and found the experience interesting. I was able to watch my inside view on a TV screen and discuss what was going on with the nurses. I was surprised to see that the colon bore is more triangular than round, and of course am reassured that nothing untoward was discovered. The only significant discomfort came as flatulence on my way home after the colonoscopy. MRI is slow to give a result, needs a major expensive installation, and this video may persuade the OP that it has its own risks: "There are obvious potential hazards to people and equipment in the area (of the MRI)...The magnet environment under certain circumstances can be a dangerous place...Complacency can be fatal." Cuddlyable3 (talk) 14:54, 2 May 2010 (UTC)

The other thing about a colonoscopy is that you can remove tissue samples at the same time, thus removing the need for two procedures. I had an MRI scan last year, and the procedure itself wasn't unpleasant. However, the recovery took days: I was disoriented and dizzy immediately, I couldn't drive home, and I couldn't sleep properly. Comparing it with the gastroscopy I had a few years previously, of the two procedures I prefer the gastroscopy! --TammyMoet (talk) 15:36, 2 May 2010 (UTC)

TammyMoet your account is interesting because there seems to be no reliable information about persisting aftereffects of MRI. If yours was not a (rare) reaction to the contrast agent you may have been given, I would ask whether you suffer from claustrophobia. Cuddlyable3 (talk) 17:18, 2 May 2010 (UTC)

No it wasn't a reaction to gadolinum, and as I had some free time after the procedure I spent some of it on the internet looking for the cause of my reaction. It doesn't appear to be that rare, and I left my experiences on a particular website which was set up by a radiologist in the UK collecting such experiences. I don't suffer from claustrophobia. I have my own explanation as to what happened, which as it falls into an area called by some "pseudo-science" or "woo woo" doesn't belong here. --TammyMoet (talk) 18:25, 2 May 2010 (UTC)

This is NOT MEDICAL ADVICE but you might find this article by Harriet Hall over at SBM interesting. Vespine (talk) 22:39, 2 May 2010 (UTC)

According to a couple of web links I dug up on the spur of the moment, the cost of an MRI ranges from $400 to over $2500 depending on the details of the procedure. Enough said, I think. Looie496 (talk) 22:52, 2 May 2010 (UTC)

That makes it more expensive than DRE, but I don't know about colonoscopy. Googling around seems to indicate that colonoscopies range from $1K to much more depending on what is done (assuming uninsured, in the US). --Mr.98 (talk) 23:38, 2 May 2010 (UTC)

CT and MRI are being evaluated as alternatives to colonoscopy (see virtual colonoscopy). There several significant limitations, however. For one, they're newer technologies, so we don't have studies showing that they are good screening methods (do people undergoing CT colonography have a lower mortality rate after 20 years? 30 years?). Also, the resolution is not nearly as good as direct visualization. CT involves ionizing radiation. MRI is quite expensive and wouldn't really afford a cost savings over colonoscopy. One of the major drawbacks is that the patient still must drink the preparation the night before (and in my experience, the part about colonoscopies that patients usually dislike is taking the preparation, not the procedure itself), so the virtual colonoscopy isn't necessarily more comfortable than actual colonoscopy. And then, finally, imaging studies have no way to obtain samples (until we develop a Star Trek–style transporter), so if there is any abnormality seen, the next step is to to a full colonoscopy (and another round with the preparation). Since polyps are seen on a fair number of colonoscopies, this would mean that a number of people would have to undergo two preparations and twice the expense. Regarding the digital rectal examination, it's fast, cheap, and safe. It's going to be very difficult to develop a replacement procedure. — Knowledge Seeker দ 00:17, 3 May 2010 (UTC)

soy

it seems overnight every fast food place in America switched to soybean oil and soy flour ect. im allergic to soy. what am i supposed to do? —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:30, 2 May 2010 (UTC)

Cook yourself, or don't eat fried food, or eat at a restaurant where they use different ingredients. Or perhaps you can desensitize yourself. Graeme Bartlett (talk) 13:41, 2 May 2010 (UTC)

Might this constitute medical advice? Consult with a physician to determine what would happen if you eat soy from a fast-food restaurant. If the consequences are serious (and we aren't qualified or able to tell you), then you should not eat at fast food restaurants (or anywhere that you can't verify soy-free ingredient lists). Nimur (talk) 13:43, 2 May 2010 (UTC)

not just fast food places use soy every restaurant does including places like chilies tgf Fridays, moes ect. they also put it it hot pockets. —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:47, 2 May 2010 (UTC)

Yes, eating prepackaged foods will require reading the label carefully for soy/soya. Making foods from scratch, like cutting up potatoes and frying them yourself, using an oil you choose, is a lot safer. StuRat (talk) 15:03, 2 May 2010 (UTC)

They will have made a decision based on profit margins. What you can do is write to them and explain that this means you can no longer eat there, since they do not offer a safe option for you. You can alert friends and family to your inability to eat at these places, so social events are held elsewhere (maybe someone's house): any enthusiastic friends might be encouraged to write to these places and explain that they are no longer able to hold their social events there, since they do not offer a safe option for you. Essentially, you make it clear to the companies that this decision has lost them custom. They might still consider it a good decision (who knows how this affects their profits), but you are adding weight to the other side.

I do sympathise: I've lived most of my life with someone extremely allergic to peanuts, and this sort of thing can accumulate. Luckily, things have changed over the years so that companies consider it in their interests to warn for nuts and peanuts, and some companies work hard to offer safe options precisely because there is a market for them. But eating out is still difficult, and always subject to change.

And, I hope it doesn't need saying, but absolutely do not follow Graeme's advice to attempt desensitizing yourself: people have died doing that. Any attempt at exposing yourself to something you are allergic to should be carried out under medical supervision, as advised by a doctor, so that you can be treated and even resuscitated if needed. 86.178.225.111 (talk) 15:08, 2 May 2010 (UTC)

My daughter has a sensitivity to both soy protein and cow milk protein, so I can sympathize. Who knew that virtually all brands of hot dog weiners have milk in them? Not I, until I had to start reading the labels on frigging everything. We have an article on soy allergy which helpfully contains a list of additives that do or may contain soy. Hope that helps. Some fast food places list ingredients and nutritional information on their websites, but beware of corporations that just don't give a crap about your health and lie to you. Matt Deres (talk) 01:24, 3 May 2010 (UTC)

I thought that desensitization was a medical procedure rather than something to try on your own. From examples I have heard, it is not very successful. Graeme Bartlett (talk) 21:39, 3 May 2010 (UTC)

It is: Allergen immunotherapy. Buddy431 (talk) 00:16, 4 May 2010 (UTC)

Indeed, but that's not the same as "desensitize yourself". That is "talk to your doctor about the possibility of being desensitized, and hear them explain whether that is typically successful for people your age with your allergy, and consider whether the procedure (carried out under medical supervision) is a good idea in your case". It's the difference between the babysitter feeding a toddler a peanut butter sandwich because she'd heard that a little bit of peanuts helped, and a medical procedure carried out starting with minuscule amounts of allergen under controlled conditions. The person I know with peanut allergies had to abort a similar procedure under medical supervision, because they reacted too much to skin contact with peanuts: the medical staff didn't consider it safe to proceed. Forgive the jumping in, but people thinking it's a good idea to try desensitizing themselves instead of as a medical procedure is a really bad thing. 86.178.228.18 (talk) 22:23, 4 May 2010 (UTC)

Deepest part of ocean

Mariana Trench says that "[it] is the deepest known part of the world's oceans". I would like to know:

1. What are the odds that there is a deeper part? (I admit that this can be seen as inviting wild speculation, but perhaps it can be quantified based on the percentage of as yet unsurveyed area.)
2. I understand that the entire World Ocean has been measured from space using gravity-based algorithms, but would this be accurate enough to detect narrow trenches?
3. If not, would finding a deeper part be down to essentially luck or are there ongoing efforts to systematically measure the entire World Ocean? (I believe various navies were quite active in this respect in the 1960s but they probably have better things to do now.)

Thank you in advance. 83.81.60.233 (talk) 15:35, 2 May 2010 (UTC)

Trenches are formed by subduction zones, hence they are very special parts of the sea floor. Common sea floor is much shallower. Given that we know pretty well where all the subduction zones on this planet are and that there is great interest in studying them in detail, I would guess that it is pretty certain that the Mariana trench is the deepest part of the ocean without actually knowing what fraction of the general sea floor has been measured. --Wrongfilter (talk) 16:31, 2 May 2010 (UTC)

We have actually had quite accurate maps of the sea floor for fifty years, after the advent of Side-scan sonar. Widespread seafloor mapping was what led to our modern understanding of plate tectonics. It is highly unlikely that a large seafloor feature on scale with the Mariana Trench would have been missed by this point. --Jayron32 00:42, 3 May 2010 (UTC)

All the trenches are known, e.g. Oceanic trench#Major oceanic trenches. They are hundreds or thousands of kilometers long, and not easy to miss given even cursory surveys of the ocean floor. However, finding the specific deepest point in a given trench requires detailed mapping. I wouldn't be shocked if there happened to be a spot in one of them that was a little deeper than Challenger Deep (the deepest known part of Mariana), but the longer that record stands the less likely it becomes that we will find anything deeper. Dragons flight (talk) 05:19, 3 May 2010 (UTC)

More to the point, the size of such a place would have to be very small in order to evade our surveys - there comes a point where you'd have to be talking about a narrow crack or hole smaller than the precision with which we're surveying the ocean bottom.

If we found a five centimeter wide crack that went down deeper than Challenger Deep - would we count that? What about a one meter wide cave that wiggled down deeper - would that count? Assuming the answer to that is "No" then it's safe to say that Challenger Deep is the deepest spot of any reasonable size - and that we won't find anything that big and that deep in the future. Of course, these ocean trenches are extremely geologically active (that's why they are the way they are) - so it's quite possible that some future submarine earthquake could open up a deeper spot - or perhaps even fill the deepest bit with lava or an avalanche and thereby make some not-so-deep place become the new record holder. On balance though - I think it's pretty safe to say that Challenger Deep is truely the deepest spot within reasonable criteria. SteveBaker (talk) 13:35, 3 May 2010 (UTC)

Also, it's not clear whether it would be possible to have a tiny (e.g., 5 cm wide) crack that extended several kilometers in depth. Material properties of rock and sediments don't favor such an unstable structure. (If it existed, it would soon cave or deform and fill in). This is another reason why we don't expect such features except in large-scale subduction zones. Nimur (talk) 14:39, 3 May 2010 (UTC)

The important points have been touch on, but to add one thing, space gravity surveys can and do resolve trenches - they are still several tens of kilometers wide, much larger than the resolution of the free-air gravity maps. Awickert (talk) 17:14, 3 May 2010 (UTC)

5 cm? We don't even have maps of most of the Earth's dry surface that are that well resolved. The best available maps of most of the deep ocean are about 1-5 square km per pixel. As high priority targets, the trenches may be better mapped than that (though extreme depth also makes it harder to get good resolution). However, in general I think you are being overly optimistic about how well surveyed the oceans are. Could a canyon or fissure be hiding down there? Certainly. Are any deep enough to matter? Perhaps not. Dragons flight (talk) 18:45, 3 May 2010 (UTC)

The best worldwide maps are probably the digital elevation model from the Shuttle Radar Topography Mission, which has resolution of about 30 meters per pixel worldwide (although I don't believe it actually has any ocean coverage - I'll have to check). It is available for free. I have also worked with airborne LIDAR data for small regions (e.g., an entire county) which has 1-cm accuracy per pixel. At this scale of map detail, we have to design optimization algorithms to determine whether we're looking at laser returns from plant-leaves, stems, or ground, etc. You can imagine the difficulties and the data volumes involved! I am not aware of any LIDAR technology that works underwater; but you can create very high-resolution SONAR, seismic, or bathymetry imagery; such data tends to be proprietary and there is definitely not full coverage of the Earth's entire seafloor. Again, if you can resolve to 5 cm, you have to worry about 5-cm-sized interference - like sediments swishing around on the seafloor, plant and animal life, and so on. The bottom of Challenger Deep is probably fairly rocky, and the water is probably fairly still, which might help, but there could still be time-variations of the sea bed. Nimur (talk) 11:11, 4 May 2010 (UTC)

Incidentally, I also work with SRTM and LiDAR :-). Neither are usable for bathymetry because of attenuation in water. Global bathymetry is from free air gravity anomalies, and goes down to 1 arc minute (a little under 2 km). More precise bathymetry is given from ship tracks, and I imagine that this is used to ground-truth the free air gravity maps, but as others have said, this is not anywhere near global in extent. Awickert (talk) 02:03, 5 May 2010 (UTC)

Activating the Deepwater Horizon blowout preventer

Is there some intrinsic reason why this has been so difficult so far? Couldn't a blowout preventer be designed for wireless activation -- just press a button on a command ship and it stops flow? Or is there some fundamental reason that this is not an option when designing these things? Vranak (talk) 17:20, 2 May 2010 (UTC)

Wireless signals (radio) does not work under water. Radio waves are pretty much totally blocked by seawater. But take a look here - there are acoustically activated devices, since sound travels pretty well. Ariel. (talk) 18:39, 2 May 2010 (UTC)

Wireless signals do work under water, but not well. They are used to communicate with submarines: [7]. --Phil Holmes (talk) 10:26, 3 May 2010 (UTC)

My understanding of this event is that any such equipment on the rig itself would have been destroyed in the initial large explosion, subsequent fires, and the sinking of the rig's wreckage, and that no such intact and working equipment is still in place on the seabed, even if it was there in the first place, bearing in mind that at the time of the blowout the well was being modified rather than being in routine production. 87.81.230.195 (talk) 21:39, 2 May 2010 (UTC)

When the rig blew up, that did sever the communications with the preventer, but within the first 48 hours there were remotely operated subs at the site trying to trigger it. Apparently, the preventer isn't closing even when told to do so. Failure to activate, even when told to do so, indicates a more fundamental problem than just a communications issue. Dragons flight (talk) 22:11, 2 May 2010 (UTC)

I think that the valve itself may have been wrecked by the explosion. FWiW 67.170.215.166 (talk) 02:17, 4 May 2010 (UTC)

Thanks very much guys. Vranak (talk)

Bacon curling

Why does bacon curl up when you cook it on a grill? I presume it'd be due to drying out, so there's less hydrolysed protein and thus curling would occur (the opposite to when your hair gets straighter when you shower) but I'm not sure if that's the actual reason. Regards, --—Cyclonenim | Chat  20:39, 2 May 2010 (UTC)

I don't know chemically what's happening but I've cooked a LOT of bacon I have thought about it so I'll tell you what I've observed:) I believe it is not the "meat", not the fat and not the rind that causes the curling, I think it is the sinewy connective tissue between the fat and the meat. I think it shrinks when it cooks and this is what causes the curling. I bake my bacon now because I like it really crispy and it's much easier IMHO in the oven and curling doesn't matter so much. But when I used to fry it, there was 3 spots on the bacon, where the fat "meets the meat" that I would cut through to stop it from curling. Vespine (talk) 22:29, 2 May 2010 (UTC)

I am pretty sure the curling comes from differential heating of the bacon. As noted, bacon consists of at least 3 different tissues: fat, meat, and connective tissue. All three of these will cook at different rates, and as they cook will contract or expand at different rates. Also, when you fry bacon, you set up a LARGE temperature differential, as the part of the rasher in contact with the pan is a LOT hotter than the rest of the bacon. Since baking bacon tends to evenly distribute the heat over all parts of the rasher, there is less curling. They make a device called "bacon press" designed to counteract this curling; you see them alot at diners where they make a lot of bacon on a griddle. See this Google Image search which shows you the many different styles of bacon press. The ones I have seen most often look like heavy rectangular trowels, but they come round and pig shaped as well. --Jayron32 23:56, 2 May 2010 (UTC)

I agree with Jayron; it's the temperature difference. And forget using a "bacon press" - cook your bacon on a cookie sheet with a rack. Place the bacon in a cold oven, set the thermostat for 400F, and cook until done (time will depend on thickness). Yum! Matt Deres (talk) 01:30, 3 May 2010 (UTC)

I endorse the oven method, and I'll add that the oven temperature is not at all critical... anything from 325–425 F works (at least), so if you're baking something else, you can probably throw the bacon in and it will be fine. The cooking time will, of course, vary with temperature. I've read that higher temperatures result in more bitter-tasting compounds, so I tend to use the lower end of the range, but I'm not sure it actually makes much difference. -- Coneslayer (talk) 13:11, 3 May 2010 (UTC)

To be honest the actual curling has never caused me any bother :P I tend to just grill mine plain and simple -- comes out curled but very tasty. Thanks for all the interesting answers. Regards, --—Cyclonenim | Chat  14:49, 3 May 2010 (UTC)

Electron excitation - discrete?

In A level physics, we are taught that an electron can be excited to a higher energy level by means of absorbing a photon, on condition that its energy exactly matches the energy difference between the levels. This makes sense, there doesn't seem to be a mechanism for where the "excess" energy goes. However, this can't really be correct, surely? I mean, you could never get it exactly the same. And this sort of thing happens all the time in the real world (e.g. in fluorescent tubes' outer coating). What actually happens? (Unusually, excited state seems to be written for the layperson, and hence fails to approach the issue.) 92.23.14.145 (talk) 20:43, 2 May 2010 (UTC)

I'm by no means a trained physcist so I'll let others rip apart my answer in due course, but this seems to me like just a fallacy in human logic rather than questioning whether it's actually true or not. "...get it exactly the same" - There is no "getting", there are stupidly large numbers of photons (and electrons) around, the chance of some being of the same energy is, I imagine, pretty high. Also, because energy is distributed in packets (quanta), the possibilities are slightly limited as the energy values have to be a certain factor of some constant (someone remind me which?). Regards, --—Cyclonenim | Chat  00:20, 3 May 2010 (UTC)

Ok, so in A level physics you have learned that atoms have precisely defined energy levels and that transitions between these levels are possible by absorpion/emission of photons which in this picture would ahve to have exactly the energy difference between the energy levels. You have correctly noted that this picture cannot be exactly correct.

What is wrong with this picture is the idea that an atom can both have an infinitely precisely defined energy level and be in a state that changes as a function of time. The precisely defined energy levels only appear if you ignore the coupling of the atom to the electromagnetic field. If you take this approximation serious then the atom cannot make any transitions as no interaction with the electromagnetic field means that it will not interact with photons at all.

The moment you take into account the fact that atoms do in fact couple to the electromagnetic field, then what you see is that the "energy levels" are no longer states with a precisely defined energy. The spread in energy of a state is inversely proportional to the spontaneous decay time of that state. One can heuristically unbderstand this using the time-energy uncertainty relation.

In practice this means that atoms can absorb photons that are within the the energy spread. Now this energy spread is quite small, but then each atom will have some random velocity causing its energy levels to appear to shift due to the doppler effect. This causes a gas of atoms to be able to absorp photons of a larger range of energies. This is called doppler broadening. Count Iblis (talk) 01:29, 3 May 2010 (UTC)

It's also worth pointing out that it is quite possible for photons of exactly the right energy to exist. Where the electromagnetic radiation (typically light) is created by an incandescent source (i.e. one that uses heat to produce the light), then the light produced is a broadband of every wavelength within the band. So the atoms only absorb the light whose wavelength exactly matches their energy gap. Hence Spectral line. --Phil Holmes (talk) 09:39, 3 May 2010 (UTC)

Spectral broadening is the article that should help see Spectral_line#Spectral_line_broadening_and_shift - the lines in practice are non-zero width.Sf5xeplus (talk) 10:46, 4 May 2010 (UTC)

hot water

recently my hot water tastes and smells like scouring powder. my cold water is fine. can someone explain this? —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:57, 2 May 2010 (UTC)

It might help someone to answer if you give some details about how your particular hot water system works: mains-fed instant gas heater, electrically heated hot water cylinder, hot rocks in a leather cauldron? (OK, the last isn't very common these days.) 87.81.230.195 (talk) 21:26, 2 May 2010 (UTC)

its a hot water heater tank. heated by either gas or electricity. —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:12, 2 May 2010 (UTC)

The hot tap water in your tank may contain extra chemicals to treat the water. ~AH1^(TCU) 23:35, 2 May 2010 (UTC)

It may be water softeners? --Jayron32 23:43, 2 May 2010 (UTC)

That would be my guess, particularly if they just added a new batch of salt to the water softener or if it's been sitting for a while unused. Under those conditions you can get excess salt in your water. If the water softener is hooked up after the water heater, try bleeding some water directly off the hot water heater to see if it's good. If so, that would seem to implicate the water softener. It could just be a bad batch of salt in there, which isn't sufficient compacted, and thus dissolves too readily in the water. StuRat (talk) 01:53, 3 May 2010 (UTC)

"The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulfide." [8]. You can change the rod to aluminium (they just unscrew out, although it might be hard to do in an old tank), or add a carbon filter before the water. If you choose a filter make sure you get one designed for it - otherwise it will clog up very fast. Ariel. (talk) 02:18, 3 May 2010 (UTC)

Infrared rainbow

Yesterday I took a near-infrared picture of a double rainbow. As expected, the two arcs are displaced towards each other relative to a visible-light rainbow. Is there a frequency at which the two arcs merge, and if so, what is it? --Carnildo (talk) 21:21, 2 May 2010 (UTC)

This region is called Alexander's band, and is discussed in both that article, and in the article Rainbow. Presumably, there will be some point at which the wavelengths of light from the two bows are identical as they pass one another; however I see no reason why this overlap point would be identical for every rainbow; it may be unique for each observer. --Jayron32 23:42, 2 May 2010 (UTC)

I can't see any reason why the overlap point wouldn't be the identical for every rainbow. The critical angles for total internal reflection are determined by the properties of water and air, I believe, which are essentially constant (on Earth, at least - other planets, eg. Titan, have different angles). --Tango (talk) 01:28, 3 May 2010 (UTC)

The two rainbows may very well never meet since the refractive index of water is not a monotonic function of the light's wavelength. Dauto (talk) 04:48, 3 May 2010 (UTC)

May 3

Plutonium

In the Simpsons, Homer's bag has plutonium in it and the police dynamite it, causing a nuclear explosion. Would this happen in real life? --75.33.219.230 (talk) 00:13, 3 May 2010 (UTC)

It wouldn't cause a nuclear explosion, but it would disperse toxic plutonium into the air. Think dirty bomb, not nuke. A decent real-life analog would be the 1968 Thule Air Base B-52 crash. Messy and expensive to clean up. Few if any immediate deaths; maybe some long-term health problems if plutonium was inhaled. Bad, but not as bad as a full nuclear explosion. (Making plutonium detonate in a full nuclear explosion is not easy—see Fat_Man#Technology for a decent description of why.) --Mr.98 (talk) 00:45, 3 May 2010 (UTC)

To explode a nuclear bomb you need to have enough material in one piece to reach the critical mass for the element. That's more or less it. The trouble is that when you have anywhere near that amount it starts to get really really hot and radioactive. So what you go is make a number of small pieces, and when you need it to explode shove them all together into one piece (like imagine a pizza, pull all the slices apart, then when it's time to explode push them all back together into a circle). Just exploding the plutonium will not make a nuclear explosion - it will just send plutonium everywhere, which will do exactly the opposite, since now you have lots of small pieces instead of one big one. Ariel. (talk) 02:26, 3 May 2010 (UTC)

This is not, in fact, how plutonium bombs work (so far as we know), but is a common misconception. Plutonium weapons use a solid piece of plutonium that is then compressed to a a high density. If you split plutonium into multiple pieces and then tried to combine it, you would have a fizzle, because the combination speed would be slower than the reaction speed. Nuclear weapon design has more detail on implosion physics. It is not the "small pieces" model, though this is often how it is erroneously explained in textbooks or encyclopedias (but not Wikipedia). --Mr.98 (talk) 12:02, 3 May 2010 (UTC)

Ummm, actually that is how Gun-type fission weapon operates. Implosion types mentioned above are more powerful, and are most likely the design used by the developed nuclear powers. Googlemeister (talk) 14:10, 3 May 2010 (UTC)

The article you linked to says plutonium CANNOT be used for gun-type fission weapons. --99.237.234.104 (talk) 20:15, 3 May 2010 (UTC)

From my reading it was because of the Pu240 impurities that were not removed in 1940s technology plutonium enrichment (with results similar to Helium 3 contamination), not that it was an inherent property of plutonium itself. Perhaps even with today's production methods we still can not remove the 240, or it is not cost effective? Googlemeister (talk) 20:55, 3 May 2010 (UTC)

This is getting a bit tangential, but while we're all here... the reason you don't remove the Pu-240 is twofold:

1. It is not cost effective. If you can remove Pu-240, then you can also enrich uranium (both require the same level of technical development). So in that case, you have a product flow that looks like this: uranium metal -> reactor -> processing fission products -> enrichment. If you have the technology for enrichment, you can make it just uranium metal -> enrichment and skip the whole reactor phase. (To your credit, you don't have to enrich as much as you do with the uranium. Though it might be harder from a physics point of view... I don't know if the 1 neutron difference between Pu-239 and Pu-240 would change things a bit, as compared to the three neutrons between U-235 and U-238.) You can reduce the Pu-240 levels by varying the way you have your reactor make plutonium, but not to levels that it will work in a gun-type weapon without fizzling, I don't think.
2. More importantly, plutonium is nasty and messy. It is more volatile and toxic than uranium, especially in a gaseous form. I'd think the last thing you'd want to do with plutonium is to make it into a gas and then spray it inside your enrichment machines. The contamination level would be much higher than with uranium and require a lot more expense and effort.

To my knowledge no nation has tried to use plutonium in a gun-type weapon. When they did want gun-type weapons (say, for artillery shells), they used U-235. For everything else, implosion is a far more efficient use of material.

Separate from this is whether the "pizza" design (which is in fact how the plutonium implosion is sometimes depicted and was even considered as a possibility very early on in the project before implosion was invented) would work. It's basically a spherical gun-type design. I don't think any powers ever made weapons this way, probably because the amount of symmetry necessary is probably quite difficult to pull off. (Implosion is hard, too, but if you get it working correctly, it is almost certainly more efficient than any variation of the gun-type design.) Anyway, it is not how any plutonium bombs have ever worked, as far as anyone knows. True implosion is much more efficient. There are ways to do it that involve imploding spherical shells of plutonium (you can fill the center with DT gas for boosting), but again, this is real-deal implosion and not spherical gun-type. --Mr.98 (talk) 00:02, 4 May 2010 (UTC)

Voice

I was wondering, hypothetically, if is it possible to prevent a boy's voice from breaking at puberty. I saw something on TV that put this question in my mind. Of course, I mean without surgeries, medications, etc. Thank you. 76.230.212.190 (talk) 01:07, 3 May 2010 (UTC)

I think you have ruled out the two methods that would work. Castration works (see Castrato for a description of precisely that) and I would expect hormone treatments (well, some kind of hormone suppressant) to work too. I can't think of any other way to do it. --Tango (talk) 01:31, 3 May 2010 (UTC)

(e/c) You'll need one or the other, unless the boy just happens to naturally keep his boyish voice - rare, but not unheard of. See our article about castrati and Kallmann syndrome for a semi-natural way this sometimes occurs. Matt Deres (talk) 01:34, 3 May 2010 (UTC)

You're missing another possibility: Don't speak for the entire length of puberty. Then your voice wouldn't break "at puberty". Of course, it'll probably break constantly when you start speaking again due to atrophy from disuse, but you didn't ask us to solve that problem. —ShadowRanger ^(talk|stalk) 20:56, 3 May 2010 (UTC)

Joke aside, voices crack for a lot of reasons. Puberty makes it nearly inevitable that it will occur sometimes, but you can do things to reduce the frequency. Tensing up makes cracking more likely, so try to relax. Cold water can temporarily constrict the vocal chords, so don't speak for a few seconds after taking a sip of ice water (or drink lukewarm or room temp water). The longer you speak, the drier your throat will get, increasing cracking, so you should drink, just avoid the really cold stuff. You can find other examples online; these tips are generally useful to public speakers of all ages. —ShadowRanger ^(talk|stalk) 20:56, 3 May 2010 (UTC)

River Geometry

There are rivers with various depth and width of flow.How do these parameters get fixed in the nature.Which laws of nature governs them ?.Are there any mathematical relationships? —Preceding unsigned comment added by Amrahs (talk • contribs) 02:23, 3 May 2010 (UTC)

I would assume the depth is related to how hard the material on the land is - soft earth will wash away and make a deep river, while rock won't (at least at first, the longer the river runs, the deeper it gets). The width of the river is related to the topology (elevations) of the land. Gentle hills will make a wide river, steep ones will make a narrow ones. Next the amount of water in the river depends on whatever is feeding that river. Once you know the amount of water, and the size of the river you get the flow rate. See Meander for information on why rivers make those strange winding shapes, it's quite interesting. Ariel. (talk) 02:29, 3 May 2010 (UTC)

Oddly enough, Wikipedia has an article that covers much of this, in some detail. See River. WHAAOE! --Jayron32 03:47, 3 May 2010 (UTC)

There is some maths or 'laws' associated with the branching of rivers, but I do not recall where to find it. 92.28.253.63 (talk) 11:02, 3 May 2010 (UTC)

Rivers are also somewhat fractal in nature, meaning that the rivers are similar to the rivulets which feed them, which are in turn similar to the creeks which feed them, other than scale. StuRat (talk) 13:20, 3 May 2010 (UTC)

Some of the early fractal work was developed by some colonial English engineer whose name I forget, H.... I think, who collated and studied time series for the periodic flooding of the Nile. Edit: it was Harold Edwin Hurst. 92.28.253.63 (talk) 15:22, 3 May 2010 (UTC)

Most of the properties of a river depend on its sources, the distance it has to travel to get to the sea - and the nature of the terrain in between. The ultimate source of a river is rainfall or snow-melt on high ground someplace. Because the water has run downhill, it tends to gather together to make small streams - and those streams merge to make a river. Because the water can only flow downhill, it will fill in hollows in the land to make ponds and lakes - and generally run down the bottoms of valleys. The nature of erosion means that over geological time, the river will make it's own valleys by wearing away the soil and rock and carrying the resulting sandy stuff down-stream. Rivers also get twisty because if (for example) there is a large, hard rock on one side of the river bed - it'll deflect the water off to the side, towards the other bank. If that bank is softer, it'll get eroded - allowing the river to make a diversion around the rock. That diversion points the flow of the water towards another bit of ground - and that too erodes.

These processes are sufficiently complex - and so sensitively dependent on things like precisely where a particular (now completely eroded) rock was half a million years ago - that although we understand all of the processes very well, and can make pretty good mathematical models - we can't predict the precise shape or flow rate of any particular river from first principles.

SteveBaker (talk) 13:24, 3 May 2010 (UTC)

Isnt that all obvious? 92.28.253.63 (talk) 15:20, 3 May 2010 (UTC)

Although most of what Steve says is pretty much correct and very straightforward, I will disagree with him on two counts. I think that we can pretty well figure out what shape a river will have (braided, meandering, etc.) based on a combination of bank cohesion, sediment flux, and aggradation rate. And although what Steve says about being deflected around rock and boulders is probably correct in itself, it is not generalizable in that way. Meandering in itself is actually a self-forced phenomenon by which any irregularity in the channel will cause the flow to become nonuniform and focus high shear stresses in one location and lower ones in the others. This in turn focuses zones of erosion and deposition in a positive feedback that gives the meandering river patterns that we see. (Likewise, this gives the patterns of bars in braided streams.) Awickert (talk) 20:48, 3 May 2010 (UTC)

There's a useful introduction to fluvial geomorphology here [9]. DuncanHill (talk) 13:27, 3 May 2010 (UTC)

(outdent) I actually work as a sedimentologist / fluvial geomorphologist, so I might be able to help!

1. First, the river article is really bad in terms of geomorphology and doesn't mention hydrology much. Fixing it up has been on my mental to-do list for a while, but you know how those things go...
2. River channel morphology is controlled by events that are large enough to move sediment and/or erode the bed or banks. Most flows do not change the channel.
3. There are downstream relationships (empirically-derived) that give the depth, width, and slope of rivers as a function of discharge. See river regime. But this doesn't answer your question.
4. The width of a river channel with noncohesive/nonvegetated banks is given by a critical value of shear stress against the channel banks. If the river is narrow (relative to the difficulty of its flows to carry bed sediments), the shear stresses on the channel walls will be higher than a critical value to move these sediments. Therefore, the banks will erode. But as a channel widens, bank shear stresses decrease. If it overwidens, this will result in deposition on the banks. This is how a channel maintains its width as well as its width:depth ratio. There are a whole ton of theoretically-sound (i.e., not just empirical) equations that describe this, but the end product is what I wrote here.
   • This changes with the application of bank cohesion (e.g., vegetation), but the same principle applies. It is just much harder to erode the banks, so the flows are deeper and narrower.
5. An endmember of bank cohesion would be a bedrock channel, and results in a completely different morphology because bedrock channels are sediment-supply-starved. Here, the channel is able to incise a deep canyon (much deeper than its flow depth) because it erodes its bed, but doesn't have a sufficient sediment supply for much deposition to occur.

Hope this helps, Awickert (talk) 17:34, 3 May 2010 (UTC)

space-time continuum

Do anybody 'feel' the 4-dimensional space-time continuum in everyday life? —Preceding unsigned comment added by Amrahs (talk • contribs) 02:28, 3 May 2010 (UTC)

Space time? Then yes - everyone. 3 dimensions space, 1 of time. Do you mean 4 space dimensions? Then no. Ariel. (talk) 02:32, 3 May 2010 (UTC)

If you're talking about 4 spatial dimensions (plus time), then the question is a slightly tricky one. Obviously nobody directly perceives anything more than 3 spatial dimensions, but if string theory is correct and we actually have over a dozen dimensions - then in a sense, the mere existence of everything around us would be a consequence of all of those dimensions - and because we 'feel' all of those things, we are all feeling the consequences of those additional dimensions. String theory claims that these extra dimensions are "small" so we can't detect them. Think of this as being stuck inside a long, narrow tube - the length of the tube allows use to move freely along it - but it's so narrow that we can't move sideways or up and down. In this situation, we have one 'large' dimension, and two 'small' ones. Of course, in such a situation, we can see the sides of the tube and be aware of their proximity because even though those dimensions are small, they are still larger than our bodies. But the extra dimensions in string theory are very small indeed - much, MUCH smaller than the size of an atom. So small, that we don't even notice that they are there - and so small that we have been unable to devise a means to measure or even detect them. SteveBaker (talk) 13:13, 3 May 2010 (UTC)

Isopropanol, Peroxides can Result in Explosion & Injury?

i was reading the article on here and it says Isopropanol can form Peroxides? i keep my bottle with out the cap on. does that help? how can i test for peroxides? also if it forms them wouldent that make it caustic? i use it on my skin. —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:03, 3 May 2010 (UTC)

See Peroxide, especially the safety section. I am not sure isopropanol itself is much of a problem, but acetone can spontaneously form acetone peroxide and many ethers can form ether peroxides. It generally takes a pretty powerful oxidizer to oxidize an alcohol to a ketone, but from the ketone or ether to a peroxide, something as simple as excess oxygen and a radical initiator, like UV light, could do it. You could also run into serious trouble if you mix ANY organic compound with hydrogen peroxide, and many households have both hydrogen peroxide and several common organic compounds together. Not sure it's a huge problem in your bathroom cabinet, but it may be. --Jayron32 03:45, 3 May 2010 (UTC)

Here's the article, if anyone's interested: Isopropyl alcohol. The sources cited for the peroxide claim include a materials safety data sheet [10] and an incident report [11]. The MSDS claims that it "may react with oxygen in the air to form peroxides", while the incident report claims that "The probable cause of this explosion/injury was peroxide formation associated with Isopropanol, perhaps accelerated by grease metal/solvent reactions". It further elaborates that "Literature review indicates that Isopropanol, with air contact, can develop peroxides, which can explode when concentrated". However, the big thing to note in the incident is that the isopropyl alcohol was concentrated overnight, making a probably insignificant concentration of peroxides into an explosive concentration. Jayron's probably right that it's hard to oxidize isopropyl alcohol to acetone, so the concentration of peroxides built up in most cases will be extremely low. However, the moral of the story is:

1. Keep your isopropyl alcohol in a closed container, and don't open/close it frequently.
2. Don't concentrate any potential peroxides by allowing a large amount of isopropyl alcohol to evaporate.
3. If you are going to concentrate or heat the alcohol, test for peroxides first.

I don't think it's a big deal for households with isopropyl alcohol: if it was, we'd hear a lot more about it. This incident had a lot of factors that made an explosion possible (keeping it uncovered overnight, evaporating it to concentrate peroxides, and heating), none of which should be present at home. Furthermore, when reading the incident report, it appears that even the suppliers and lab workers were unaware of the danger, indicating that it doesn't happen very often, even under these more favorable conditions. Buddy431 (talk) 05:31, 3 May 2010 (UTC)

The peroxides are usually formed in small amounts - typically around the cap - the danger (in addition to the damage caused to a person by the exposion) is that when they explode they will break the bottle and/or ignite the rest of the liquid.

An additional precaution is to keep the bottle in a dark place (no light). Sf5xeplus (talk) 10:51, 4 May 2010 (UTC)

Before big bang

What was there before big bang ????????? --Extra999 (Contact ^me + _contribs) 10:50, 3 May 2010 (UTC)

A black hole according to an article "It's black holes all the way down" by Ben Gilliland in the Metro (Associated Metro Limited) of 30 April 2010, pages 22-23. It mentions an URL www.cosmonline.co.uk but I have not been able to find it yet. dit: You could see it here http://e-edition.metro.co.uk/home.html but it requires giving an email address (which is not verified). In the e-edition, its on pages 24-25. 92.28.253.63 (talk) 11:03, 3 May 2010 (UTC)

What was where before the Big Bang? --KägeTorä - (影虎) (TALK) 11:12, 3 May 2010 (UTC)

In fact, there may not even be a "before", as both time and space came into being at the big bang (but that's only one possibility, per A Brief History of Time). --Stephan Schulz (talk) 11:40, 3 May 2010 (UTC)

See also (seriously) Turtles all the way down, which does discuss the issue. --Jayron32 12:13, 3 May 2010 (UTC)

I usually respond with the question: "What was there bewhat the Big Bang?" :-) - DVdm (talk) 12:35, 3 May 2010 (UTC)

There are quite a few possibilities - and we don't know which is true, and (worse still) there are reasons to believe that we may not ever be able to know which is true. Certainly one possibility is that both time and space were created at the instant of the big bang - hence there is no "before" and no "there". Other possibilities are that the universe is cyclic with big bang leading to expansion, then slowing, then collapse and finally a big crunch that would be the source of the next big bang. Another possibility is that the universe is symmetrical in time - with the history of the universe being played out backwards before the big bang. Right now, most of this stuff is speculation. The best answer is "We don't know" - and I'd say that Occam's razor suggests that time and space both started at the big bang - so there simply was no "before". This is hard to get your head around - but there is no guarantee that physics will be readily comprehensible to human minds. SteveBaker (talk) 12:52, 3 May 2010 (UTC)

The other posibility is that the big bang represents a sort of "cosmic censorship" (see cosmic censorship hypothesis) in that, since it represents a singularity, that is everything is in the same place at the same time, there is no means of extrapolating anything earlier than the point of the big bang, meaning that while we may idly speculate as to what (or when) anything (or anytime) existed before the Big Bang, its moot because the nature of the big bang makes it impossible to verify any hypothesis about what may have existed before it. --Jayron32 12:56, 3 May 2010 (UTC)

A big mind-boggling question is why is there any universe(s) rather than just nothing. 92.28.253.63 (talk) 16:37, 3 May 2010 (UTC)

Depends on what you mean by why. If you mean "what processes brought the universe about instead of nothing happening at all" then see anthropic principle. At worse, its a meaningless question because we are here to ask the question in the first place, if the universe did not exist, there would not be an us to question why it did not exist. If you mean "for what purpose was the universe created instead of leaving behind nothingness" then you are starting to veer into territory that religion or philosophy rather than science is equipped to answer. Immediately below this post, SteveBaker will come saying that science is perfectly well equipped to answer questions of grand purpose, and then give no qualifying statement, or propose any experiment or method which would show how science could answer such questions. --Jayron32 18:25, 3 May 2010 (UTC)

That's a little unfair. I've already said that we may not ever be able to know the answer to this. The reaction that you are referring to happens when someone says that it's not science's business to be investigating these matters - or that this is a subject only for philosophy or religion or UFO researchers or some other bogus field. That's something I do take objection to. If there is a way to investigate something, science should absolutely do that - there are no areas that are "off limits". However, there most certainly are situations (and this may well be one of them) where it is not possible - even in principle - to know the answer. But the proof of that applies just as well to philosophers and religious types. Proof of impossibility is still proof. SteveBaker (talk) 21:22, 3 May 2010 (UTC)

Sorry about mischaracterizing your standard arguement. I fully agree that there are no areas of which science should be "off-limits". Still, there is some stuff which science is clearly not equipped to answer. You seem to agree on that as well. However, we disagree that that then means there can be no answer. There can be one, just not one which science can provide. As such, it may be a very personal answer, over which people can respectfully disagree, but it still can be a very real answer which is useful in informing people's lives, and upon which people may act. --Jayron32 21:29, 3 May 2010 (UTC)

Without evidence of any kind, the more normal word for "answer" is "guess". So sure, if we can't figure out what (if anything) caused the big bang - then we are at liberty to guess - but we shouldn't go around suggesting that this guess is of much value. That being the case, you might as well say that the universe was sneezed into existence by the Great Arklesiezure as that it came from a black hole in some older universe - or any other guess you might come up with. The trouble is that with a literal infinity of possible causes - all of which are equally probable - the odds of your guess being correct are essentially zero. SteveBaker (talk) 23:27, 3 May 2010 (UTC)

You are still confusing cause with purpose, and confusing the Big Bang with creation. There's no problem in concept with using science to discover the cause of the Big Bang. Again, it may not be possible due to the laws of physics, but the concept is sound. Discovering the cause of the universe doesn't add to my understanding of the purpose of the universe, or of my life. Knowing the details of the process that created me doesn't grant me any insight into the knowing the purpose for which I was created. Furthermore, even if a furtherback cause for the Big Bang were discovered, it wouldn't change the nature of "creation", it pushes the date farther back, if you will, but still doesn't answer the fundemental questions of creation itself. Changing the identity of the creation event doesn't eliminate the questions surrounding creation itself. I understand you don't spend much time pondering things of this nature, things like "purpose", but can you atleast concede that they are valid matters for human discourse and reason, and as such, there are going to be valid discussions regarding them, even if you yourself have no interest in such discussion? --Jayron32 14:39, 4 May 2010 (UTC)

Buddha said that creation was a false concept, that creators don't exist. Why should "nothingness" ever exist without somewhere there being something? 67.243.7.245 (talk) 20:33, 4 May 2010 (UTC)

Human centipede - possible in real life?

Apologies in advance if this question causes you to consider concepts that you'd rather not have considered...

In the movie The Human Centipede, the mad doctor character creates the titular outrage against nature by attaching three people together by their digestive systems (i.e. sewing person B's mouth to person A's anus, then person C's mouth to person B's anus - the idea being that it is then sufficient to feed only person A, with B and C being nourished by poop and second hand poop, respectively). Nasty, huh?

Now, the movie advertises itself as '100% MEDICALLY ACCURATE!' (granted, which may be one of those standard horror movie marketing things intended to further disturb the audience) and the director says that he actually consulted with a top surgeon to design a feasible series of operations by which the human centipede creation could be accomplished.

Question is this (for the medically-qualified here, mainly) - quite simply, would someone *really* be able to do carry this out in real life? If so, how long would the human centipede realistically be able to survive and what sort of medical complications might arise? I'd imagine that there would be a whole host of things that could go very badly wrong, very quickly.

I do hope that my question doesn't fall afoul of the RDs 'no medical advice' rule... :) --Kurt Shaped Box (talk) 12:24, 3 May 2010 (UTC)

Coprophagia ——but this not address the nutritional value to humans, which I suspect is inadequate. Graeme Bartlett (talk) 12:29, 3 May 2010 (UTC)

Just as an aside, I really was expecting that article to contain an user-created image of a man eating faeces. --Kurt Shaped Box (talk) 12:37, 3 May 2010 (UTC)

Apologies if you are a lady coprophagiac for the Male chauvinism exhibited by the above poster. Cuddlyable3 (talk) 20:58, 3 May 2010 (UTC)

As with many "based on a true story" films, there is no requirement for any claims the films make about their own accuracy to be true. Vimescarrot (talk) 12:51, 3 May 2010 (UTC)

The professional in the article you linked to mentions the necessity of an IV drip, essentially making the whole procedure redundant (you're just pointless making faeces go through two more digestive systems to no effect - you may as well attatch a fifty-foot tube to Person A's anus). Obvious complications would be the myriad diseases you can pick up from excrement (cholera is my first thought, there are dozens more) and, without an IV drip, malnutrition. Vimescarrot (talk) 12:58, 3 May 2010 (UTC)

The key phrase here is "based on" - meaning that they started with a perfectly normal story with nothing unusual or unexpected about it - and blew it out of all proportion. If you imagine a real-life doctor who did a study on the efficiency of the human gut and discovered (not unreasonably) that some percentage of nutrients remained on excretion. A movie "based on" that true story could certainly contain this much nonsense. Sadly, there are no legal requirements for the correctness of movie blurbs! SteveBaker (talk) 13:01, 3 May 2010 (UTC)

I bet there is some implied legal requirement for a movie advertisement to be accurate, as with other ads. If they put out a blurb for a movie claiming it's a kid's movie and it's really a porno, I think they could get in trouble, for instance. The movie Kindergarten Cop seemed close to that line, being advertised and titled as if it were a cute kid's movie, but actually being a violent movie no child should see. StuRat (talk) 13:09, 3 May 2010 (UTC)

(after ec)Thanks for the answers so far, guys. FWIW, I don't believe that it was ever stated that the movie is 'based on a true story' - just that the director asked a surgeon how *he* would go about sewing three people together, ass-to-mouth, if he was an insane doctor... --Kurt Shaped Box (talk) 13:10, 3 May 2010 (UTC)

Since most the nutritional value has been removed after the first run, starvation would be an issue for the 2nd person and even moreso for the third. A more realistic way to have one person medically feed others might be to splice their circulatory systems together, although this would require compatible blood types. If only one person was fed, they would then get hungrier, because much of the nutrition would be used by the other people. In this way, it might be similar to having a tapeworm. The other people, who would be denied food, would still be hungry due to an empty stomach, but might not starve, if enough nutrition was received through the shared blood. The person who does eat might eat 3x the normal food and still not gain weight. Have I just invented a new fad diet ? :-) StuRat (talk) 13:05, 3 May 2010 (UTC)

I haven't seen the movie, but the article on it seems to imply that the nutritional needs of the people are not met and that one of them begins to suffer from blood poisoning as a result of the arrangement. That sounds about right to me. Not only would the nutritional value of feces be very low, it would be full of all sorts of gut flora that is quite toxic to humans, and not nearly enough water to survive on. Person #2 in the conga line would probably get quite sick, which would probably mean that person #3 would get... less than nutritional byproducts as well. I think the centipede would not survive long—numbers 2 and 3 would probably get quite ill, and at the very least would dehydrate themselves. --Mr.98 (talk) 13:23, 3 May 2010 (UTC)

Source: "100% MEDICALLY ACCURATE" at 2:17 (video). The standard for Wikipedia is verifiability not truth. Cuddlyable3 (talk) 20:51, 3 May 2010 (UTC)

I'm a little surprised no one has mentioned E.coli.. I read once somewhere that even if you are starving to death, don't eat human poop. Bad effects will far outweigh any benefit. Vespine (talk) 22:43, 3 May 2010 (UTC)

Well, I did mention gut flora, the larger category of stuff in yer guts of which E. coli is a distinguished member... --Mr.98 (talk) 23:39, 3 May 2010 (UTC)

"Man-made global warming can cause volcanoes"

There was a documentary on C4 last night called "The Volcano that stopped Britain". Near the end they claimed that man-made global warming caused volcanos to erupt by melting the ice on top of them. How do they get away with spreading such nonsense? I like to think I'm pretty liberal but i've lost most of those views since seeing this. Aren't there laws against knowingly spreading lies?--92.251.130.74 (talk) 14:16, 3 May 2010 (UTC)

That's interesting, I was watching a program last night on National Geographic about the same volcano, and it spent a fair amount of time covering the mind boggling amount of ice that the volcano its self melted, though not nearly the amount of an event in I think 1996. Definitely seems like a major flaw in the program if they think man made warming could even approach the heating effects of a volcano. Beach drifter (talk) 14:30, 3 May 2010 (UTC)

Even if hte ice was melted, that wouldn't cause the volcano to spontaneously erupt would it?--92.251.130.74 (talk) 14:42, 3 May 2010 (UTC)

Perhaps it was a phreatomagmatic eruption, i.e. one pertaining to the contact between magma and water (from melted ice?) Regards, --—Cyclonenim | Chat  14:48, 3 May 2010 (UTC)

After reading several articles, it seems there are phreatomagmatic components to the eruption, but they are side effects due to the location, and not the cause. Beach drifter (talk) 14:54, 3 May 2010 (UTC)

I think the idea is that GW could cause ice sheets to melt, which causes post-glacial rebound which in turn could release pressure on volcanoes causing an eruption. I agree that its not really necessarily to scare monger like this with relation to GW - its bad enough as it is - but I guess it makes for exciting TV. 131.111.30.24 (talk) 16:03, 3 May 2010 (UTC)

Almost correct, but nothing to do with post glacial rebound (though both have the same cause). Awickert (talk) 17:40, 3 May 2010 (UTC)

(outdent) Removing ice sheets reduces the vertical confining pressure on a magma chamber, increasing deviatoric stresses and causing an eruption. This is also well-documented in a study in Iceland of lava flow volumes during the last deglaciation. To the original poster of this: if you've changed your views by calling something "nonsense" and "lies" without knowing what you're talking about, I suppose that's your call. Though I admit: modern-day documentaries can over-dramatize to the absurd, and sometimes bungle the facts, making skepticism natural. Awickert (talk) 17:40, 3 May 2010 (UTC)

(edit conflict) It's a real theory that melting glaciers can trigger eruptions due to decompressing active magma chambers. Basically, by removing the pressure of 100 m of ice (for example) you cause more of the superheated rock to melt and more gases to escape and this might cause an eruption to happen hundreds of years earlier than it would have otherwise. It is important to note that this is about triggering volcanoes and not causing them. Melting ice certainly doesn't cause a magma chamber to form. At best it might provoke an existing magma chamber into erupting a little bit early. It's not specific to global warming either, people argue about changes at the end of the last ice age triggering eruptions. Dragons flight (talk) 17:43, 3 May 2010 (UTC)

Even if that were true, the resulting eruption would be less explosive then it would otherwise have been, and therefore cause far less trouble then one that goes Krakatoa. Googlemeister (talk) 19:27, 3 May 2010 (UTC)

How do you know that? Awickert (talk) 19:57, 3 May 2010 (UTC)

Simple thermodynamics. If you have a pot on you stove filled with boiling water and place the lid on (for the purposes of this experiment you can assume this makes the inside of the pot airtight), as the water boils, it forms steam. Steam has a volume far larger then that of water, so without anywhere to go, the pressure increases. If the lid is lightweight, this pressure will force the lid up, and steam will escape and some water may boil out of the pot. Inconvenient perhaps, but not a catastrophe. If you make the lid heavy, or better yet, weld it to the pot, when failure finally occurs, the pressure differential will be far greater, and so will the damage. Googlemeister (talk) 20:42, 3 May 2010 (UTC)

Ah, OK. Thanks for your answer! Unfortunately, volcanoes aren't that simple, largely because there is no constant "burner" and the "lid" is both nonuniform in its material properties and evolving through time. So for example, with a heavier lid, the lava may freeze before it gets to the top, making less of an eruption. Or conversely, to bring in another issue, the eruption may be less damaging without the glacial lid because it won't trigger jokulhaups. (Also, as an aside, Icelandic volcanoes don't have the right composition to go Krakatoa...) So what you say is an interesting idea; when I get a chance I'll see if I can find anything published about it. But I would caution against making authoritative claims about complex systems based on simple models in the meantime (unless you do a little research and find out that you are indeed correct). Best, Awickert (talk) 21:00, 3 May 2010 (UTC)

OK - our OP needs to calm down and do the tiniest scrap of background research.

I don't see any problem (in principle) with the idea that (a) global warming melts glaciers and other ice deposits...which (b) reduces the pressure on the top of glacier-encrusted volcanoes...and (c) that it is possible that reducing the pressure on the top of the magma chamber of a volcano could trigger an eruption. Imagine a volcano that is just on the edge of having built up enough internal pressure so it's on the verge of exploding...just on the tipping point...then melting the glaciers could be enough to cause an eruption that might not otherwise have happened for another 100 or 1000 years. It might also change a slow oozing magma flow into a full scale explosion - as water from the melting ice could be flashed into steam inside the magma chamber, increasing it's ability to overcome the reduced pressure on top.

So this isn't nonsense (meaning non-sense) because it does actually make some kind of sense. I just don't know whether that's really what happened.

Whether that is specifically what happened in this case would require some considerable study. So I googled it. :-) It turns out that it's not just C4 the BBC who are saying this - this article in the Daily Telegraph newspaper claims the same thing. It turns out that their claim (and therefore, probably, C4's the BBC claim) is based on a study by the Royal Society who are a rather prestigious bunch of scientists.

Hence, I think our OP is WILDLY overreacting. C4 The BBC is most definitely not lying because a lie is a deliberate untruth - and they are only repeating what some extremely reputable scientists are saying. So it's not a lie. Channel 4 The BBC are doing their job - and in this case, they are doing it well...so quit complaining about that!

The guys at the Royal Society may be mistaken (a mistake is a non-deliberate untruth) - but they too are not lying. This is properly published, peer-reviewed work, in "The Philosophical Transactions of the Royal Society". That journal has been the gold standard for scientific reporting for 300 years (Sir Isaac Newton was published there!). So C4 the Beeb didn't say anything that's in any way unreasonable.

Now - if you wish to place your own extensive scientific training your privately obtained data and your own in-depth study into this subject matter against people who were published by the Royal Society - please feel free to do so...but don't expect us to be wildly sympathetic to your cause because the odds are very good that you're guessing! So, IMHO, you should assume that (like most BBC documentaries) this was well researched and based upon solid scientific sources. Certainly, the idea that there might be some law you could invoke is WAY out of the question!

SteveBaker (talk) 19:43, 3 May 2010 (UTC)

I thought it was channel 4 and not the BBC? C4 don't have the best track record on documentaries (The Great Global Warming Swindle springs to mind) so perhaps the OP was correct to be sceptical. 86.7.19.159 (talk) 19:58, 3 May 2010 (UTC)

I'm sorry - you're right. I'll fix my response. SteveBaker (talk) 20:39, 3 May 2010 (UTC)

Using the phrase "I like to think I'm pretty liberal but..." suggests the OP considers the issue a political not a vulcanological one.Cuddlyable3 (talk) 20:09, 3 May 2010 (UTC)

And if this were the rabid right-wing politics reference desk, I'd have answered accordingly...but since this is science - and AFAICT, they nailed the science perfectly - we have to take an appropriately offended stance. SteveBaker (talk) 20:39, 3 May 2010 (UTC)

Dare I suggest, Steve, that a more effective approach would be to explain what the paper suggests would happen, without the command to take it as verbatim truth because it's from the Royal Society. I think you'd be more persuasive if you yourself didn't seem so defensive about it, and if the alternative you offered was more varied than "take it on faith because of who said it". I don't think responding to a polarized view with an even more polarized view generally accomplishes much. Just my two cents. --Mr.98 (talk) 23:34, 3 May 2010 (UTC)

You mistake what I'm saying. The question before us is: Was Channel 4 lying (as our OP so vociferously alleges) when they said that this global warming theory is a true possibility? No!! Clearly they were not lying because (like Wikipedia and other responsible journalists) they relied upon 'reliable sources'. Nobody can seriously doubt that one of the oldest and most respected scientific journal on the planet is a reliable source!

Now, it might be that there is an error in the paper in that journal - nobody claims that their peer-review system is infallible. Or it might be that the journal (for some utterly bizarre reason) faked the entire thing and there is a gigantic secret conspiracy. But what we cannot doubt is what Channel 4 said. They reported results from a reliable source...they absolutely, 100% certainly, did not lie. If the documentary is wrong (which seems really unlikely under the circumstances) then Channel 4 is not to blame. They can't even be accused of making a mistake...they honestly reported a reliable source - and that's the very best we could hope they'd do.

As for the Royal Society - for sure, they occasionally make mistakes - no journal is ever 100% infallible. After all, we had 200 years of everyone reporting that Newton's Laws were right - then Einstein came along and proved them all (very slightly) wrong. But given the choice - and given that you aren't a vulcanologist - should you believe your own guesses about how volcanoes work? Or should you believe a paper published in one of the most respected journals in the world? By all means be skeptical - by all means dig out the paper and read it yourself - but PLEASE don't go off on a major rant about some Channel 4 documentary without at least some sort of evidence beyond "gut-feel".

SteveBaker (talk) 00:45, 4 May 2010 (UTC)

Regarding Aren't there laws against knowingly spreading lies? No - OFCOM decided that it is outside of their remit to punish broadcasters over the accuracy of their programs - see this, only news reports have to be factually accurate. 131.111.30.21 (talk) 12:24, 4 May 2010 (UTC)

Internal and external cell conditions - source?

I need to find a source (preferably in table form but I can always form one from the data) which provides cell conditions for Na+, Ca++, Cl- and K+ ions with respect to their concentrations internally and externally? Anyone know of such a source? Regards, --—Cyclonenim | Chat  15:50, 3 May 2010 (UTC)

Articles Nernst equation or Resting potential may help. Cuddlyable3 (talk) 17:02, 3 May 2010 (UTC)

Membrane potential also would be useful. The lede mentions all 4 ions. See also ion channel and Ion transporter and Plasma membrane Ca2+ ATPase and Na+/K+-ATPase. Cytosol#Ions discusses actual concentrations, and has a handy chart that lists difference between intracellual concentrations and blood concentrations. Extracellular fluid has some figures as well, though not in a handy chart. --Jayron32 18:19, 3 May 2010 (UTC)

Supporting ladder on stairs - sideways

I need to position a ladder on some stairs, sideways so that it leans against the wall at the side of the stairs. The stairs are eight inches deep, but the ladder is about 15 inches wide. Thus one foot of the ladder will dangle unsupported.

What is the best practical way to support the ladder firmly and safely? The stairs are not very wide either, and are covered in carpet. Thanks 92.28.253.63 (talk) 16:31, 3 May 2010 (UTC)

You'll need to find a device which extends the leg of the ladder on the downstairs facing side. Something like this, but I'll let more knowledgeable people give you advice on specific products. Note that this stabilises the ladder to the usual extent like it would on the floor, but particular care should be taken not to wobble the ladder whilst you're on it. Regards, --—Cyclonenim | Chat  16:34, 3 May 2010 (UTC)

Cut out a big block of wood and fix it to the lower stair, although obsiouly in a maner which you can remove it.--92.251.141.43 (talk) 16:40, 3 May 2010 (UTC)

In a professional setting, those needing to carry out work on stairs usually construct a scaffolding platform, as I myself have seen done on several occasions while employed in facilities maintenance: indeed, in the UK it is contrary to Health & Safety Regulations to carry out actual work more than 2 metres above the ground from a simple ladder, which should only be used for access and inspection; also, ladders should always be secured in place at top and bottom (the latter can be done by a workmate rather than mechanically). What an individual chooses to risk doing in a private setting is, of course, up to him/her, but you may wish to balance the worth of your intact neck against the cost of getting the job (whose specific setting, scope and duration we do not know) done by a trained professional.

As an alternative to both a straight ladder and to constructable scaffolding (i.e. tubes, clamps and boards), you might be able to buy, or more economically hire, a small mobile scaffold tower with the two sides adaptable to different base heights supporting a horizontal working platform, which are designed for this sort of work: I suggest you make enquiries at a local equipment hire firm, if you can find one. 87.81.230.195 (talk) 19:18, 3 May 2010 (UTC)

Buy a ladder like this one. Then you put the ladder sideways like this. You can get different sizes for that ladder, and there are other brands, which might be less expensive. Ariel. (talk) 21:03, 3 May 2010 (UTC)

No liability whatsoever is assumed by providing this information, but I have seen painters wishing to work on the wall high above a short run of stairs place a ladder against the wall at the bottom of the stairs, then run a scaffold or plank from the ladder to a step at the same level. See "How to use a scaffold on stairways."An old 1906 solution in Popular Mechanics is seen here and some modern solutions are shown http://books.google.com/books?id=RTC8yFaw7ioC&pg=PA32&dq=ladder+stairs&lr=&as_brr=3&cd=6#v=onepage&q=ladder%20stairs&f=false here]. Some modern ladders are made with the two sides independently adjustable as Ariel pointed out. Edison (talk) 21:38, 4 May 2010 (UTC)

Moment of Inertia

My textbook says that moments of inertia about principal axes are constant to the first order for small angular displacements. Is there any way to prove this? Thanks. 173.179.59.66 (talk) 16:53, 3 May 2010 (UTC)

Wikipedia's relevant articles are Moment of inertia and List of moments of inertia. A consequence of the definition of the Sine of an angle x (in radians)

${\begin{aligned}\sin x&=x-{\frac {x^{3}}{3!}}+{\frac {x^{5}}{5!}}-{\frac {x^{7}}{7!}}+\cdots \\[8pt]\end{aligned}}$

is that for small x

${\begin{aligned}\sin x&=x\end{aligned}}$ approximately. Cuddlyable3 (talk) 19:59, 3 May 2010 (UTC)

Great, thanks. 173.179.59.66 (talk) 23:59, 3 May 2010 (UTC)

(edit conflict) Cuddlyable3 is deriving the Small-angle approximation, an often used approximation in physics, and quite accurate for small angles: i.e. an error of less than 0.15% for angles smaller than 5 degrees, about 0.5% for angles smaller than 10 degrees, and still only about 5% for angles up to 30 degrees (yeah, you have to convert to radians when working with it...) Buddy431 (talk) 00:07, 4 May 2010 (UTC)

Don't worry, I understood. Actually, I was aware of the small angle approximation. I just realized that I was using addition when I should have been multiplying. —Preceding unsigned comment added by 173.179.59.66 (talk) 02:29, 4 May 2010 (UTC)

Alcohol for stage fright

Is alcohol an effective treatment for stage fright? Are there any other non-prescription drugs that are as good as or better? Thanks 92.28.253.63 (talk) 17:19, 3 May 2010 (UTC)

Wikipedia cannot offer medical advice. Alcohol is not a prescribed treatment for any known medical or psychological condition. If you are having trouble, please seek advice from a qualified professional, such as a psychologist, who works in this field. The internet, and random strangers that hang out there, is not the proper place to ask such questions. --Jayron32 18:13, 3 May 2010 (UTC)

How is stage fright a condition needing medical advice? I intensely dislike preforming in front of people, but it doesn't require a "qualified professional" to treat. Ks0stm ^(T•C•G) 18:29, 3 May 2010 (UTC)

Stage fright isn't a medical condition - but as soon as someone starts to ask us to suggest drugs to treat it - it becomes a request for medical advice...and our only answer is "If this concerns you - go see a doctor." In this case, it's possible that a doctor might prescribe something. SteveBaker (talk) 19:08, 3 May 2010 (UTC)

I'm not suffering from stage fright, and I do not like alcohol. I was asking in general terms, not medical advice. 92.28.253.63 (talk) 18:23, 3 May 2010 (UTC)

In that case, I reiterate that Alcohol is not prescribed for any known medical or psychological condition. Some people self-medicate using alcohol, usually to less-than-desirable results (alcohol-related violence, cirrhosis, drunk driving, addiction.) Anxiolytic are the class of drugs prescribed for anxiety problems, which stage fright certainly qualifies. None are actually availible over-the-counter, unless you count "herbal" remedies, or "off-the-label" remedies. --Jayron32 18:29, 3 May 2010 (UTC)

That is not strictly true. Ethanol is occasionally prescribed for poisoning by ethylene glycol or methanol. The latter two substances are very toxic, but not terribly toxic in themselves — rather, the damage is done by their metabolites. Ethanol competes for the enzyme that oxidizes or dehydrogenates them, giving the kidneys a chance to eliminate the substances before the toxic metabolites can be formed. --Trovatore (talk) 23:21, 3 May 2010 (UTC)

What you are describing is a result of abuse or over-consumption of alcohol. You can get nasty results if you overdose on pretty much any other chemical, from cough syrup (toxic psychosis), vegetable oil (Cardiac Arrest) or even water (Water intoxication). Googlemeister (talk) 19:23, 3 May 2010 (UTC)

I'm sorry, people have never abused alcohol before. Statistically speaking, there is not a significant number of people to have every overconsumed alcohol to even mention. I apologize for misleading people to thinking that there are ever negative consequences from using alcohol to excess. (as an aside, I am not a teatotaller. I regularly consume responsible amounts of alcohol.) --Jayron32 19:42, 3 May 2010 (UTC)

I'm not going to say anything about its effectiveness, but alcohol is very frequently used for such things. See Dutch courage. --Tango (talk) 19:24, 3 May 2010 (UTC)

So you are going on stage and feel nervous? Then Break a leg !. Cuddlyable3 (talk) 19:36, 3 May 2010 (UTC)

A well-known symptom of alcohol intoxication is the loss of social inhibitions, so it's reasonable to assume that stage fright would be reduced. However, whether the lack of stage fright would outweigh the decreased mental capacity caused by alcohol and make the show better overall, I can't say. --99.237.234.104 (talk) 20:08, 3 May 2010 (UTC)

However, we should not be advising people to treat an anxiety disorder by drinking. Such irresonsible medical advice is exactly what the medical disclaimer is about. Yes, people do drink because they have anxiety. However, to recommend that as a reasonable course of action, to actually state "Yes, it would be a good idea to drink alcohol to combat stage fright" is a fantasticly irresponsible thing to do. If anyone is seeking genuine advice on how to handle stange fright or any other anxiety disorder, see someone who knows how to treat anxiety disorders. Period. --Jayron32 20:28, 3 May 2010 (UTC)

I hardly think it's proper to call stage-fright an "anxiety disorder". This medicalisation of normal feelings is a pernicious trend in late 20th and early 21st century western society. I'd ask an actor or an acting coach for advice about stage fright. DuncanHill (talk) 21:04, 3 May 2010 (UTC)

I didn't advise anybody to do anything. My answer was a scientifically valid statement of well-known facts. --99.237.234.104 (talk) 21:12, 3 May 2010 (UTC)

I agree. "Anxiety disorder" means being anxious about things a normal person wouldn't be anxious about. Almost everyone is anxious about appearing on stage in front of hundreds of people. --Tango (talk) 22:37, 3 May 2010 (UTC)

Before trying this, be sure to watch The big bang theory episode The Pants Alternative (the link has a small spoiler, don't click on it). Ariel. (talk) 21:18, 3 May 2010 (UTC)

If you've gone a way down the path to becoming an actor then you have contemplated the awesome responsibility of addressing an audience from a stage. That you continued along this path probably indicates that you've worked "stage fright" into the equation of what you bargained for. It is unlikely that the fear of going onstage only cropped up at the last minute. You can take heart from your own decision, made time and time again in preparation for your role as stage actor, that this is something that you calculate you can do. Bus stop (talk) 21:31, 3 May 2010 (UTC)

For discussion of the "piss artist" in acting see [12]. There is a danger that an actor may feel he is doing his best work, when his fellow actors and the audience see someone whose timing is off, who muffs lines and stumbles around. Even one instance of showing up tipsy for a public performance can stick for a lifetime, as happened to Andrew Johnson at his vice presidential inauguration. Edison (talk) 21:29, 4 May 2010 (UTC)

construction, coal

During excavation for a new house, a seam of coal was uncovered. will the coal hold up to a foundation placed on top or is it too soft and will require pilings drilled through the seam and filled with rebar and concrete? It will be a large house and the foundation for the fireplace will be close or on the seam. thanks for any help on this. —Preceding unsigned comment added by Lhirsche (talk • contribs) 18:43, 3 May 2010 (UTC)

Really? You want to ask people on the internet about how to safely build your house? The answer almost certainly depends on the size, extent, and type of deposit. You need to talk to a structural engineer, geologist, or someone similar who can inspect the site and give you a professional evaluation. Dragons flight (talk) 18:52, 3 May 2010 (UTC)

There are lots of different foundation approaches for modern houses. No matter the type of soil or subsurface conditions, you'll need a proper foundation design. So even if there had been no coal there - you'd still be crazy not to have someone design you a proper foundation that's appropriate to the conditions. Specifically, I'd expect coal to be a pretty good rock to build onto - but if an expert says otherwise then there are other options beside the 'pier and beam' approach you are describing. My house is build on some of the soggiest clay imaginable with the bedrock 30' below the house...we have a floating 'waffle slab' that floats on the soil...and that's despite it having foot-thick concrete walls! But you have to consult an expert - the consequences of a foundation/slab failure can be utterly catastrophic. SteveBaker (talk) 19:05, 3 May 2010 (UTC)

There is more then one type of coal, from bituminous to anthracite. They would not have the same structural properties, so expert help is strongly recommended. Googlemeister (talk) 19:14, 3 May 2010 (UTC)

How convenient to have a coal mine under the fire place. What could possibly go wrong? Edison (talk) 19:48, 3 May 2010 (UTC)

Do you live in Centralia, Pennsylvania? Googlemeister (talk) 20:25, 3 May 2010 (UTC)

Just in case you are simply looking for a second opinion, and not actually relying on random people on the internet to build your house, coal is pretty strong and you should be able to build on it. I'd worry about gases being released from the coal though. Methane, and Radon specifically. Radon especially is pretty bad, be sure to handle it properly, either active venting, or some sort of construction technique to make sure it doesn't enter the basement. Also, you may have legal issues. In many parts of the country, you don't own mineral rights under your land, so that coal may not be yours, and I have no idea what that would mean to your house. If it is yours see if it's worth mining that coal (well, selling it to a mining company) instead of building on it. Ariel. (talk) 23:29, 3 May 2010 (UTC)

I doubt if mining the quantity of coal that would be found on a typical house lot would be cost effective. StuRat (talk) 00:21, 4 May 2010 (UTC)

My understanding is that coal mining often starts by finding a seam on the surface, then following it underground. The bulk of the coal is underground, and not limited to the size of a house lot. Ariel. (talk) 00:35, 4 May 2010 (UTC)

Sure, but what's the advantage to you if they pull up coal from your neighbor's yard? APL (talk) 03:13, 4 May 2010 (UTC)

I don't think it's necessarily a non-profit endeavor to extract coal from a neighbor's yard -- there was an answer on this topic posted some time ago, but it's certainly profitable to extract coal even if you have to pay others for the coal you get from under their property. DRosenbach ^{(Talk | Contribs)} 16:48, 4 May 2010 (UTC)

I don't know if you can build a house on it (see a licensed architectural engineer), but I do know you can build a house from it: Coal House (Williamson, West Virginia). -- 174.21.225.115 (talk) 15:30, 4 May 2010 (UTC)

Wouldn't it be a fire hazard? 146.74.230.104 (talk) 00:24, 5 May 2010 (UTC)

how much is $280,000 per year (inflation-adjusted) for 40 years worth today?

How much is $280,000 per year, but adjusted for inflation, ie this value goes up from year to year to account for inflation, and to be paid out for 40 years, worth today? Thank you. 84.153.250.110 (talk) 19:30, 3 May 2010 (UTC)

Do you mean, how much would being paid $280,000 per year, adjusted for Cost of living annualy, be worth if the first $280,000 payment was made 40 years ago? Or do you mean that you are going to be paid #280,000 this year, and want to know what the COLA payments will do to the money over the next 40 years? I am unclear on what you are asking. --Jayron32 19:35, 3 May 2010 (UTC)

Numerous websites will calculate the inflation adjusted values of money, a simple Google search will find them for you. This one shows that $280,000 in 1969 was equivalent to $1,620,160 in 2009. TastyCakes (talk) 19:38, 3 May 2010 (UTC)

Future inflation cannot be predicted. 40 x $280 000 = $11 200 000. Cuddlyable3 (talk) 19:41, 3 May 2010 (UTC)

Well it can be predicted, it just can't be predicted correctly ;) TastyCakes (talk) 19:45, 3 May 2010 (UTC)

Of course, even if you had a true figure, most people time discount; that is, they'd take 90% of something this year than 100% of it next year (rightly or wrongly). So it might be "worth" more or less today than it is in the future, depending on how you look at it.- Jarry1250 ^{[Humorous? Discuss.]} 19:56, 3 May 2010 (UTC)

If it's adjusted for inflation - then isn't the answer just $280,000 x 40 ? SteveBaker (talk) 20:11, 3 May 2010 (UTC)

If the question was asked correctly, then I agree, that's exactly what it is. Vimescarrot (talk) 20:28, 3 May 2010 (UTC)

The question above (which is different from the one below) asks for today's value of a stream of payments of $280K (adjusted for expected inflation) paid annually for 40 years. Even though inflation is adjusted for, you also have to adjust for the time-value of money. So the answer will be lower than $280K x 40, unless the discount rate is equal to (or less than) the expected inflation rate - but there would be no sense in using a discount rate like that. Zain Ebrahim (talk) 11:49, 4 May 2010 (UTC)

Um, I'm the original questioner and your answers don't make sense to me. Let's simplify and say that you will be paid nothing until 40 years from now, at which point you will be paid the then-equivalent of $1,620,160 in today's dollars. How much would you pay for that to happen? Obviously it has to be far LESS than a million, since why would you tie your money up for 40 years for nothin'? What I want to know is exactly how much less. I think it has to do with the prime rate. This isn't homework.... 84.153.250.110 (talk) 20:54, 3 May 2010 (UTC)

That's actually impossible to answer. Inflation is a very tricky thing, people have a very hard time agreeing on what historical inflation has been, that is how to calculate inflation based on what we know has happened to values over the past 40 years. To predict with any certainty what will happen in the next 40 years is literally an impossibility. Inflation has little to do with the Prime rate. The Prime rate is part of monetary policy which is the means by which central banks hope to control inflation. Inflation itself is measured in very different ways; see producer price index and consumer price index for a couple. If anyone definitively knew how to predict inflation reliably, they'd be fantasticly rich. --Jayron32 21:21, 3 May 2010 (UTC)

No, he said it was the then-equivalent of $1,620,160 in today's dollars, which means 84.153 has removed inflation from the equation. In this revised question, 84.153 is asking what would be a good price for a fixed rate bond which matures 40 years from today for the then-equivalent of $1,620,160 in today's dollars, issues no coupon payments, and is not callable. I am going to venture an answer, based on the current price of 30-year TIPS bonds that sold about a month ago for 2.125%. If we use this as the answer, then your answer will be somewhere under US$720,000 (because you're selling a 40 year instrument instead of 30). The main critical assumption I am making here is that your bond would be backed by the US government and not some company; else a higher interest rate would be demanded. Comet Tuttle (talk) 21:29, 3 May 2010 (UTC)

mm if I'm reading this right, is this now a net present value/time value of money question? If it is, the net present value will depend on what discount factor you use, and that's really up to you. You could use the historical average of a big bond rate like Comet Tuttle says above, or you could use the average stock market growth over the last 50 years, or the average inflation rate or any number you think represents how much more money in your pocket right now is worth than money maybe in your pocket next year. TastyCakes (talk) 21:42, 3 May 2010 (UTC)

Yes, it sounds like a time value of money question. The challenge with these questions is working out an appropriate discount rate. --Tango (talk) 22:41, 3 May 2010 (UTC)

Yes — and 84.153 also didn't specify whether this bond can be sold to another party. If not, and you're already 70 years old and in poverty, there may not be any appropriate discount rate, because you may not want to tie up even $1 in a scheme that will not pay off during your lifetime. Comet Tuttle (talk) 00:02, 4 May 2010 (UTC)

This restated question becomes a question of what interest rate you can earn versus how inflation grows. If you can get an interest rate that consistently out-paces inflation, then take the money now - and invest it. If inflation out-paces interest rates - then let someone else pay the price and take the money in the future. Which of those things wins is utterly unknowable. It depends on how interest rates change - how the stock-market grows (or shrinks) - how much risk you're prepared to take. That last thing is the real problem. Historically, the stock market grows about 5% per year and the inflation rate isn't that high for long. So the stock market ought to be a no-brainer...except for risk. As a lot of people have recently discovered, there is not such thing as a safe stock. Who knows what happens to the major markets of the world over the next 10 years - let alone the next 40! Uncertainly increases exponentially with time. So, we can't reliably answer your question. Risk is the big issue here. If you want to take the money and invest it now - and you expect a 99% chance of beating inflation - then you're forced to take such low-risk choices that you can't make any money. If you only want a 50/50 chance of beating inflation - then you can probably find a set of stocks that will give you a 50/50 chance of winning big-time over inflation. So if you are risk-averse, take the money in 40 years and let whoever is paying it to you take all of the risk. Of course if the person/organization/government who is supposed to do that fails over the next 40 years then you may be completely screwed - so there is no such thing as a 0% risk. SteveBaker (talk) 00:14, 4 May 2010 (UTC)

Here are some thoughts for determining a discount rate. Assuming you give the money to an insurance company, you can use the following sum:

Required return = real risk-free rate + credit-risk premium + liquidity-risk premium

• Risk free rate: You can use Comet Tuttle's suggestion above for the first part: 2.125% (these are ususally quoted as nominal rates).
• Credit premium: Look at the long term (e.g. 10-year) credit spread on highly rated insurance companies. Insurance companies don't typically issue very long term debt so you can also look at banks that might have issued 30 or 40 year bonds.
• Liquidity might not be an issue for you if you don't intend to sell this. There are many many ways to try and estimate this - if you're interested, you can try google.
• You don't need to add anything for inflation if you assume that whatever you get in 40 years will compensate you for whatever inflation did over that period.
• There may be other special circumstances that you would need to allow for.

Then just add them up and discount at that rate. Alternatively, insurance companies sell this kind of product all the time - just call your local insurance broker and ask him how much this would cost. Zain Ebrahim (talk) 12:27, 4 May 2010 (UTC)

Nothing

In the bits of space between the molecules, atoms, ions, &c., do forces still apply? What exists in the space between them in which gravity, magnetism and so on exist to allow the potential forces to exist. I suppose what I am asking is what nothing is, or what 0 actually means. If you could suck all the matter completely out of a given area does it still exist because there is no matter in it to describe it? -russ (talk) 19:54, 3 May 2010 (UTC)

Gravity, magnetism and other such forces are not transmitted by real physical particles that require a "something to exist between here and there" to work. DMacks (talk) 19:59, 3 May 2010 (UTC)

It was once thought that a medium called the luminiferous aether was required to transmit the electromagnetic force, but this idea was incorrect. The gravitational and electromagnetic forces propagate just fine through a vacuum. -- Coneslayer (talk) 20:00, 3 May 2010 (UTC)

There is almost nothing between the stars and planets - but the force of gravity still operates perfectly well. Gravity can be shown to operate between galaxies too - and the space between them has so little 'stuff' in it that we're down to one atom per cubic meter or so! So clearly forces can operate through a vacuum. On a smaller scale, the strong and weak nuclear forces operate at the scale of individual atoms - and (as you say) the atoms are separated by a nice, hard vacuum. The earth's magnetic field is responsible for deflecting charged particles from the sun - and that too operates out beyond our atmosphere - so you can tell that magnetic forces also propagate just fine through "nothing". SteveBaker (talk) 20:18, 3 May 2010 (UTC)

For people that have a problem with forces propagating through nothing, there's field theory. Fields are by no means necessary to explain or understand force propagation through empty space (see Action at a distance), but they do provide a helpful framework for understanding how things like "light waves" propagate through empty space (i.e. Q: "what" is vibrating in a light wave? A: the electromagnetic field). Insofar as concepts like "energy" are "real" so are fields. --Jayron32 20:25, 3 May 2010 (UTC)

But doesn't that mean that a vacuum must exist, which according to Wikipedia is 'only a philosophical concept and never is observed in practice'? -russ (talk) 20:12, 3 May 2010 (UTC)

Well, I don't have much time for philosophers - they cause more confusion than they do clarity. The question here is whether you should have a name for nothingness. A 'vacuum' is defined as the absence of matter - does that make it a useless concept? Not at all, it's an exceedingly handy word - and for beings who live in a world surrounded by air, the concept of a 'vacuum' is sufficiently different from normal existence that it makes sense to have a word for it. Beside, we use 'black' to mean an absence of light - and 'silence' to mean an absence of sound - are those also "only philosophical concepts"? SteveBaker (talk) 20:22, 3 May 2010 (UTC)

(also reply to pierhead above, EC with him below) Vacuum is an asymptotic condition, not a philosophical concept. Science is filled with concepts which are physically impossible to achieve, and yet are very real, such as absolute zero, big bang, speed of light, etc. etc. Being impossible to achieve is not the same as saying its only a "philosophical concept". Things like ontology and eschatology and epistemology are philosophical concepts. A vacuum is a very real, if physically unobtainable, condition. --Jayron32 20:37, 3 May 2010 (UTC)

Classically, you can have real, hard vacuum. Out there between the galaxies there is only about one atom per cubic meter of space. If the atom happens to be in the top-left corner of that cubic meter - then you have almost an entire cubic meter of perfect vacuum. However, from a quantum-theoretical viewpoint, there are two problems with that. One is that fundamental particles don't have exact positions - they are probability clouds - so even if the atom is nominally considered to be in the top-left corner - there is a vanishingly small probability that you'd detect it over a meter away in the bottom-right corner. In a sense, the atom is everywhere at once - so no place in the universe is truly empty. Beyond that, you have the issue of virtual particles where a particle and an anti-particle will pop up out of nowhere - then vanish again just as fast - and this makes it tricky to define precisely what we mean by "empty". Also, there would be a lot of photons and neutrinos out there too...so if you count those, then there is quite a lot of 'stuff' contained in that cubic meter. SteveBaker (talk) 23:04, 3 May 2010 (UTC)

Does not the absence of sound and light constitute an entity in which they are void? The void must surely still exist as those properties which propogate them still exist and are absorbed by their terminal entities? Is there, therefore no (realistic) nothing or zero? -russ (talk) or am i just being needlessly foolish? —Preceding undated comment added 20:34, 3 May 2010 (UTC).

I think you're confusing the existence of stuff with the existence of a concept to describe the situation. "Vacuum" is a concept that exists, even though nothing exists in a vacuum. That's not contradictory. We can label any concept we want. But more importantly, this is a philosophical issue that doesn't have much to do with understanding the science. Rckrone (talk) 21:39, 3 May 2010 (UTC)

May 4

learning skills

On one of the Nat Geo documentaries that I watched, I saw why one messes up when they get nervous. It seems that there are two parts of the brain that learns a skill. One is a learner that is very clumsy and a learned part that executes the technique. When one needs to perform and cannot overcome their nervousness, the very clumsy "learner" part takes over and the resulting performance is bad. I think they used an amateur soccer player for this experiment and tricked him by saying that he was being watched by talent scouts. Anyone can direct me to its wiki article? --121.54.2.188 (talk) 00:39, 4 May 2010 (UTC)

I've never heard this idea before and am very sceptical. It doesn't make much sense to have your brain learning something twice, once not very well. We have an article on Anxiety and also the Yerkes–Dodson law which may be useful to you. --Tango (talk) 02:20, 4 May 2010 (UTC)

I think I wasn't very clear. One part of your brain learns the skill while the other part executes the learned skills. Anyways, it seems to be Procedural memory and messing up due to choking. I was able to get to them from muscle memory.--121.54.2.188 (talk) 02:26, 4 May 2010 (UTC)

(edit conflict)Its probably closely related to concepts like working memory vs. short-term memory vs. long-term memory. The article The Magical Number Seven, Plus or Minus Two specifically discusses on theory of Working memory and also contains some great links to related articles. I think there is a specific term related to this sort of performance-learning connection. As a teacher, you'd think I remember the term. I'll do some digging and get back to you. --Jayron32 02:22, 4 May 2010 (UTC)

The article Procedural memory also discusses learning procedures and processes, and the normal way in which procedures are learned. May offer some insight into the OP's question. --Jayron32 02:27, 4 May 2010 (UTC)

Molar mass of Aluminium

What is the molar mass of Aluminium? Thanks in advance, --The High Fin Sperm Whale 01:45, 4 May 2010 (UTC)

It is in the article, in the infobox, under the title "Standard atomic weight". --Jayron32 01:59, 4 May 2010 (UTC)

dumbest idea in the world

So this has to be the dumbest idea in the world, but please confirm that it is. They have done various nuke tests in the desert where after the bomb goes off, the sand underneath is fused into glass, maybe dozens of feet thick. The dumb idea is: what if they do that underwater, as a way to seal the burst oil well in the gulf of Mexico? Would it exchange one environmental catastrophe for another? Radiation, tsunamis, etc.? Test ban treaty issues? There was at least one deep-water test in the 1950's (Operation Wigwam) whose effects weren't all that severe. 69.228.170.24 (talk) 01:57, 4 May 2010 (UTC)

Would the explosion fuse the sand into glass, or would it rupture the entire oil deposit, and send the entire contents of the deposit into the sea instantly, making the situation MUCH worse. Its a nice line of thinking, but beware of unintended consequences. --Jayron32 02:01, 4 May 2010 (UTC)

I think most of the heat would go into evaporating the water, rather than melting the sand. --Tango (talk) 02:06, 4 May 2010 (UTC)

Controlled frac is done all the time during drilling and enhanced oil recovery. It never needs nuclear weapon sized explosions. Most of the time, just pumping saltwater or steam down the bore is sufficient to frac the entire formation. In some cases, chemical frac (chemical fracture) is used - e.g., injecting an acidic drilling mud to intentionally break up the reservoir rock. Frac often increases permeability, rather than decreasing it - though the geomechanics is very complicated and depends on the circumstances. See, e.g., Hydro Frac at the Schlumberger oilfield glossary. Blowing stuff up in the borehole will more likely increase fluid flow; but there's a possibility of plugging the hole. Remember also that there's a pressure gradient - the oil is flowing up because it is at higher pressure than the water (and the rock) above it. That is why it blew up in the first place. Nimur (talk) 02:23, 4 May 2010 (UTC)

FYI the technical term for intentionally plugging the well to stop fluid flow is "bridging" the borehole. Nimur (talk) 02:32, 4 May 2010 (UTC)

You might find this article a good description of the likely consequences. Clear skies to you 67.170.215.166 (talk) 02:48, 4 May 2010 (UTC)

I can't believe I forgot to link to Completion (oil and gas wells). This is the term for the general set of techniques to manage a well, including casing, cementing, safety valves, and so on. I don't believe any completions use explosive of any type. Most use downhole tools and careful control of fluid/mud pumping. Nimur (talk) 14:39, 4 May 2010 (UTC)

Apparently it's not such a dumb idea, because if this article can be believed, the russians actually used nukes 5 times to seal leaks. Ariel. (talk) 19:59, 4 May 2010 (UTC)

For what it's worth, the article is from the Komsomolka, which is every bit as credible as our own National Enquirer. 67.170.215.166 (talk) 01:46, 5 May 2010 (UTC)

refrigerating foods

I have heard from some people that refregerating some foods spoil them.Is it true?amrahs (talk) 04:24, 4 May 2010 (UTC)

Never heard that before. See Refrigerator for details. There are some issues, such as freezer burn if meat is not packaged properly before freezing. Additionally, if the fridge is not cleaned properly, food may become contaminated through a process known as "cross contamination". But a properly maintained fridge and/or freezer should be perfectly safe for all foods, so long as the foods themselves are properly packaged before storing. --Jayron32 04:39, 4 May 2010 (UTC)

Actually, some foods will indeed spoil, not in the sense of becoming contaminated or rotten but in the sense that they will turn into something I wouldn't want to eat. Bananas, for instance become pretty disgusting when placed in the refrigerator. Dauto (talk) 04:45, 4 May 2010 (UTC)

Generally speaking, foods with a high water content (like bananas) are susceptible to "freezer burn" -- since water expands on freezing, any ice crystals that form tend to burst the cell membranes and thus degrade the food item's texture. Likewise, if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In both these cases, however, the items involved are still safe to eat (though less appetizing). Foods made from grain, though, tend to have a different problem if refrigerated -- since they have very low inherent moisture content, they tend to exhibit hygroscopic tendencies at near-freezing temperatures, which makes them soggy and also could promote mold growth. (Incidentally, I store bananas in my fridge all the time, and I hardly ever observe any degradation in texture from it.) FWiW 67.170.215.166 (talk) 04:57, 4 May 2010 (UTC)

Correction: the phenomenon I described where ice crystals burst the cell membranes is not the same as freezer burn -- the latter is caused by dehydration from contact with the air. 67.170.215.166 (talk) 05:01, 4 May 2010 (UTC)

Not really refrigeration as much as freezing but an interesting fact is the founder of the modern method of freezing food was Clarence Birdseye, founder of the Birds eye company. Until I discovered this I always assumed "Bird's eye" was just a arbitrary name. Vespine (talk) 05:52, 4 May 2010 (UTC)

Potatoes and other foods that are rich in starch will go off faster in a 'fridge than at room temperature. The temperature promotes the conversion of starch to sugar. CS Miller (talk) 11:08, 4 May 2010 (UTC)

Not correct. Warmth drives the starch to sugar conversion, not cold; cold temperatures put the spud into hibernation. Potatoes actually have a longer shelf life when kept near 0C (Please don't just take my word for it, but I do work in a huge foodservice distribution centre where we routinely have to store hundreds of different products to maximize shelf-life.) The problem with taters in the fridge is that they are not kept uniformly chilled; every time you open the door, you introduce more warm air and humidity and this fluctuation is what kills the spuds. If you have potatoes that you're planning on using, keep them cool, dry, and dark - slightly less than room temperature if you can. If you want to keep them for more than a couple of weeks, keep them cold, dry, and dark (you know, like in a root cellar), just let them warm up before you try to make fries with them.

It doesn't have anything to do with starch to sugar conversion, but certainly breads and other baked goods don't keep as long cool. Refrigerating breads causes them to go "stale" faster. (Staling in breads has more to due with rearrangement/recrystallization of the gluten network, rather than drying out per se.) Freezing baked goods, on the other hand, doesn't have the same problem. Cookwise and Bakewise by Shirley Corriher are good reads, if you are interested in the topic. -- 174.21.225.115 (talk) 15:25, 4 May 2010 (UTC)

You're right, placing fruits and vegetables that are grown in warm regions into the fridge damages them. It is due to their plasma membranes being susceptible to chilling. Basically the membrane stops being a fluid and turns into a gel, this creates holes in the membrane allowing the cell contents to mix. This is obvious with bananas as they go black but it also happens with tomatoes (and others - not sure which). It's not due to ice crystals forming as 67.170 says. Temperate fruit + veg are used to the cold and so are preserved by the fridge - their membrane lipids are less saturated and longer, so the Van der Waals forces between the lipid tails are weaker and the membrane remains fluid and intact at lower temperatures. 131.111.30.21 (talk) 12:34, 4 May 2010 (UTC)

See Banana#Storage_and_transport - it might only be when they are unripe that the fridge damages them. Also see Tomato#Picking_and_ripening - they remain edible but lose their taste when refridgerated. 131.111.30.21 (talk) 12:41, 4 May 2010 (UTC)

Chilling also causes decreased binding of ethene to its receptor, thereby slowing down ripening as well ([13]). It looks like this may also be the same in tomatoes. 131.111.30.21 (talk) 12:56, 4 May 2010 (UTC)

Note - "if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In ...these cases, however, the items involved are still safe to eat" - is not true.

"The third and most important reason not to refreeze is increased risk of spoilage due to microorganisms. Many people thaw food by letting it sit at room temperature for several hours, giving the microorganisms in it time to get busy and partially spoil the food before it's refrozen. The problem is particularly pronounced in large pieces of meat such as a turkey, some parts of which may be at or near room temperature for hours during thawing. That's why turkeys should be thawed in a sink filled with water--the water equalizes the temperature and makes for faster thawing. Alternatively, you can thaw in the refrigerator, which is slower but retards spoilage by keeping the meat cool. Even so you're likely to have some multiplication of microorganisms. If you refreeze and rethaw, you've subjected the food to double the microorganism growth and double the fun.

If you must refreeze food that has been thawed in a warm place (or which has remained thawed in a cold place for a long time), you should cook the food properly first, then refreeze it. Even under the best circumstances, however, multiple freezing cycles aren't recommended. If you can't finish the food yourself, you're better off giving it to your household garbage disposal--ideally the one that barks or meows."[14] Exxolon (talk) 16:06, 4 May 2010 (UTC)

Ice cream that's been allowed to warm to a few degrees above freezing and then refrozen is no more dangerous than the food in your fridge. Clearly warmer is worse than colder (up to room temperature) but lets be reasonable. Rckrone (talk) 16:27, 4 May 2010 (UTC)

"Refrigeration" is not the same as "freezing." The OP did not ask about the freezer. Bananas turn dark quickly in the refrigerator, but refrigeration is claimed to leave them edible longer[15]. Some books claim that refrigerating tomatoes [16] and avocados [17] adversely affects the flavor and texture . A refrigerator is kept in a range of perhaps 34 to 38 degrees F (1-3 C). A freezer might be at 0 degrees F( -17C).A "self-defrosting" freezer causes worse freezer burns than older manual defrost ones, because of the low relative humidy needed to remove the frost from the walls. Edison (talk) 21:11, 4 May 2010 (UTC)

Tomatoes and bread are two things that tend to suffer from refrigeration -- tomatoes turn mealy, and bread dries out. Looie496 (talk) 00:55, 5 May 2010 (UTC)

Air navigation

What is an aperiodic compass, and how does it work? I've seen it mentioned by both Amelia Earhart and Charles Kingsford-Smith in their writings, but neither of them explains in any detail how it works or what advantages it has (if any) over an ordinary magnetic compass, Earth inductor compass, directional gyro or any other such device. Also, is it still used for navigation, or has it been completely replaced by other devices? Thanks in advance! 67.170.215.166 (talk) 05:12, 4 May 2010 (UTC)

Aircraft are very different to ships in that they can change heading rapidly, so ideally an aircraft compass can retain a reasonable degree of accuracy during a turn, without excessive overshoot. Prior to development of the gyroscopic compass, many aircraft were equipped with a magnetic compass specially developed for use in aircraft. This was more complex than the simple magnetic compass used for surface navigation. It was called the aperiodic compass. There is some good information available HERE. In modern aircraft the magnetic compass is used primarily as a back-up for the gyroscopic compass, and to ensure the gyroscopic compass is correctly aligned. Consequently, in modern aircraft the magnetic compass is simple and inexpensive because it is not relied on when maneuvering.Dolphin (t) 05:49, 4 May 2010 (UTC)

I wouldn't call the magnetic compass a "backup". It's the reference for the gyro, which has no sense of direction of its own. The gyro is set to the mag compass on the ground, and checked periodically when it level flight. It is, as you say, used for navigation and maneuvering, because it's easier to read and interpret that the mag compass. PhGustaf (talk) 06:19, 4 May 2010 (UTC)

So essentially it's a magnetic compass with an advanced magnetic damping system that prevents oscillation and overshoot (but also makes it lag behind the aircraft when maneuvering); and there's no longer any need for it because the gyrocompass is the primary instrument when maneuvering. Thanks for the info, and clear skies to you! 67.170.215.166 (talk) 06:14, 4 May 2010 (UTC)

I wasn't clear. All the gyro can do is point the same way all the time, with a little drift and precession. It has no idea which way is north. So the pilot sets it so it's pointing North, or whatever direction the magnetic compass says. The mag compass is the primary direction reference. The gyro has a bigger dial and is easier to interpret if the aircraft is turning, because is isn't sensitive to second-order issues, as is the mag compass. You mostly watch the gyro and check every so often to make sure it agrees with the mag. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

I would imagine magnetic compasses on aircraft these days are electronic, e.g. using flux gates or other such devices. 69.228.170.24 (talk) 20:23, 4 May 2010 (UTC)

Could be. My pilot's license dates from 1976, and I might have missed stuff since. But even a plane with a flux gate compass would surely have a mag compass along: it doesn't weigh much, works even when the electric system fails, and doesn't break often. Modern pilots use GPS a lot. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

It isn't correct to imagine that modern magnetic compasses in aircraft are electronic. If a modern general-aviation aircraft has a magnetic compass it will only be for orienting the gyroscopic compass. It wil be of the basic variety as used in boats, not even an aperiodic one. (Modern aircraft of the highly sophisticated jet-powered variety are likely to have no magnetic compass. Modern Inertial Reference Systems, GNSS and area navigation systems render the humble magnetic compass redundant.) Flux gates are linked to the gyroscopic compass to keep it aligned correctly - they are not linked to the magnetic compass.

Back to the original question. I believe the word aperiodic was intended to refer to the expectation that the compass needle would not follow the aircraft as it maneuvered but would remain accurately in the north-south alignment. Dolphin (t) 01:33, 5 May 2010 (UTC)

That is what Dolphin51's link says. According to it, an aperiodic compass is a magnetic compass like a ship's compass, but with better damping to keep the needle from swinging erratically.

As for highly sophisticated jet aircraft having no magnetic compass and instead relying exclusively on R-NAV, personally I find it extremely disturbing -- what if there's a total electrical failure? Or if lightning strikes the plane and fries the electronics? On some aircraft, all electronics are powered by engine-driven generators without any battery backup worth the name, so if there's a double-engine failure then all the electronics fail too and the pilot has no way to determine his/her heading. Didn't the Air France disaster teach the designers anything? It's high time that the pilots got together and demanded more stand-by instruments in the cockpit as well as full manual backup for all the primary flight controls! 67.170.215.166 (talk) 02:00, 5 May 2010 (UTC)

shadows, mirror images?

Are shadows mirror images? Are they superimposable? At times, i noticed the images of shadow and mirror being alike, for ex.: a word printed on a glass shows shadow (behind the glass)similar to that of the original (not reversed) and similar image is also seen when a mirror is placed behind the glass on which the word is written. Hope i am clear..- anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 05:15, 4 May 2010 (UTC)

No, shadows are caused by an object blocking light rays, while a mirror image is caused by light rays reflected from the object being reflected a second time by the mirror. FWiW 67.170.215.166 (talk) 05:36, 4 May 2010 (UTC)

Regarding your second question, shadows are not actual things. A shadow is a place where there is less light - but it isn't no light at all. There is still some light, but less. If you have a second shadow on top of the first, then you have even less light then before. Ariel. (talk) 06:17, 4 May 2010 (UTC)

If you're facing the writing on the same side as the light source, the shadow looks "normal" (i.e. you can read it easily). The mirror on the other side of the glass shows you the mirror image of the other side of the writing (i.e. the inverse of the inverse) so it looks the same as the shadow. This doesn't mean that the shadow is a mirror image - but in this case they are superimposable. Hope this helps. Zain Ebrahim (talk) 13:07, 4 May 2010 (UTC)

FORTRAN Programming (Lahey Compiler)

I am trying to run one old fortran program (1980's). I compiled it using Lahey Compiler and i removed all errors and warnings. It is not running properly, if i give some print or write commands at some particular locations in some subroutines, it starts running. I am not able to understand without making any change in the code how is it running just due to some print or write commands and the results are still some what away from expected.203.199.205.25 (talk) 07:12, 4 May 2010 (UTC)

You will probably find a more receptive audience at WP:Reference desk/Computing. I suggest you delete your message from the Science Reference Desk and paste it into the Computing Reference Desk. Dolphin (t) 08:16, 4 May 2010 (UTC)

Cross-posted at Computing desk. Nimur (talk) 12:14, 4 May 2010 (UTC)

is it HF that kills? or F-?

I'm a little confused by the articles. Is F- toxic because it can form HF, or is HF toxic because it can form F-? Ignoring acidity, which is the more toxic species here? Is it because F- is a potent nucleophile, or binds with Ca2+ to form calcium fluoride? John Riemann Soong (talk) 07:26, 4 May 2010 (UTC)

It looks like the F- reacts with the Ca++ to form CaF2, but the H+ in the HF seems to function as a carrier ion (it carries the acid into the skin); even though any F- (or fluorine gas) is toxic in itself. --Chemicalinterest (talk) 11:05, 4 May 2010 (UTC)

see Fluoride#Toxicology F- is 'mildy toxic' and poisonous by hypocalcemia at relativly high doses. Hydrogen fluoride causes burns - in addition to any toxicity caused by flouride present.

In both cases the 'solution' is Ca2+ ions (ie as calcium gluconate / hydroxide / chloride) to precipitate F- as CaF2.

HF is more toxic because it both burns and poisons.77.86.70.220 (talk) 11:35, 4 May 2010 (UTC)

Is fluoride really a potent nucleophile? It holds on to its electrons tightly, so I don't think it's very happy to donate them to electrophiles.

Ben (talk) 00:17, 5 May 2010 (UTC)

The peculiar thing about F- is that although it indeed holds on tightly to its electrons, it has a high charge/size ratio because of its small size, which causes it to bind irreversibly to both calcium and magnesium to form insoluble salts. Living cells can't function without either, so they die off. This is why HF can cause such deep burns -- it soaks into the skin due to the action of the H+ ion, and the F- ion then kills the cells by precipitating the calcium. (Which is why the folks at our alkylation unit have to wear neoprene coveralls at all times while on duty.) 67.170.215.166 (talk) 02:08, 5 May 2010 (UTC)

An additional effect is that HF isn't a strong acid, so it doesn't necessarily cause serious "acid burns" (only 1-2 pKa units stronger than acetic acid I think). But because it's not highly ionic, it would be more able to penetrate skin and other water-tight membranes. So the H+ assists getting the HF in, where F- then can do some serious damage. Glacial-acetic poured on your hand? Wash it off right away, will be red/itchy for a few hours. Dilute HF few drops on your hand? You're in for a world of hurt for a long time. DMacks (talk) 02:18, 5 May 2010 (UTC)

Are Kepler's laws rigth?

Hi, I hope this is the rigth corner to open this discussion.So I copy-pasted my former talk from other wikicorners.I claim:

Planetary orbits are not elliptical,but spiraled,with the Sun at the barycenter.Newton's universal attraction force formula F=G*M*m/r^2 gives the masses a tangential velocity so that each masses have to orbit one around the other (attraction force=centrifugal force). This tangential velocity Vp is constant:Vpm for m and VpM for M until the masses reach to the barycenter.Kepler says the contrary. According Kepler the tangential velocities are variable and the areal velocities are constant.But,when you draw the polar graph of two bodies you find, according Newton's F*dt=m*dV,the motion's equation r=-a*t*(t-tmax) which shows no sign of ellipse.No ellipse,no focus,no aphelion,no perihelion,nor equality of swept out areas in equal interval of time.Consider Nasa's photos of the galaxies: you will see the spiraled orbits of celestial bodies.Newton does not confirm Kepler; except for period's law (P1/P2)^2=(r1/r2)^3 which is valid only and only for circular orbits.Does Kepler has changed his reasoning;(elliptical orbits in 1609 and circular orbits in 1618)? Yes.He wanted to say, the elliptical orbits will be transformed to circular orbits with time.How does a solid elliptical shape could be transformed to circular shape,unless the orbits are not elliptical? This is possible when the orbits are spiraled: expanding and then compressing, billions of spirals. TASDELEN (talk) 07:35, 4 May 2010 (UTC)

Think about conservation of energy and see how your proposal fits in. Graeme Bartlett (talk) 10:22, 4 May 2010 (UTC)

Kepler's laws are simplified, empirical observations that are valid to a certain level of accuracy for certain cases that are valid to describe planet-like orbits. I don't follow your description about spirals; but in any case, there are other types of orbit, including non-elliptical orbits (such as those of a non-returning comet, or the orbit of a ballistic missile, which intersects the planet it orbits). These cases require mathematical treatments using the more general laws of Newtonian gravitation (and eventually, general relativity's even more complete description of gravitation). Your polar-form equation of planetary motion is not correct in the general case - I'm not sure where you got that equation from, but it looks kind of like an equation for a parabolic orbit - only one of many possible paths. Kepler's laws are applicable only if the orbit is closed and unperturbed. Our articles are extraordinarily descriptive of all possible cases. Nimur (talk) 12:22, 4 May 2010 (UTC)

TASDELEN, you are mistaken. Kepler's laws are completely consistent with Newton's law's within the "two body problem" approximation - That is, provided any pertubations introduced by other planets are negligible. Dauto (talk) 14:40, 4 May 2010 (UTC)

Coefficient of drag at hypersonic speeds

Hi,

I was wondering how C_D varies with Ma at hypersonic speeds? Must graphs of C_D I have seen only go up to Ma 2.0, I'd like to know how it varies up to Ma 20 (eg what the Falcon Hypersonic Technology Vehicle experiences). Thanks! --58.175.32.19 (talk) 08:36, 4 May 2010 (UTC)

At hypersonic speeds, the linear model described in drag coefficient is totally inapplicable, so there's no real need for these charts. The shape and geometry become significantly more important than the total effective surface area. This is why an aerospike reduces drag, even though it adds surface-area exposed to the fluid flow. Consider this paper, Numerical Solution of the Hypersonic Viscous Shock-Layer Equations (AIAA, 1970). Nimur (talk) 11:31, 4 May 2010 (UTC)

Newton's cradle question

I recently bought an inexpensive Newton's cradle. Much to my dismay, it is not operating as nicely as I had expected. When the outside ball hits the remaining four, the middle three do not stay perfectly still, they wiggle quite a lot - and very quickly start swinging back and forth. This causes the motion to deteriorate very quickly. If I start by putting two balls into motion, it is even worse. Are there any simple adjustments that can be done to improve it? Thanks, decltype (talk) 10:19, 4 May 2010 (UTC)

Make sure that the row of balls is precisely in a straight line. Should be able to adjust the supporting cords. Graeme Bartlett (talk) 10:24, 4 May 2010 (UTC)

Curvy tunnel

On Balfour Beatty's website there is a tunnel image http://www.balfourbeatty.com/bby/segments/business-intro/ - ( Image url ) can anyone identify what project this is from, and what the tunnel is for?

More importantly - can someone explain why the tunnel is so crazily curved - is this trick photography or real. Thanks. Sf5xeplus (talk) 10:59, 4 May 2010 (UTC)

Balfour Beatty's website gives a contact e-mail address. Have you tried asking them about the tunnel? Cuddlyable3 (talk) 12:05, 4 May 2010 (UTC)

No I haven't contacted them.Sf5xeplus (talk) 13:41, 4 May 2010 (UTC)

The convoluted nature, the lack of a flat foor, and the diameter, would suggest it was for carrying water. It looks like a pipe inside a hydroelectric power plant, or a pumped storage plant like Dinorwig Power Station. These typically feature wire-bore tunnels for water to pass through, either for power generation or as part of the overflow system (see these pictures for the Hoover Dam's overflow tunnels). That said, every tunnel of that nature I can find pictures of has a smooth surface (either concrete or stone). Balfour Beatty does just that kind of business, but then they do lots of large civils in general. -- Finlay McWalter • Talk 14:17, 4 May 2010 (UTC)

I was wondering about sewage (google images show some similar page 4 and 5 - but most are smooth) - The shape doesn't make a lot of sense - appears to be a S bend followed by a turn to the right - more suitable for a water slide - anyone think the image has been distorted? Sf5xeplus (talk) 15:03, 4 May 2010 (UTC)

I'd suggest that it's the pedestrian part of an underground railway station, without the floor. Bank Underground station has at least one tunnel which is essentially the shape shown, with a staircase on the bit that's not horizontal. AlexTiefling (talk) 00:13, 5 May 2010 (UTC)

Addendum: although I can't be certain, I'd suggest that it might be the new access tunnel leading to the Northern Line platforms at Kings Cross St Pancras. AlexTiefling (talk) 00:34, 5 May 2010 (UTC)

Gloria Allred

Question moved to Wikipedia:Reference_desk/Miscellaneous#Gloria_Allred

substitute for peanut butter

I initially became a big nutritional fan of peanut butter when I read that it had no cholesterol and twice the protein of calves liver. Boy was I excited - peanut butter the perfect food. Then I started gaining weight only to realize 40 lbs later that even though peanut butter had no cholesterol it had plenty of fat. Not only did it have fat but it had saturated fat but alas I could not stop eating the stuff because I also loved the taste. Now my doctor says stop eating peanut butter or die so I have to find a substitute. What tasty treats with unsaturated oil can I find that will take the place of squshed gubbers? 71.100.1.71 (talk) 15:52, 4 May 2010 (UTC)

ask your doctor. Dauto (talk) 15:56, 4 May 2010 (UTC)

I did and he said that for a longer list to consult the Wikipedia. —Preceding unsigned comment added by 71.100.1.71 (talk) 15:58, 4 May 2010 (UTC)

All right then. Here's my suggestion: Eat more fruits and vegetables andexercise more frequently. Dauto (talk) 16:17, 4 May 2010 (UTC)

While finding an unsaturated fat alternative is probably better, the real problem here is that consuming excessive fat whether it's unsaturated or saturated is likely to increase your weight, simply because fat's energy density is so much higher than protein/carbs. You need to find an alternative that's both lower in saturated fat and lower in calories! Exxolon (talk) 15:59, 4 May 2010 (UTC)

The calorie thing is under control by limiting myself to 11 grams of peanut butter per meal (3 meals per day) for a diet plan of 21% fat, 67% carbs and the rest protein. So what unsaturated substitutes do you suggest? 71.100.1.71 (talk) 16:12, 4 May 2010 (UTC)

Typing the words "peanut butter substitute" into Google returned this search result: [18]. There's lots of options. --Jayron32 16:18, 4 May 2010 (UTC)

LOL... I told my doctor that when I asked the Wikipedia they said to Google. 71.100.1.71 (talk) 17:19, 4 May 2010 (UTC)

I was surprised to find almost instantly a link to waht is being called "soynut butter". I guess this idea already took off due to peanut butter "allergy's". 71.100.1.71 (talk) 16:55, 4 May 2010 (UTC)

• However, in comparing the labels of great value brand peanut butter and peanut free soynut butter the soy actually fairs worse with 14% instead of only 10% saturated fat and 4 grams of sugar instead of only 3. 71.100.1.71 (talk) 17:12, 4 May 2010 (UTC)

Why the " " on "allergys"? 86.178.228.18 (talk) 21:20, 4 May 2010 (UTC)

You eat peanut butter with every meal? One of the key features of a good diet is that it be varied, otherwise it is easy for it to be deficient in something (there are plenty of nutrients that you only need a small amount of but that aren't in all foods, eating lots of different foods means you will probably be eating at least one with each of the essential nutrients in it). --Tango (talk) 17:30, 4 May 2010 (UTC)

Ignoring the obvious problems involved with a diet high in any fat, I personally enjoy SunButter. It has multiple varieties, which are more or less similar in taste to a comparable type of peanut butter. That said, it still has saturated fat, about 2/3 the amount in peanut butter. And its overall fat content (saturated plus unsaturated) is close to peanut butter. —ShadowRanger ^(talk|stalk) 17:17, 4 May 2010 (UTC)

To be clear, there are a whole lot of varieties of SunButter, and the similarity to peanut butter varies. Natural Crunch is the only one I buy regularly (I like crunchy over creamy), and it's a very close match (a little sweeter and less oily to my taste). I can't say how close the other varieties are to their equivalent peanut butter. Also, if I didn't make it clear, the primary ingredient in SunButter is sunflower seeds plus some sugar. —ShadowRanger ^(talk|stalk) 17:20, 4 May 2010 (UTC)

I suggest you try either "organic" or "natural" peanut butter. In both cases they won't contain the added trans-fats, which make it creamy, and will have somewhat lower saturated fats, too. Without that it will separate and need stirring, but that's a small price to pay for avoiding trans-fats. You might wonder why the label says 0 trans fats on traditional creamy PB. They just keep the amount low enough that they are allowed to "round down" to zero. In the US, anything under 0.5 gram can thus be classified as 0, even though getting that much trans fat in every serving is unhealthy. Look for partially and/or fully hydrogenated vegetable oil in the ingredients, that means they added trans-fats. StuRat (talk) 17:33, 4 May 2010 (UTC)

As a side note yes I am aware of the round down problem which Congress can eliminate by requiring all nutrients be stated as grams per 1000 versus grams per serving and then let the customer do the serving math. 71.100.1.71 (talk) 18:54, 4 May 2010 (UTC)

Focusing on saturated fat for weight loss is simply wrong. It won't help in the slightest. Saturated far affects cardiovascular health, but not weight. And switching to unsaturated fat for cardiovascular health is also wrong. Because the ratio of the various types of unsaturated fat matters (the various Omega types) too. And cutting fat out entirely won't help either, because aside from being bad for you because you need essential fatty acids, carbohydrates can be converted into fat by the body. If you really do want to fix your health then for starters stop eating sweetened peanut butter, switch to unsweetened (it's harder to find though). Second stop eating a lot of any one food. There are some foods that historically have worked as the main source of calories (staples), but most are not suited for that. Ariel. (talk) 19:44, 4 May 2010 (UTC)

Even with lots of available variety, the problem of staples is taste. People have a tendency to eat over and over again only the tastes they like. 71.100.1.71 (talk) 20:20, 4 May 2010 (UTC)

Meteorological deposition of carbon dioxide snow or frost

Seeing as the coldest temperatures on earth (eg Vostok Station) are often well below the freezing point of carbon dioxide, do these areas see deposition of solid carbon dioxide from the atmosphere, such as CO2 snowfall or frost? If not, why not? —Preceding unsigned comment added by Btxtsf (talk • contribs) 16:39, 4 May 2010 (UTC)

The CO2 content of the atmosphere (around 0.05%) is so low that the snow probably would be unnoticeable. And the size of the miniscule amount of CO2 would decrease much more when solidified, since solids are generally smaller than gases. --Chemicalinterest (talk) 16:51, 4 May 2010 (UTC)

But, on the other hand, you get very little traditional snow there, due to the low water vapor content in the air, so any dry ice would therefore be a larger component of the total. An interesting Q, I wonder if you can easily tell the difference between the two. StuRat (talk) 17:45, 4 May 2010 (UTC)

An easy way to tell the difference: water snow feels wet in your hand, CO₂ snow doesn't. Clear skies to you 67.170.215.166 (talk) 02:13, 5 May 2010 (UTC)

Fill a Teflon sample bag with CO2 and seal it and the Vostokians may see some, but otherwise no. As to the 'why'. That has already been answered elsewhere, so I'll just link to it.[19]--Aspro (talk) 17:49, 4 May 2010 (UTC)

Vostok Station is over 11,000 feet above sea level, giving an atmospheric pressure only about 2/3 of the sea level value. That's enough of a difference to drop the sublimation temperature of CO2 by at least a few degrees, meaning that the sublimation point has never been reached in recorded data even there. Looie496 (talk) 00:49, 5 May 2010 (UTC)

Chemical element lists

I'd like lists for the following:

1) The state of matter (gas, liquid, solid) of each of the 118 chemical elements at STP.

2) The names from which the chemical symbols are derived, for those which are not derived from the English name. For example, W = Wolfram = Tungsten.

I could eventually figure them out by reading all 118 articles, but I hope lists are already available. StuRat (talk) 17:53, 4 May 2010 (UTC)

List of elements by name, List of elements by boiling point, List of elements by melting point might help.--Stone (talk) 18:02, 4 May 2010 (UTC)

List of chemical element name etymologies should help with 2 ? —Preceding unsigned comment added by 77.86.70.220 (talk) 19:49, 4 May 2010 (UTC)

Just to note, you are only going to find state-of-matter information for about 100 or so of the elements. Many of the largest elements have only existed briefly as a very small sample, sometimes of as little as a few hundred atoms; far too small a sample to say anything reliable about its "state". --Jayron32 19:55, 4 May 2010 (UTC)

Also, the heaviest elements are either named after famous scientists, or not named at all yet. Clear skies to you 67.170.215.166 (talk) 02:16, 5 May 2010 (UTC)

PhD programs and mental health

Can a PhD program be harmful to your mental health?--Mr.K. (talk) 17:57, 4 May 2010 (UTC)

Most academics would deny it, while a lot of PhD students would say that they suffered mentally during their slave work like thesis.--Stone (talk) 18:04, 4 May 2010 (UTC)

I'm not sure that most academics would deny it. Most that I know (which is many) would say, "yes, of course." They might say it is worth it (they might not), they might say it weeds out the less fortified (but they might also think it weeds out the non-crazy, as well). Academics are surprisingly straightforward about how crappy their overall career system is, even if they at the same time are likely to be less straightforward about whether or not that implies that academia is not all it is cracked up to be. Just my anecdotal experience. --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Can anything be harmful to your mental health? Yes. It is hard to attribute it specifically to a PhD program. Consider my PhD experience. I worked full time as a software engineer. I was raising two babies. I had to teach up 80 students (including grading homework and exams). I had to write not only a thesis, but also a readiness paper. I was also pestered with attending one symposium after another. Basically, I had about 30 hours of responsibility each day for about 3 years. So, did the PhD program cause mental health issues or was it the kids or dealing with idiots as a software engineer or dealing with students who claim their grandmother died three times each semester or simply never getting more than 4 hours sleep per day (and not 4 hours of continuous sleep)? I don't think you can blame the PhD program itself. It is an entire lifestyle that easily contributes to poor mental health. -- kainaw™ 18:11, 4 May 2010 (UTC)

There has been suicides of graduate students ,for example Jason Altom. How closely this is connected to his supervisor was disputed and will never be known.--Stone (talk) 18:14, 4 May 2010 (UTC)

As an addendum, I thought it important to point out that I believe my experience of three months of boot camp in the Marines was far easier than any particular 3 month period of my PhD program. It doesn't take much to mindlessly follow orders. However, being able to mindlessly do tasks until they are done does help a great deal when you have something like 80 programs to grade, each submission about 20 pages of source code, and you would much rather be doing anything else other than read through tons and tons of code that doesn't compile, doesn't make sense, and looks like random snippets of code pasted from various websites. -- kainaw™ 18:16, 4 May 2010 (UTC)

The answer is of course yes, as can school, the army, work etc... PhD's are notorious for their stress-levels (not for everyone of course) - WP:OR and it's quite suprising the percentage of PhD students who express a hate for their supervisor, or a deep unhappiness with the process..

In particular the transistion from primarily taught courses to self propelled is a factor, as it will be also the first experience for many of truly individual responsibility for their actions.

There's some results under http://www.google.co.uk/search?hl=en&ei=gXvgS5C3KJuTsQauqYzoBA&sa=X&oi=spellfullpage&resnum=0&ct=result&cd=2&ved=0CAYQvwUoAQ&q=phd+student+stress&spell=1 —Preceding unsigned comment added by 77.86.70.220 (talk) 19:56, 4 May 2010 (UTC)

One possible form of stress release for suffering grad students is write a comic strip. 69.228.170.24 (talk) 20:27, 4 May 2010 (UTC)

Yes, that is generalizable. (rolls eyes) --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Being in a Ph.D. program can be stressful, and stress can "harm your mental health." Being up for tenure can be stressful, too. Trying to get admitted to a good college can be stressful, as can trying to "do more with less" in the deliberately stressful environment of a large (or small) business, where years invested in a career can suddenly go "poof" due to corp reorg. I would expect that being in a modern war or occupation zone is rather more stressful. Being unemployed or underemployed is pretty stressful. I would not rate a PhD program as being the highest stress level I have encountered. Edison (talk) 21:05, 4 May 2010 (UTC)

You have to consider your initial susceptibility, general stress level, and lifestyle choices. If you're already inclined to depression or anxiety, for example, even the stress of high school or undergraduate university work might be enough to induce a full-on crisis. A person who is trying to juggle single parenthood, a full-time job, and graduate work is probably going to have a harder time of it emotionally than someone who has no major responsibilities and nothing else to do but concentrate on academic work. Knowing how to manage your time and how to de-stress yourself is an important factor. And making the right lifestyle factors is crucial, especially if you're already susceptible or stressed in the first place. Eat good healthy meals, get plenty of sleep, exercise regularly, have a supportive social network, and try to find time for things you enjoy, and you'll give yourself the greatest chance to get through a Ph.D. program - or college admissions or unemployment or almost anything else - with your sanity intact. 71.104.119.240 (talk) 01:08, 5 May 2010 (UTC)

HTPB

Our article on Hydroxyl-terminated polybutadiene says it is a polymer of butadiene terminated at each end with a hydroxide radical. So does the reaction to make it go like this?

nC₄H₄(OH)₂ → nH₂O + (C₄H₄O)_n

Also, do the all the C₄H₄ have oxygen between them? Thanks, --The High Fin Sperm Whale 19:20, 4 May 2010 (UTC)

The Os are at the end only (if in between it would be a polyether).

One synthesis uses hydrogen peroxide [20] US patent 5159123

The link probably has much of the answers you want.

The wikipedia article Hydroxyl-terminated polybutadiene incorrectly described it as a polyol - I've corrected that. —Preceding unsigned comment added by 77.86.70.220 (talk) 19:47, 4 May 2010 (UTC)

So do you use C₄H₆ and H₂O₂? --The High Fin Sperm Whale 20:10, 4 May 2010 (UTC)

Any radical initiator should work to start the polymerization reaction. --Jayron32 21:30, 4 May 2010 (UTC)

It needs to be convertable to OH - hence why H2O2 is used.77.86.70.220 (talk) 23:02, 4 May 2010 (UTC)

So are the bonds C-C? --The High Fin Sperm Whale 00:57, 5 May 2010 (UTC)

Yes they are. 67.170.215.166 (talk) 02:17, 5 May 2010 (UTC)

Gravity

Let's imagine I'm riding my bicycle in a frictionless world. Taking into account the following:

a) If I'm riding forwards on a completely flat road, I'll have to fight no gravity force at all (exactly 0 g), since gravity only hinders upward movement.

b) If I try to ride up a 90º wall, I'll have to fight all of the gravity force (exactly 1 g), since all my efforts will be directed towards movind upward.

Therefore, if I am riding up a 18º climb, I'll have to fight exactly 0.18 g, and if I am riding up a 23º climb, I'll have to fight exactly 0.23 g. Is that correct, or is my reasoning flawed? If so, what is the mistake? Thanks.

Leptictidium (mt) 19:32, 4 May 2010 (UTC)

The first mistake, surely, is that if 0º = 0g, and 90º = 1g, then 18º = 18/90 rather than 18/100. --Tagishsimon (talk) 19:34, 4 May 2010 (UTC)

I think force due to gravity = mgsinθ might be of use here. sin 90 = 1 and sin 0 = 0, but sin(18) degrees is not 0.18 (it's closer to 0.3, I think). - Jarry1250 ^{[Humorous? Discuss.]} 19:36, 4 May 2010 (UTC)

Not sure where this line of questioning is leading, but no, you can't even ride a bicycle on a flat road without friction. DMacks (talk) 19:38, 4 May 2010 (UTC)

What about a rocket powered bicycle? A kite attachment? A gun to fire backwards? - Jarry1250 ^{[Humorous? Discuss.]} 19:41, 4 May 2010 (UTC)

The OP is missing the necessary trigonometry to calculate the gravity force vector relative to the direction that he is traveling. I think Jarry1250 has it, you need to take the sine of the angle relative to the ground to get the portion of gravity you have to combat. --Jayron32 19:46, 4 May 2010 (UTC)

And, for completeness, you should consider the normal force of the incline. Without friction, you will experience a horizontal force, because the normal force is perpendicular to the incline, and only its vertical component is canceled by gravity. The remaining horizontal component will cause you to slide. Most often, that horizontal force is counterbalanced by static friction. Nimur (talk) 19:49, 4 May 2010 (UTC)

Sorry, yes, that was a lapsus and I was thinking along those lines. My question can be summarised as whether the force of gravity one must fight is directly proportional to the angle on which one is moving. Leptictidium (mt) 19:52, 4 May 2010 (UTC)

It is proportional to the angle in a sense. If you make a triangle such that the base is flat (zero degrees) and the angle you are riding is the hypotenuse, the height of the triangle is the amount of "upward travel" that will be fighting gravity in your example. You use trigonometry to calculate the length of the height based on the angle. Assuming that the hypotenuse is set to a length of 1, sine of the angle is the length of the height of the triangle - which is the amount of upward travel. -- kainaw™ 20:03, 4 May 2010 (UTC)

I've tied riding a bicycle on ice, which is a bit like the OP's problem statement. In a frictionless world, the driven wheel will spin without providing any forward motion whatsoever when you operate the pedals, so if stationary you will remain stationary, and if in motion you will remain in motion. You will not be able to accelerate or brake. Second, due to a lack of traction, the instant the center of mass is not directly over the center point of the line connecting the points of contact of the tires with the ground, the tires will slide sideways dumping you on the ground. Steering will not correct the condition, as it does in normal bike riding, even if you are moving forward. Any gyroscopic effect of the spinning tires is negligible (unless you get the the driven wheel spinning very fast indeed). The only ability to climb an incline would be due to the initial forward motion, since there is by definition no traction. Edison (talk) 20:53, 4 May 2010 (UTC)

"Can't Burn Your Skin"

i aw this

http://www.amazon.com/CERTOL-INTERNATIONAL-LLC-USA-128-1/dp/B000KKQ8LA

how can they say "Can't Burn Your Skin," —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:46, 4 May 2010 (UTC)

That description isn't for the Muriatic acid (hydrochloric acid is the more formal name), its for something called "Acid magic" , which is described as buffered hydrochloric acid. See buffer solution for a description of what a buffer is and what it does. I can't find a full ingredients list anywhere; the best I can find is that its a "proprietary blend". Here is an FAQ about the product: [21]. --Jayron32 21:14, 4 May 2010 (UTC)

Here's a forum discussion on it http://www.troublefreepool.com/acid-magic-as-an-alternative-for-muriatic-acid-t16607.html it doesn't look like anyone has an answer. Ariel. (talk) 21:36, 4 May 2010 (UTC)

As the FAQ says to always use gloves and goggles when using it, and they also insist on good ventilation, it doesn't look like they have much confidence in their non-burning non-fuming claims. DuncanHill (talk) 01:52, 5 May 2010 (UTC)

The buffer is prob'ly a weak base such as ammonia or an amine of some sort. But c'mon, if the acid's supposed to be strong enough to do its job instead of HCl, it's gonna be strong enough to burn your skin -- that's just a fact of life, deal with it. 67.170.215.166 (talk) 02:21, 5 May 2010 (UTC)

Digestive Cycles

I've read on several websites that the human digestive process follows a specific cirdadian rhythm that has three distinct phases. The appropriation cycle begins around noon (in most people) and continues until 2000 (8 pm). During this time the body is naturally predisposed to dispense plenty of energy to the digestive tract, and a person is most likely to feel hungry (the body's way of indicating it's the right time to take in food). The assimiliation cycle lasts from 2000 to 0400 and during this time the body is most efficient at the later stages of the digestion process: the absorption of nutrients from the intestines and delivery to the cells. The elimination cycle lasts from 0400 to noon and is the time when the body is most efficient at removing from circulation the byproducts of the metabolic process. Eating during the assimilation or elimination cycles is not recommended, as the body is not prepared to devote its energy to digestion at that time, and if one forces one's body to divert energy from the intestines, liver and kidneys, and/or other parts of the body to the stomach, all processes are performed less efficiently and this can result in health problems, weight gain, restless sleep, etc. The exception is fruit, which can be consumed at any time because it doesn't take a great deal of energy to digest. (Water is another exception of course.) I may have described it a bit too simplistically and yet in rather too much detail, but what I want to know is, is any of this true? —Preceding unsigned comment added by 71.104.119.240 (talk) 21:42, 4 May 2010 (UTC)

The body will adjust to whatever food cycle it is given. If you always eat, exercise or do other events at the same time of day, that's what the body will expect. There is no fixed cycle. Ariel. (talk) 00:54, 5 May 2010 (UTC)

Humans eating pet food

Is it possible to eat cat and/or dog food? What about other kinds of pet food? ScienceApe (talk) 22:25, 4 May 2010 (UTC)

Humans are potentially omnivores although vegetarians object. Cuddlyable3 (talk) 22:32, 4 May 2010 (UTC)

Chap I knew at college ate a tin of dog food for a bet once. Mind you, he also used to drink gin by the half-pint, so it is possible his judgement was somewhat impaired. DuncanHill (talk) 22:34, 4 May 2010 (UTC)

(ec)Generally, yes. We might not like them very much, having less taste for innards than dogs or cats do, but we could probably subsist on them reasonably well. It's possible to eat birdseed or fish food (it's possible to eat dirt, too) but it would be hard to derive much nutrition from them. Note, though, that dogs and cats make their own Vitamin C and we don't. There may be other such differences. So if you want to live on them, you might need some supplements. PhGustaf (talk) 22:40, 4 May 2010 (UTC)

Although pet food bags are generally labeled "Not For Human Consumption," there's nothing in cat or dog food that's really going to hurt the average person. Pranksters, mischievous older siblings, and pet-loving parents can all tell you stories of humans who ate dry pet food once or twice and lived to tell the story. It's also been reported in the past that some elderly or disabled individuals, struggling to get by on their government handouts, would eat canned wet dog food because it was cheaper than meat considered fit for human consumption. I would guess that dog food would be more nutritious for a human than cat food, because humans, like dogs, are omnivores (yes, even the vegetarians; being an omnivore is a fact of human biology and refers to what the body is equipped to chew and digest, whereas vegetarianism is a lifestyle choice), whereas cats are carnivores. Some columnist, I forget who, once said that if you could only eat one food for the rest of your life, dog food wouldn't be a bad choice - it's specially formulated to meet the complete nutritional needs of an omnivorous mammal. 71.104.119.240 (talk) 00:46, 5 May 2010 (UTC)

The reason they say "Not For Human Consumption" is because the factories that make it don't follow the same food hygiene/food safety procedures as are required by law for food intended for human consumption. That means there is a slightly increased risk of food poisoning compared to eating human food, but that's about it (and given that dogs aren't always getting food poisoning, I think we can assume the risk is still minimal - it's probably just the paperwork they don't bother with rather than the actual hygiene). --Tango (talk) 01:08, 5 May 2010 (UTC)

I've been told that the average dog or cat has a "hardier system" than the average human, which is why they can eat things that aren't labeled for human consumption. Whether or not this is true I can't say. You'd have to have a pretty hardy stomach to handle some of the things I've known dogs to gulp down their greedy gullets, but I don't know it would affect the average human to eat insects, burrs, and day-old things, so it's hard to say for sure whether dogs have some kind of systemic advantage. Humans are fussier than they used to be, so it's possible we can't handle some of what our pets consume, and our ancestors consumed, on a regular basis. 71.104.119.240 (talk) 01:15, 5 May 2010 (UTC)

It would be remiss not to mention Ann Hodgman. Her article on the subject is pretty funny. (Note that there are a lot of things that don't kill people but carry some kind of risk of long-term effects. I doubt that anyone has any interest in doing studies on the subject.) Paul (Stansifer) 02:04, 5 May 2010 (UTC)

Record Maximum

http://climate.weatheroffice.gc.ca/climate_normals/results_e.html?Province=NU%20%20&StationName=&SearchType=&LocateBy=Province&Proximity=25&ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=&LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes=&NormalsClass=A&SelNormals=&StnId=1774&

How can the record max for Pond Inlet, NU, be 25.7C recorded in March when the temp has never reached that even in July? —Preceding unsigned comment added by 78.32.155.164 (talk) 23:50, 4 May 2010 (UTC)

Options include a) the weather event on 5 March 1993 was a freak b) the data is wrong c) you're imposing expectations on the data which are not entirely supported by the data. We had 22 degrees in July, but 21.5 in February. How much of a problem is 25.7 in March, given the February value? Sure, it's counter-intuitive, but non the worse for that. --Tagishsimon (talk) 00:01, 5 May 2010 (UTC)

Surely you've answered your own question? Nil Einne (talk) 00:10, 5 May 2010 (UTC)

May 5

Fucking Magnets!

HOW DO THEY WORK?

Are you asking how magnets fuck? Or are you just interested in magnetism? 71.104.119.240 (talk) 00:27, 5 May 2010 (UTC)

Both. —Preceding unsigned comment added by 69.180.172.142 (talk) 00:37, 5 May 2010 (UTC)

It has to do with all the electrons in the magnet being aligned a certain way so the subatomic forces don't cancel each other out. Why it is that the subatomic forces exist in the first place, I can't say. 71.104.119.240 (talk) 00:53, 5 May 2010 (UTC)

They exist because if they didn't we wouldn't be here to notice it. (See anthropic principle - it's the best answer to "why" questions we have. Science is good at "how" but it doesn't really do "why".) --Tango (talk) 01:09, 5 May 2010 (UTC)

Sure you're not just interested in ICP lameness? DMacks (talk) 01:22, 5 May 2010 (UTC)

For those not in on the joke, see Miracles (Insane Clown Posse song). Incidentally the New York Times had an amusing article on this meme. Regarding magnets:

VIOLENT J: I think we might have misused the word miracle. These things we mentioned in the song, they can all be explained. But what we’re doing is appreciating them. Even the infamous line “Magnets, how do they work?” I mean, yeah, we know how magnets work. But they’re still incredible. You can push something across the table without touching it.''

SHAGGY 2 DOPE: Come on, man. The North and South Pole makes a rock magnetic, and if you touch a piece of metal with it, that becomes magnetic? That’s crazy.''

I kind of agree, to be honest. I find magnetism pretty magical, scientific explanation be damned! --Mr.98 (talk) 01:54, 5 May 2010 (UTC)

Gulf war oil spill

Is the claim that 36 billion gallons of oil was released in the Gulf War oil spill as ridiculous as it sounds to me? I'm ready to remove the quotation, reliable sources be damned, considering how silly it sounds. Thoughts? Magog the Ogre (talk) 01:04, 5 May 2010 (UTC)

As our article says, it is orders of magnitude bigger than all the other estimates we have. My guess is that the Times article is getting confused between the Gulf War oil spill and the Kuwaiti oil fires. The latter may well have burnt 36 billion gallons of oil, but I don't think that much has ever been spilt at sea. --Tango (talk) 01:15, 5 May 2010 (UTC)

For the record, it takes the entire US a month a half to consume that much oil. Magog the Ogre (talk) 01:22, 5 May 2010 (UTC)

Medical question

What is the name of the disease when the body has trouble keeping fat and storing it, and the sufferer is underweight as a result? I saw it describled on a medical TV show, but I didn't quite pick up the name. ```` —Preceding unsigned comment added by 76.229.150.6 (talk) 01:34, 5 May 2010 (UTC)

Silver mineral

How does this type of silver form? 149.169.218.250 (talk) 01:49, 5 May 2010 (UTC)

By precipitation from hot sulfurous solution (such as in geysers, fumaroles, those kinds of places) due to the action of the dissolved hydrogen sulfide (generally upon cooling of the solution -- the stuff is slightly soluble in hot water, but completely insoluble in cold water). FWiW 67.170.215.166 (talk) 02:29, 5 May 2010 (UTC)

What is the current state of Computer text to speech compare to human readers?

Two question: is good/modern computer TTS system better reader then "average Joe" who is a human native speaker reading same text aloud? If yes, is computer TTS as good as professional announcer (TV, radio etc.)? 1) Sounds as good as human pro. 2) Very close. 3) Still far away, but better then average Joe.

As to give an example of good TTS, I generated mp3 on my computer from reading few paragraphs of introduction to Bird article. http://www.autohotkey.net/~TePe/BirdsIntro.mp3 TTS I used probably not the best one out there, but still quite good IMHO. And the reason I'm asking, I'm very curious, but ESL here, and computer sounds totally perfect for me. But my judgment could be clouded, plus once again, mine English is far from perfect. PS. Lets not go into acting and emotion, sure computer could mimic them, but there is too much room for good or bad taste opinions etc. Lets stick with reading informational articles like most on Wikipedia etc. 70.48.64.135 (talk) 01:52, 5 May 2010 (UTC)

It still sounds like a computer to me, regarding the tone. It still has something of a Stephen Hawking quality, and the timing of some words is off. Some of the words are a bit wrong to my ear (e.g. the second "i" in "fertilizer" is pronounced wrong), but it's not bad. What throws it off is the pitch at the end of words, and the timing between words, which is not very natural. It is definitely not as good as a professional announcer to a native English speaker. I have definitely heard better text to speech than that, though. --Mr.98 (talk) 02:29, 5 May 2010 (UTC)

I don't think the bird recording comes anywhere near to even an average native speaker in terms of quality. --99.237.234.104 (talk) 02:38, 5 May 2010 (UTC)