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December 14

are imine groups stabilised by base?

My class always seemed to discuss imine in terms of equilibrium (e.g. excess HOH ==> hydrolysis; distillation of HOH and excess amine allows formation of imines), but it seems to me that an imine group would survive in water without being deaminated under basic conditions, whereas hydrolysis would be catalysed by acid. (Ignoring the fact that acid prolly changes the equilibrium by deactivating the amine.)

In neutral solution, assuming equal abundance of HOH and amine, would a C=N bond tend to equilibrate to 50% C=O and 50% C=N? I know the bond energies are different but NH2- is a bad leaving group, NH3 is a decent leaving group (sorta?), whereas HOH is only formed as a leaving group under much rarer conditions and certainly much rarer in base! John Riemann Soong (talk) 00:56, 14 December 2009 (UTC)[reply]

If you know there is a stability difference, it would be silly to assume there is an equal distribution at equilibrium. Thermodynamic equilibrium is the same as the balance of the forward and reverse reaction rates. General equilibrium direction is stated in the very first paragraph of the imine article. DMacks (talk) 14:06, 14 December 2009 (UTC)[reply]

Well yes, but mass action principles often seem to overrule enthalpy considerations. I'm wondering just looking at leaving group principles. John Riemann Soong (talk) 00:49, 15 December 2009 (UTC)[reply]

time/temperature formula

Is there a formula to convert cooking time sufficient to kill pathogens such as cooking chicken for 20 minutes at 170 to the time required to kill all pathogens at a temperature of only 120? 71.100.0.206 (talk) 02:03, 14 December 2009 (UTC) [reply]

Is that degrees Fahrenheit or degrees Celsius? You can't kill all pathogens at all at normal atmospheric pressure (except by burning the food); you need a pressure cooker to do that. Certain temperatures from 140 °F (60 °C) to 180 °F (82 °C), depending on the variety of food, will prevent the growth of bacteria and/or destroy any toxins that might have already been produced by bacteria, over the period of time food is normally held between cooking and serving (no more than 4 hours). Below 140 °F (60 °C) bacteria can grow and the heat can do more harm than good. --Jc3s5h (talk) 02:20, 14 December 2009 (UTC)[reply]

Fahrenheit. I read somewhere that vegetarians cook at 118 deg F so maybe the reason is only flavor? 71.100.0.206 (talk) 02:48, 14 December 2009 (UTC) [reply]

I would not recommend cooking chicken at either 170°F or 120°F. My meat thermometer says that, for poultry to be cooked it should reach a temperature of 190°F, and you're clearly not doing that if you're cooking at a temperature below that. Cooking chicken in an oven would typically be done at 200°C (~400°F) so trying to cook at the very low temperatures you're talking about seems an impossibility. --Phil Holmes (talk) 15:15, 14 December 2009 (UTC)[reply]

The 118°F thing may be a reference to a raw food diet, not an ordinary vegetarian diet, but the number is a little different than what our article says. For cooking meats at a low temperature for a long time, see sous-vide. And I don't want to eat chicken that's been cooked to 190°F. 165°F is plenty. -- Coneslayer (talk) 15:30, 14 December 2009 (UTC)[reply]

200 F sounds way too low, and it would take a very long time for the internal temp to creep up to 190. My old 1981 "Better Homes and Gardens Cookbook" says to roast chickens at 375, under 2 pound chickens at 400, turkey at 375, goose at 350, and foil wrapped turkey at 400. It calls for an internal temperature of 185 in the thigh meat as a doneness test. Edison (talk) 19:54, 14 December 2009 (UTC)[reply]

depurination

Why isn't depurination a much larger problem than it seems to be? I know there's BER, but I mean, a purine glycosidically linked to a sugar seems to be quite problematic, because purine seems to be a good leaving group, and that anomeric carbon is all the more reactive to SN2. John Riemann Soong (talk) 02:50, 14 December 2009 (UTC)[reply]

Also why isn't depyrimidination also a mutation regime? Glycosidic-bonded pyrimidines have a carbonyl at the 2' position, effectively making a 2N-nitrogen an amide (negative charge can be delocalised onto the oxygen) so a pyridine lone pair could be similarly delocalised. John Riemann Soong (talk) 03:09, 14 December 2009 (UTC)[reply]

Scanning for a lost cellphone

Hi, I've lost my cellphone. It might have been stolen (it's now blocked for outgoing calls, just in case) but it's on and I suspect it's in my house. I can call it and I get the "calling" sound in the phone I call from but I can't hear it ringing (if it's in the house, the sound must be off or it's surrounded by pillows or something). It's an iPhone but I think the WLAN is not transmitting when it's not being actively used. Is there any way I can "scan" my house for it using simple equipment, like a small radio? Would it be feasible to call the phone while walking around with a radio to see if I hear interference on the radio? If so, would anything other than a radio (just a small speaker, for example) be more likely to work? I'm of course also looking by conventional methods but I just moved and there's a lot of cardboard boxes it could potentially have fallen into (as well as the possibility that it is indeed not in the house). Thanks! Jørgen (talk) 11:23, 14 December 2009 (UTC)[reply]

It turned up without any scanning. But I still think it was an interesting idea... :-) Jørgen (talk) 19:38, 14 December 2009 (UTC)[reply]

Both wifi and bluetooth have RSSI that indicate roughly how close the transceiver is. If you have set your iPhone to automatically connect with a laptop or something you could maybe do some sort of triangulation, although it won't be very accurate. --antilived^{T | C | G} 23:22, 14 December 2009 (UTC)[reply]

The connection between blonde people and intelligence

I have a question, are blonde people really stupid? I mean, does being blonde affect your intelligence? —Preceding unsigned comment added by RocketMaster (talk • contribs) 13:35, 14 December 2009 (UTC)[reply]

Off course not. It is also not true that the chiken crossed the road to get to the other side. Dauto (talk) 14:40, 14 December 2009 (UTC)[reply]

But it is true that silly people post nonsense in Wikipedia at times. JamesBWatson (talk) 15:39, 14 December 2009 (UTC)[reply]

It's a perfectly reasonable question. Sometimes conventional wisdom is right, sometimes it is wrong. Determining which is the case for a particular piece of wisdom is a job for science, not for assuming it must be nonsense because you've been brought up with the dogma of equality. So, how about we try and actually find some references for the OP? --Tango (talk) 15:57, 14 December 2009 (UTC)[reply]

Indeed: intelligence is a combination of nature and nurture, and part of the nurture is attributable to one's appearance. A number of studies have shown that unattractive children receive poorer treatment from their parents, for example, which could lead to lower educational opportunities. --Sean 16:18, 14 December 2009 (UTC)[reply]

There could also be a case of self fulfilling prophecy. If culture views blonds as dumb, then smart women who do not wish to have such a stereotype may dye their hair a different color, resulting in a higher proportion of "dumb blonds". 65.121.141.34 (talk) 16:24, 14 December 2009 (UTC)[reply]

It is not a reasonable question. There is NO conventional wisdom about blonds being dumber. Just dumb jokes about it. Dauto (talk) 17:40, 14 December 2009 (UTC)[reply]

Perhaps "conventional wisdom" is the wrong term, but there certainly are people that believe blondes have a lower average intelligence. Jokes don't exist in a vacuum. Even if nobody believed it, it would still be a reasonable question. Empirically verifying things that everybody believes to be true is an important part of science. The refusal to even consider that your assumption could be wrong is the defining characteristic of a dogma, and dogma has no place in science. --Tango (talk) 17:54, 14 December 2009 (UTC)[reply]

Are you asserting, Dauto, that you are a master of every single one of the thousands of cultural enclaves that exist in all of the 192 countries in the world and that you are positive that nobody believes this? You're overstating. Please stop; this is the Reference Desk. Tango is correct. Let's find some citations. This link isn't one, but its hypotheses touch on why physical features and intelligence might theoretically be correlated (the claim is that genes set an upper limit for intelligence and that "genetic clustering occurs due to geographical isolation over long periods of time, and continues through inheritance", so you could see how, say, hair color and intelligence might be correlated because one particular group happens to be of a certain hair color and of a certain intelligence range. This is surely controversial but that's something to debunk with a link to a study, not by trying to shout it down). Comet Tuttle (talk) 18:00, 14 December 2009 (UTC)[reply]

We do have a dumb blonde which says "This stereotype (and the associated cognitive bias) may have some negative consequences and it can also damage a blonde person's career prospects. [1]" which I think calls into question the idea it's simply dumb jokes. Conciously the people may say it's a dumb jokes but the study here suggests subconciously at least they are being influenced. I have read of other studies before that have been summarised as "blondes really do have more fun" specifically they've found that people (or women?) who dye their hair blonde start to behave differently and also induce different responses from people IIRC. To put it a different way, as with many stereotypes, whether they have any truth or not, people subconciously at least respond to them. And in fact I agree with Tango here, as with many stereotypes there are certainly people who do conciously believe them to some extent.

And repeating what has been said above, it seems likely to me there will be some influence therefore on the blonde's 'intelligence'. To clarify, I should say I'm not referring to intelligence as defined by some IQ score but more generally in terms of knowledge and other things which make the difference between a 'smart' person and a 'dumb' person. Anyway if other people have lower expectations of that person and therefore the person is not pushed so hard to achieve and is given less opportunities to succeed (the study for example) it seems likely this will often negatively influence their intelligence. And conversely since when the person does have to do something they may have to put in less effort to succeed again that's likely to negatively influence their intelligence. Nil Einne (talk) 19:24, 14 December 2009 (UTC)[reply]

Tango, Equality is not a dogma. You seem to be confusing it with a virtually nonexistent belief that there are no differences between people. Equality is simply not taking one person's observed behavior or intelligence and attributing it to trivial factors such as appearance (i.e. blonde hair) with no non-biased attempt to find any actual evidence of a cause-effect relationship between said blonde hair and the specific behavior or intelligence, thereby wrongly assuming that all people with the same appearance (i.e. blonde hair) are less intelligent then non-blondes. --Itwilltakeoff (talk) 00:17, 15 December 2009 (UTC)[reply]

Equality is dogmatic for some people (like Dauto). Of course it isn't for everyone, for plenty of people it is just an assumption based on evidence, or lack thereof. The difference is whether or not you are willing to consider that it might be wrong. --Tango (talk) 00:53, 15 December 2009 (UTC)[reply]

Also, the Stereotype threat article may interest the OP.

Which leads to the vastly more interesting question of whether or not blondes have more fun. ~ Amory (u • t • c) 01:38, 15 December 2009 (UTC)[reply]

I mentioned the study earlier. I found some mention of it here [2] [3]. I couldn't find if it was published or where, one of the articles links to a press release which doesn't work, I didn't try that hard. Some obvious flaws occured to me when reading this study and when writing about it above which I didn't bother mention but found this which does a resonably job of highlighting them [4]. The second ref and [5] mentions some other studies with more ambigious results and [6] [7] suggests blondes may have more fun, unless they want to get married/settle down. It's apparently also a question which interested Darwin [8] [9] so I guess you're in good company for wanting to know. I also noticed this mostly unrelated thing about improvements in modelling blonde hair and the reasons it's difficult [10] which perhaps SB can help clarify if anyone is interested. Nil Einne (talk) 10:10, 15 December 2009 (UTC)[reply]

"It takes a smart woman to play a dumb blonde." (I don't remember who said that, but check out my search results in this Wikiquote search results).Civic Cat (talk) 20:10, 17 December 2009 (UTC)[reply]

What medicine stops the itchiness inside of nose?

This question appears to be a request for medical advice. It is against our guidelines to provide medical advice. You might like to clarify your question. Thank you.

Responses containing prescriptive information or medical advice should be removed and an explanatory note posted on the discussion page. If you feel a response has been removed in error, please discuss it before restoring it.

-- Scray (talk) 03:05, 15 December 2009 (UTC)[reply]

Irritation

Why does a body part become red when its irritated?Accdude92 (talk to me!) (sign) 14:43, 14 December 2009 (UTC)[reply]

I believe it is a histamine response. The redness is due to increased blood flow to the area. --Tango (talk) 15:06, 14 December 2009 (UTC)[reply]

Yes -- check out rubor. DRosenbach ^{(Talk | Contribs)} 03:10, 15 December 2009 (UTC)[reply]

Faroe Islands tunnels/civil engineering.

What are the main civil engineering companies, or company, in the faroe islands? I mean for instance who builds the most tunnels? —Preceding unsigned comment added by 188.74.72.115 (talk) 16:04, 14 December 2009 (UTC)[reply]

We have a List of tunnels of the Faroe Islands - there aren't that many of them. 75.41.110.200 (talk) 21:57, 14 December 2009 (UTC)[reply]

See the Miscellaneous section. By the way that's a real lot of tunnels for only 49,000 people to use. The Danish taxpayers have spent more than a billion Euros on them and now they want independance[11]. Alansplodge (talk) 23:25, 14 December 2009 (UTC)[reply]

Following a link in the Norðoyatunnilin article (the only one linked in the "list of" page), I find this page: http://www.tunnil.fo/Default.asp?sida=565 . From what I can read from it (Norwegian and Faroese separated some 700 to 1000 years ago, so not much) it seems NCC constructed that tunnel. In general I would expect most or all tunnels on the Faroes to have been constructed by foreign companies. Jørgen (talk) 07:33, 15 December 2009 (UTC)[reply]

Google also gave me this (only part of an article, but one more (or the same) example of NCC building a tunnel there) Jørgen (talk) 07:36, 15 December 2009 (UTC)[reply]

Tail on Human

Could this be true that some humans were born with a tail? This is video of a woman showing her tail note: it is a porn video. with a tail. —Preceding unsigned comment added by 74.14.119.246 (talk) 16:24, 14 December 2009 (UTC)[reply]

Well, who knows about the video—one should never look for reality in porn. But our article on Tail covers the possibility of human tails quite well, check it out. --Mr.98 (talk) 16:28, 14 December 2009 (UTC)[reply]

To put 98's comment in a different way, humans can have tails, but while I haven't looked at the video it's quite doubtful IMHO that the woman in the video really has a tail Nil Einne (talk) 19:21, 14 December 2009 (UTC)[reply]

I watched it and it was obviously fake. --Sean 22:12, 14 December 2009 (UTC)[reply]

Quite so. Martin Hogbin (talk) 11:13, 19 December 2009 (UTC)[reply]

Both my nephews were born with tails - instead of curving inwards, the coccyx curves outwards. --TammyMoet (talk) 18:42, 14 December 2009 (UTC)[reply]

See also our Atavism article. 87.81.230.195 (talk) 21:17, 14 December 2009 (UTC)[reply]

And Human tails and this [12] and [13] Alansplodge (talk) 23:19, 14 December 2009 (UTC)[reply]

Theories vs. laws (Re: Einstein)

Hi. I've been trying to figure why Einstein's theories of Relativity are still widely considered theories and not laws, and how there aren't even aspects of those theories that are considered laws per se. I know there have been discussions about the subject here already. What I want to know is if what I found at the Physical laws article is true (and would therefore explain calling Relativity a theory and not a law):

Physical laws are distinguished from scientific theories by their simplicity. Scientific theories are generally more complex than laws; they have many component parts, and are more likely to be changed as the body of available experimental data and analysis develops. This is because a physical law is a summary observation of strictly empirical matters, whereas a theory is a model that accounts for the observation, explains it, relates it to other observations, and makes testable predictions based upon it. Simply stated, while a law notes that something happens, a theory explains why and how something happens.

So, is this really true? Even if it is, I could argue that certain formulas or concepts within the theories of relativity could be isolated and named "laws", right? PS. I found it very curious to know that Relativity is the only item in the List of laws in science article that is still a theory... 190.157.136.97 (talk) 16:42, 14 December 2009 (UTC)[reply]

This issue has been discussed many times on the RD before. You may want to read those discussions first and then come back with anything that still confuses you Nil Einne (talk) 16:59, 14 December 2009 (UTC)[reply]

Yes, that definition is correct. "Still a theory" is nonsense - a theory is a good as it gets. "Theory" in science doesn't mean "something that hasn't been proven", as it does in everyday usage, since there is no concept of proof in science. Something like "E=mc²" could be described as a law, I suppose, as could "the speed of light is constant". They are simple statements that have been empirically demonstrated. The idea that theories become laws is just not how science works and is generally nonsense spread by creationists trying to discredit the theory of evolution. --Tango (talk) 17:02, 14 December 2009 (UTC)[reply]

For example, the Lorentz transform is a law which governs the composition of velocities in the theory of special relativity. However, this law only describes a small portion of the total class of phenomena which might be explained in a special relativitistic treatment. Compare, for example, how Ohm's law is the simplified governing equation for a more general theory of electrical conductivity and an even more general quantum theory of conductivity. Not only is the theory more complex, but it includes the law(s) as special-case simplifications of the general physics. Furthermore, different theories can support some of the same law(s), as is the case when a simpler theory is a proper subset of more generalized theory. Nimur (talk) 17:50, 14 December 2009 (UTC)[reply]

E=mc² is a law: it is a description of mass-energy equivalence. I suppose we could name it something like "the law of mass-energy equivalence". There are two different theories of relativity "special relativity" and "general relativity". --Jayron32 18:56, 14 December 2009 (UTC)[reply]

Don't forget Galilean relativity. Einstein wasn't the first to theorise about things being relative. --Tango (talk) 18:59, 14 December 2009 (UTC)[reply]

This is a very good article comparing evolution with gravity: Evolution as theory and fact. --Mark PEA (talk) 19:35, 14 December 2009 (UTC)[reply]

Actually, that article is not even a Good Article, much less a "very good article". Comet Tuttle (talk) 19:42, 14 December 2009 (UTC)[reply]

No, no, no! Nonsense. An article can be extremely good in every regard - but if nobody offers it to the WP:GA crew to check out, it'll never become a Wikipedia:Good article. SteveBaker (talk) 01:34, 15 December 2009 (UTC)[reply]

A law is just a theory with a good PR agency.Sjö (talk) 21:06, 15 December 2009 (UTC)[reply]

Yes, in physics at least there is no distinction between laws and verified theories. One problem is that the word 'theory' also includes more speculative theories such as string theory. Unfortunately there is no official system in science to declare theories laws when they are accepted. Martin Hogbin (talk) 11:19, 19 December 2009 (UTC)[reply]

foggy car windows

What atmospehric conditions must there be for a car's window to fog up?Accdude92 (talk to me!) (sign) 20:19, 14 December 2009 (UTC)[reply]

The basic cause is that the glass is colder than the air on one side of the glass. Based on the humidity of the air, there is a dew point (a certain temperature) below which the water evaporated in the air will condense into liquid. If the window is colder than the dew point of the air, water will condense on the glass in very small droplets, which is what makes it foggy. —Akrabbim^talk 20:27, 14 December 2009 (UTC)[reply]

Further to this subject, is there a good, cheap way to minimise the condensation that forms on the inside of a car's windows when it's parked outside during an overcast British winter? My car lacks air conditioning and the windscreen's air blowers (using engine heat to warm cold but humid exterior air) take a considerable time to clear it, as does the rear window's heating element. I have latterly resorted to driving with the side windows half-open for 10 minutes, which works but is no fun in the cold and impractical when it's raining. 87.81.230.195 (talk) 21:12, 14 December 2009 (UTC)[reply]

Clean windows fog up much less than dirty ones. I proved this to a coworker who refused to believe it because it meant that he had to do a minor amount of physical labor. I cleaned the passenger side of the windshield. Then, the next week, I saw him driving down the road leaning over so he could look out the passenger side of the car while the driver side was all fogged up. -- kainaw ™ 21:15, 14 December 2009 (UTC)[reply]

In order to fog up, the window needs Nucleation sites. Basically, in order to change phase from a gas to a liquid, the water molecules need some rough areas to "stick" to first. That's why dirty windows fog up so fast, the particles of dirt provide lots of good nucleation sites. If cleaning the window really well does not work, there are anti-fog coatings and sprays that you can buy at any auto supply store, or the automotive department at your local supermegamart. These are usually surfactants (i.e. soap) that prevents the water from forming tiny droplets. Window fog is essentially lots of little droplets, so by lowering the surface tension of the water, the water forms a thin sheet instead of droplets, and a sheet of water is much easier to see through than lots of droplets are. --Jayron32 21:29, 14 December 2009 (UTC)[reply]

As I remember from my (mispent) youth, a cut potato rubbed over the window helps - also it's not bad if your wiper dies and you want to drive in the rain (Mr. Plod might not approve). Way back in the 60-70's there was a product for the rear window called (I think) GnoMist - a thin sheet of plastic which clung to the screen (like some of those window stickers that aren't sticky), that helped to keep the back window clear, I assume the water did not like forming droplets on the surface. Make a mental note for your next car to get one with a heated front window - my Mondeo is just great in keeping the windows clear. Ronhjones ^(Talk) 21:49, 14 December 2009 (UTC)[reply]

I've never heard of GnoMist, but Rain-X and Aquapel are water repellent products available in the US which are supposed to reduce the amount of fogging on windshields. -- 128.104.112.87 (talk) 00:17, 15 December 2009 (UTC)[reply]

Thanks for the suggestions. I admit I'm not big on car cleaning, but I'll give the insides of the windows a go before my next trip. The outsides of the windscreen and back window are no problem. I think the main inside problem is that in our dank British winters, the car's interior never has a chance to dry out properly. Re getting a Mondeo next time, I prefer for various other reasons to stick with the Corsa (I'm on my third, having had Models A, B and C in succession), and in my now-unemployed state see little prospect of changing or replacing my current one for the forseeable future - I can barely afford to keep it on the road as it is! 87.81.230.195 (talk) 15:20, 15 December 2009 (UTC)[reply]

between large vision acuity

This is possible to say 20/100-1 or 20/200+1? What what does this mean? Is 20/100-1 mean like 20/120 and 20/200+1 mean like 20/170 or so? Doctors can do like 20/x+3 if vision is between 20/200 and 20/300, this do happen.--209.129.85.4 (talk) 22:02, 14 December 2009 (UTC)[reply]

I've never seen visual acuity quoted like that. Where did you see it? --Tango (talk) 22:25, 14 December 2009 (UTC)[reply]

Last doctor's visit one eye is 20/100-1 that's what the doctor wrote.--209.129.85.4 (talk) 22:29, 14 December 2009 (UTC)[reply]

Any changes the one is actually a lower-case L? Jc3s5h (talk) 22:36, 14 December 2009 (UTC)[reply]

For "Left eye"? Opticians usually use "S" (from the Latin for left) rather than "L", but I suppose it is possible. --Tango (talk) 00:49, 15 December 2009 (UTC)[reply]

It could be possible that the numbers are actually separate things. The first number (ex. 20/20 or 20/100) might represent the visual acuity expression, and the other number (ex. -1 or 0.5) might represent the number of diopters that the optometrist has prescribed for corrective lenses. 152.16.15.144 (talk) 00:48, 15 December 2009 (UTC)[reply]

December 15

Why isn't t-butyl (as a carboxylate protecting group) sensitive to base?

It seems to me you could perform an E2 elimination and kick out carboxylate as a decent leaving group .... John Riemann Soong (talk) 00:24, 15 December 2009 (UTC)[reply]

The point of using a t-butyl protecting group is that the t-butyl structure represents an extremely bulky group, so effectively the bulk of this group shields the central carbon atom from attack by a base, therefore any elimination requires significantly higher energy than other smaller groups. Rjwilmsi 23:06, 15 December 2009 (UTC)[reply]

That sounds like a conflation of SN2 and E2 modes of reaction. To answer the original question, I ponder "carboxylate as a decent leaving group"^{[citation needed]}. They are easily ejectable if you can generate a β anion directly (2-haloethyl esters under reducing conditions), but I don't know if carboxyl is able to activate β H for direct deprotonation effectively (E2). Are ethyl esters noticeably less stable to non-nucleophilic bases (compare steric shielding of the β H)? DMacks (talk) 23:14, 15 December 2009 (UTC)[reply]

Boiling water simply by adding kinetic energy?

Is it possible in principle to bring water from room temperature to a boil simply by adding kinetic energy via something like an egg beater? If yes, is it possible given the tools available in the average home, or would you need some serious manufacturing/industrial class hardware? Just curious as I gently stir my morning coffee... 218.25.32.210 (talk) 00:40, 15 December 2009 (UTC)[reply]

In theory yes, but it'd be very impractical. A major problem is heat dissipation. (At some point the water will lose more heat than you are adding to it.) And efficiency. An egg-beater is way too weak ... a major problem is that you'll just end up heating the room air instead. If you completely insulated the boiling apparatus in question, and ensured very little heat flow between the container and the outside environment, and dropped in an agitator, you could prolly theoretically boil it. The heat capacity of water (or any solvent for that matter -- even hexane) is kinda large though. John Riemann Soong (talk) 00:46, 15 December 2009 (UTC)[reply]

Given the right circumstances - certainly. If you take an electric drill with a really blunt wood-bit - and try to drill your way into a small chunk of stainless steel - after a couple of minutes of fruitless drilling, squirt a small amount of water into the area and it'll boil immediately. Now, admittedly - we took the kinetic energy of the drill - and used friction to convert that to heat - but the intermediate step is merely a convenience. The question is really whether you can figure out a way to get from motion to convert directly into heat in the liquid. In principle, it's certainly possible - and with a sensitive enough thermometer you'd certainly be able to measure a small, slow heat increase from a fast electric mixing machine or such like. But as John said - the problem is to get the heat into the liquid faster than it'll lose heat to the environment. So you need to agitate the water as fast as possible to get the heat in faster than it's losing it. You'd want an insulated container...that kind of thing. It's got to be possible though - it's just a matter of figuring out a way to do the experiment. SteveBaker (talk) 01:31, 15 December 2009 (UTC)[reply]

My favourite candidate so far is to use a magnetic stirbar. No moving parts, and you could theoretically seal up the container with lots of insulation, then just apply a changing magnetic field! =D Better yet, drop fine magnetic powder and turn on the field. The big thing you see is surface area. If you do some simple calculations, you find your agitator is adding very little energy (most of the energy doesn't end up in the water, even without the water losing anything). Very fine particles being moved about means more surface area ===> more friction ===> greater heating efficiency. John Riemann Soong (talk) 01:36, 15 December 2009 (UTC)[reply]

Nod, keep in mind that 'heat energy' is for all intents and purposes just kinetic energy on a small scale, IE the energetic movements of atoms unless I was deceived as a child. Unomi (talk) 01:44, 15 December 2009 (UTC)[reply]

An interesting extension is to use something with an electric dipole or that is ionic...apply an oscillating electric field and the molecules vibrate and collide with each other to heat the material. 173.79.45.179 (talk) 05:17, 15 December 2009 (UTC)[reply]

Related: frictional heating from the mixing is an important factor when kneading bread dough mechanically. --Sean —Preceding unsigned comment added by 76.182.94.172 (talk) 01:34, 15 December 2009 (UTC)[reply]

I've been told that a step in the commissioning of a nuclear power plant is to generate steam and produce a few megawatts of power from the turbogenerator without any nuclear power input, simply by running the boiler feed pumps to recirculate the water in the boiler. James Prescott Joule investigated the mechanical equivalent of heat in the mid 1800's. He used a falling weight to spin a paddle in an insulated container of water, and noted how much mechanical work it took to raise a given mass of water by a given temperature.His result was 772.24 foot pound force (4.1550 J·cal-1). He found that 772.24 foot-pounds of work raised one pound of water 1 degree F. His claims were rejected by many scientists, who still like "caloric" theories and did not generally accept conservation of energy as part of their core scientific beliefs, but eventually gained acceptance. See also Mechanical equivalent of heat. I leave as an exercise for the reader how much work one would have to do to raise say 1 liter of water from 20 c to 100 c by manually spinning the paddles, or cranking an eggbeater in an insulated bit of water. If a healthy person can produce 1/4 horsepower for over an hour, where a horsepower is 746 watts or 33000 pound-feet per minute how long would it take at 100% efficiency in the mechanical apparatus and perfect insulation of the water container to get a liter of water boiling? (Today we know that the question basically "boils down" to Joules per second of energy input and the specific heat of water.) Edison (talk) 15:37, 15 December 2009 (UTC)[reply]

Actually this is one case I think where the apparatus would not need to be 100% efficient, since losses in efficiency are caused by things like friction, which would generate that heat anyways. 65.121.141.34 (talk) 16:35, 15 December 2009 (UTC)[reply]

I was assuming no friction outside the insulated water vessel, like in a treadmill linkage , or pulleys to speed up the rotation, or a gear box, and all. Note that .25 horsepower as the human input is also a crude number, so it could be .1 hp or .5 hp for a few minutes, and depends on the fitness of the individual. So would it take seconds, minutes, hours, or days for a hard working person to boil 1 insulated liter of water by mechanical agitation? Edison (talk) 00:40, 16 December 2009 (UTC)[reply]

So with the above caveats, and Joule's figures of 772.24 foot-poundforce of work required to raise one pound of water 1 degree F, an assumed 1/4 horsepower of human effort (8250 foot-poundforce per minute), starting at 70 deg F, neglecting changes in specific heat of water, 2.2 pounds of water per kg, I get 29.2 minutes of hard work to raise it to 212 °F (100 °C). At a more relaxed 1/10 horsepower (74.6 watts human effort), it would take 73.1 minutes. This only raises the water to the boiling point, but does not boil it away. It is interesting that in 1842, when Joule presented his findings, conservation of energy was in doubt among scientists. It took Joule and Helmholtz to lay the groundwork for modern physics, chemistry and engineering in this area. Joule's work was initially denied publication because they saw him as a non-scientist, and they doubted he could accurately measure very small temperature changes. Edison (talk) 20:12, 16 December 2009 (UTC)[reply]

Car windows again

The above question from yesterday reminds me of a related question that I have long puzzled over. Several people have assured me that setting the blowers to cold will clear condensation from the inside of a windscreen quicker than if they were set to warm. This does seem to be true, even though it goes against what I would intuit: shouldn't warm air perform this function more efficiently?--Shantavira|^{feed me} 08:25, 15 December 2009 (UTC)[reply]

The condensation is there because the car is warm inside while it's cold outside. So why do warm blowers work at all? 213.122.69.70 (talk) 08:50, 15 December 2009 (UTC)[reply]

Did you even bother to read the answers from yesterday? Warm blowers work because the problem is cold windows in wet air. If you warm up the windows (by blowing warm air on them), the condensation will get slower and slower until it stops, and in addition, the warm air will evaporate the drops that are already there, because warm air can "store" more water vapor than cold air (and the flow of air helps, too). --TheMaster17 (talk) 09:19, 15 December 2009 (UTC)[reply]

I read the sentence about the dew point, yes, but I didn't know car blowers preferentially heat the windows. The ones I'm familiar with are pointed towards the middle of the car. I didn't know that warm air can store more water vapour than cold air, either - does that reduce the effective humidity, meaning the dew point gets lower? I guess that's the critical piece of information. 81.131.54.224 (talk) 15:24, 16 December 2009 (UTC)[reply]

You may be misunderstanding the advice... if you turn on the air conditioning, it will dry the air and improve evaporation. But even with the air conditioning on, you should have the heater set to warm, so the air that blows is warm and dry. -- Coneslayer (talk) 12:31, 15 December 2009 (UTC)[reply]

There are two effects going on here. The amount of water that the air can hold depends on temperature. Warm air can hold lots of water - cold air, much less. So - when your car is cold, the water in the warm air in your breath hits the cold windshield and cools rapidly. At that point, the water can't stay in the air so it forms as droplets on the windshield. Hence:

The A/C cools the air - but also dries it (it's not an "air refrigerator" - it's an "air conditioner" - it "conditions" the air - removing dust and moisture as well as cooling it down). Drying the air reduces the water content (irrespective of temperature) and without water in the air, there is nothing to condense.
The heater warms up all of the air in the car - but since that air was formerly cold - it didn't have much water in it. So now the car is warm (and dry) and your breath can dissipate water into all of the other warm air in the car which (being dry) is easily able to hold it. Also, the warm air heats up the windshield so that when warm, moist air does touch it, it's not cooling the air down enough to allow the water to condense.

Hence either heating or cooling the car will eliminate mist from the glass. In fact, because the main source of all of this water is your body - simply turning on the fan and replacing the air inside the car with outside air will remove much of the moisture and prevent misting. Just blowing the air onto the windshield will maintain a barrier of drier air and thereby prevent your moist breath from getting in contact with it.

Hence, almost anything you do with the car's heating/cooling controls will help to demist it. However, the airconditioner (on cold) works best because it's literally removing the water - not just moving it around. SteveBaker (talk) 14:44, 15 December 2009 (UTC)[reply]

". . . The main source of all of this water is your body . . . ." Steve, you've been living in Texas for too long :-)! Back here in waterlogged Ukland, the environmental humidity (combined with lack of sunlight) is the principal problem - my internal fogging accumulates during the days I haven't driven, not when I'm in the car and driving - and hence delays my starting out. 87.81.230.195 (talk) 15:30, 15 December 2009 (UTC)[reply]

I disagree - on a cold day, there simply isn't "room" in the air for much water. Even at 100% humidity, there isn't much water in cold air. But the air from your lungs has been warmed and moisturized...so it does add the majority of the water. Your car may fog up when it's warmer inside the car than out - but there has to be some other source of water...perhaps you have a water leak accumulating water in the upholstery or carpet. If so - you need to fix it before you get mold growing in there - it's virtually impossible to erase the stink of mold in a car. SteveBaker (talk) 18:14, 15 December 2009 (UTC)[reply]

Fair point. I'll look for a leak as far as I'm able. 87.81.230.195 (talk) 10:34, 16 December 2009 (UTC)[reply]

Shatika

Resolved

Where can I find more information on Shatika? Regards-Shahab (talk) 09:07, 15 December 2009 (UTC)[reply]

Irrelevant discussion because OP mis-spelled sciatica

My guess would be that the snake oil article would be a good place to start. Keep in mind that these sorts of products are rarely regulated, so their claims of efficacy may be totally fictional. Nimur (talk) 13:16, 15 December 2009 (UTC)[reply]

Don't be too hard here. The product is Ayurvedic rather than allopathic. Sometimes I think we're guilty of judging one culture by another culture's lights. I know that's heresy on a science reference desk, but what the hey. --TammyMoet (talk) 13:51, 15 December 2009 (UTC)[reply]

Oh - yes, we can be that hard! This is the science desk and we don't stick our heads in the sand and say things are OK just because it comes from another culture and therefore we must respect it somehow. That is 100% not how science works - we judge things by the facts - and culture simply doesn't enter into the equation. What you just said is beyond heresy - it's completely f**king stupid.

So - let's do this properly. Let's examine the claims made for the stuff: It says that it "Relieves pain" - OK - maybe. Much of pain is psychosomatic and any placebo can do that. So - yeah - maybe.

But it also says that it cures: Arthritis(Osteoarthritis,rhumetoid arthritis),Spondylitis and Migraine. Pick any one of those: Osteoarthritis let's say. This is a disease that's caused by physical wearing and degradation of cartilage around the joints. Unless this oil somehow causes a magical regeneration of cartilage (something completely unknown in humans) - then it can't "cure" osteoarthritis - at best it might relieve the pain - but they already said it relieves pain in general, so they must be talking about something more specific. We don't say "Tylanol cures Osteoarthritis" - although it does help the pain. Spondylitis isn't even a specific disease - it's a symptom of many possible diseases...curing it would require fixing all sorts of odd problems - none of which seem to be listed?!? Curing migrane would require getting involved with seratonin inhibitors in the brain...this would have to be a substance capable of crossing the blood-brain barrier. Such a substance should be regarded with EXTREME caution! In short - if this stuff did what it said - it would be capable of doing untold amounts of harm too! If you used it to cure your Arthritis and it started leaching into your brain and messing with your seratonin levels - the consequences would be horrific!

Where is the list of side-effects. No change that you do to the body comes without changes elsewhere. If it's curing one thing (say your migrane) then whatever effect it has on stimulating the growth of new cartilage in osteoarthritis would cause who-knows-what joint changes in people who have no cartilage problems to start with!

If this stuff works as advertised - it's lethally dangerous and I wouldn't want to be within 50 feet of an opened bottle! If it doesn't work (as I STRONGLY suspect) - then don't buy it because it's snake-oil.

At best, this is a mild pain reliever - probably more for psychosomatic reasons than anything else. My mother uses 'witch hazel' to relieve her migranes - it's very clear that it's not doing anything but acting as a credible placebo for her - so I'm not going to tell her that it's useless. This stuff is likely doing the same thing.

Sorry - but science CAN discuss these kinds of matter.

SteveBaker (talk) 14:27, 15 December 2009 (UTC)[reply]

Out of curiosity several Shell lubricants contain salicylates (Alexia has the most check Google) and we did sometimes come across people abroad massaging it into arthritic joints apparently with some benefit (obviously, this is not medically safe, but aspirin is a salicylate of course). Conventional analgesics can be absorbed by the skin, and do occur in tree bark etc but as I think Steve's said before the ones which work are sold as medicine and the ones which don't work are snake oil. --BozMo talk 14:46, 15 December 2009 (UTC)[reply]

...and this stuff might (maybe) work as a pain reliever. But that's not all that it claims. It's actually claiming to CURE a wide variety of incurable conditions. If you want a topical salicylic acid (asperin) cream then buy something like 'Aspercreme' - which does contains exactly what you need and is unlikely to add a bunch of other things that you don't need. SteveBaker (talk) 15:22, 15 December 2009 (UTC)[reply]

Just out of curiosity, Steve, do you call your mother really fucking stupid for using the witch hazel? You're a smart guy and I appreciate your knowledge, but that was really fucking rude. Matt Deres (talk) 15:11, 15 December 2009 (UTC)[reply]

As a side note, I do call my mother "fucking stupid" when she fails to read the scientific papers I download for her questioning the efficacy of the various CAM products she likes to buy. I tend to get many thought terminating clichés in return for it, but some people just can't be taught it seems, even the organism from which I'm derived. --Mark PEA (talk) 18:03, 15 December 2009 (UTC)[reply]

No - I don't - but then she doesn't wait for a question about the efficacy of a dubious commercial product on a science reference desk and then tell us we can't answer the question because it's culturally sensitive (and the two asterisks don't stand for 'u' and 'c' - that would be rude). SteveBaker (talk) 15:17, 15 December 2009 (UTC)[reply]

omg!! I've been insulted by the great SteveBaker! That's really made my Christmas! By the way, my rheumatologist told me to take glucosamine for my joints. I always assumed if a qualified medical doctor told me to take a tablet then it would work. Is that not the case now? The original question, by the way, wasn't about the "efficacy" of a product, it was "where can I find more information on", and in that case the correct response should not have been to refer to "snake oil", but to the product website. I guess I'm as guilty as the responder as assuming cultural norms here. --TammyMoet (talk) 16:10, 15 December 2009 (UTC)[reply]

Firstly - I'm fairly sure your rheumatologist didn't say that glucosamine would "cure" your arthritis (certainly not osteoarthritis). Secondly - read our article on Glucosamine...pay special attention to the bits about the results of clinical trials. SteveBaker (talk) 17:22, 15 December 2009 (UTC)[reply]

We mis-understood the question the OP was asking, and devolved into a tangential discussion. Nimur (talk) 21:36, 16 December 2009 (UTC)[reply]

All of you have misunderstood my question. I want information on shatika, which is a problem with the nerves. I do not want information on the herbal remedies etc-Shahab (talk) 16:38, 15 December 2009 (UTC)[reply]

Well, the trouble is, there is no such English language word as "Shatika" - so all we could do was to go by the link you posted. That said - I wonder if you mean "Sciatica" (pronounced "sigh-attic-a") - which is a fairly common nerve condition (which that oil won't cure either!). If that is the case - then read our excellent article: Sciatica. Sadly, we're not allowed to give medical advice - so we may not be able to help you much more than that unless your interest is of a more general nature. If you have sciatica (or anything that you think MIGHT be sciatica) - then you need to consult a doctor. SteveBaker (talk) 17:14, 15 December 2009 (UTC)[reply]

Thanks. Sciatica was what I was looking for. Regards.-Shahab (talk) 17:24, 15 December 2009 (UTC)[reply]

Oh well - it was a bumpy ride - but we got there in the end! :-) 18:09, 15 December 2009 (UTC)

Acetone/Water Mixtures: Flammability

Greetings! Acetone is a flammable liquid. 1 % acetone in water is not flammable. At what concentration (v/v or w/w) are liquid water/acetone mixtures flammable? And at what liquid mixture ratio is the vapor flammable? (everything under standard conditions). I have been searching, but these data seem to be hard to find. Thanks for help! Grey Geezer 09:21, 15 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One type of answer (which leads to more questions!) is "whatever liquid ratios give acetone vapor concentration between the lower flammability limit and the upper flammability limit". Assuming it's actually the evaporating (and rapidly so, given the heat of the flame) acetone that's burning, you need to know the Lower flammability limit. The added water means some of the heat is used to evaporate that rather than acetone (reduces the efficiency of the self-perpetuating flame) and to dilute the air/acetone vapor with water vapor (affects the lean/rich mixture required to burn). I have no idea the specifics for acetone, but those are "one level deeper" into how I understand the issues involved. DMacks (talk) 09:40, 15 December 2009 (UTC)[reply]

Depends on the liquid temparature too. My copy of the rubber company handbook has vapour pressure curves for acetone above mixtures of acetone water but in practice it is going to be tough to calculate, and flash points etc in reality depend heavily on geometry however we try to standardise them. The only help I can think of is that these kind of numbers are easily obtained for ethanol and ballpark acetone might be similar. Cold brandy is hard to burn warm brandy will sustain a flame easily. So brandy at say 20C (and 40 degrees proof which is 20% alcohol is marginal). Guess acetone might be something similar? --BozMo talk 10:06, 15 December 2009 (UTC)[reply]

I would be extraordinarily careful about any attempt to generalize from one flammable liquid to another. The boiling point of acetone is only 56°C, compared to ethanol's 78°C; at room temperature the vapor pressure of pure acetone (nearly a third of an atmosphere) is roughly triple that of ethanol. Meanwhile, the lower explosive limit of acetone (2.6-3.0%) is lower than that of ethanol (3.0-3.3%). What you might try searching on is something like air-water partition coefficient acetone. Google scholar or PubMed will turn up a number of results. I'm not in my office at the moment so I can't get at the journal articles that are hiding behind paywalls, but there are some likely hits there if you're coming from a university with suitable subscriptions. TenOfAllTrades(talk) 16:40, 15 December 2009 (UTC)[reply]

I further searched my question with lower flammability limit but still did not find the answer. It surprises me that this piece of data seems to be nowhere available. If TenOfAllTrades comes up with a number and a reference, I could look myself. Grey Geezer 11:52, 16 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs) [reply]

What are the arm blades of a preying mantis made from?

I've seen videos of the large preying mantises stabbing or slashing open rodents and birds with them. I suppose that they're probably made from a similar substance to the rest of the mantis's exoskeleton, but are they toughened or hardened somehow? Also, does the mantis have to do anything to keep them sharp? --95.148.104.205 (talk) 09:23, 15 December 2009 (UTC)[reply]

It may have been done initially with pun intended, but the proper spelling is praying, referring to the folded arms/prayer-like stance. DRosenbach ^{(Talk | Contribs)} 14:17, 15 December 2009 (UTC)[reply]

AFAIK, "blades" of the grasping forelegs are made of the same thing all insect exoskeletons are made of: chitin + protein matrix + calcium carbonate. Chitin by itself is somewhat similar to cellulose, but the addition of the other two components makes it much more rigid. Now, as far as the sharpening goes, mantises spend really a lot of time grooming their forelegs; but I am not sure at all if that contributes to the sharpness of the spines on the forelegs or is just meant to keep them clean. Anyway, keep in mind that any mantis molts a number of times before it reaches adulthood, and the entire exoskeleton is replaced every molt. --Dr Dima (talk) 10:34, 15 December 2009 (UTC)[reply]

Tree question

I am ok at felling trees in a given direction but I have a tricky one. The tree is on the bank of my moat, and is leaning over the moat by about 30 degrees (slowly falling). The moat is 6 m wide and the main tree truck is about 18m high (most of the canopy is gone so it approximates to just a trunk). I do not want to be fishing a tree trunk weighing a number of tonnes out of a 2m deep moat so I want to fell the tree so that the bottom of the fallen trunk is at a good distance from the stump. If I cut the tree at a given height above the ground how far away from the tree stump will the bottom of the trunk be at impact on the ground? Can I improve this by varying the slope of the cut? Any other ideas on how to get the trunk well over the moat?--BozMo talk 10:17, 15 December 2009 (UTC)[reply]

A photograph would help!

It doesn't matter how high up you cut it - the tree rotates about the point where you cut it until it's pretty much horizontal - and then pretty much falls vertically. If the fibreous wood doesn't break cleanly - then the trunk may even stay attached to the top of the stump and cutting it up higher just makes for a lot more grief - and makes what I'm about to suggest even more difficult. But a lot depends on how clean the break is and how top-heavy the tree is. IMHO, you're not going to get the trunk to fall more than maybe half a meter from the stump, no matter what you do.

If the geometry of the situation is as you say then you need to fell the tree so that if falls at right angles to this 'moat' - cutting it as close to the ground as is reasonable. If it's already leaning by as much as you say - you have no chance of making it fall in any other direction anyway.

If you're right about the dimensions then about 12 meters of tree will be on the far side of the moat with 6 meters dangling in fresh air across the moat. In theory - if the tree were of uniform thickness - the 12 meters out there on dry land would be plenty heavy enough to stop the other 6 meters from falling into the water. However - if the tree tapers strongly then it's possible that the bottom 6 meters will be heavier than the topmost 12 meters - and then the heavier bit might dip into the water - but at least you could loop a rope over the top of the tree and with a modest amount of weight - pull it down so it's horizontal.

Once it's down - if you don't have heavy machinery to haul the trunk 6 more meters until it's all on level ground - then I suggest that you prepare some rollers (maybe some nice round logs) on the far side of the moat for the tree to land on that would make it easier to pull it away from the water. If the tree's trunk is nice and smooth and round - you could probably use a fulcrum close to the water's edge to rotate the tree so that it's almost all on land anyway.

Whatever you do, don't start cutting the top of the tree into logs until the bottom is pulled clear of the water because as soon as you remove weight from the top of the tree - the bottom will be more likely to fall in!

Also, I would prepare for the worst by tying some heavy ropes or chains to the base of the tree a few feet above where you intend to cut it - BEFORE you cut it down - so that if it does end up in the water - you at least have something to haul it out by.

Good luck!

SteveBaker (talk) 14:06, 15 December 2009 (UTC)[reply]

The real worry about tree felling as far as I'm aware is if the tree doesn't just angle over still connected to the stump but breaks away, in which case the base of the tree would come towards you rather than go further over the water. So yes the best you can do is cut it near the base. If you can strip off the branches for the first 6 meters it mightn't be too hard to winch it out after you're finished. Or there may be some heavy canvas or a board you could put down to make it slide over the other bank easier. The only advantage I can see of cutting it higher up is that the bit over the moat will be lighter. Dmcq (talk) 14:21, 15 December 2009 (UTC)[reply]

Yep, its a big Ash and will split violently. But by the time it does the canopy must have momentum away from the bank. Perhaps if I undercut the far side and over cut the bank side second I can get the whip to go the right way. My guess is there is at least six or seven metric tonnes of trunk there though so the sliding bit ain't going to be easy. --BozMo talk 14:50, 15 December 2009 (UTC)[reply]

The base of the tree can indeed kick backwards (because the tree would 'naturally' try to rotate about it's center of gravity - not about the bottom of the trunk) - but if you do it right, you don't cut all the way through the trunk - you leave enough wood there to act as a "hinge" to prevent that from happening - and to give you enough time to shut your chainsaw off and get far enough away from the falling trunk! But that hinge also ensures that the tree rotates about the top of the stump - so that end of the trunk will end up close to (if not still attached to) the stump. When you get it right, that hinge breaks through completely just as the tree gets horizontal. The angle of cut of the "notch" that you cut on the side where you want the thing to fall is what makes that happen. The depth of the cut on the opposite side (which actually brings the tree down) is what ensures that the "hinge" is the right strength. There is an art to doing it right. I suppose the if the hinge broke through before the tree got horizontal - it might slide a little away from the stump - but I can't imagine that being anywhere near far enough to make a difference here. SteveBaker (talk) 14:54, 15 December 2009 (UTC)[reply]

I see lots of trees removed from backyards or parkways near homes, and the tree companies almost never just cut it down and let it fall when structures, fences, or sidewalks are anywhere near. Instead, they strip the tree down to the main trunk and a few main uprights by cutting branches and using pulleys tethereed to the main trunk to lower the branches to the ground. Then they cut the main trunk into short manageable sections which are lowered to the ground by pulley attached to the bucket the cutter works from. It is a few minutes work rather than one big boom. If you cut it down in one or two pieces, you would still need to cut it up for firewood or to go in the chipper. Standard tree removal would be easier than trying to cut up a tree which fell in a water filled ditch. Forget trying to be Paul Bunyan. A tree can spring back and kill the person cutting it. The impact of a large tree hitting the ground can jar nearby structures and knock things off shelves, or crack plaster. YouTube and America's Funniest Home Videos are full of unexpected outcomes of amateur tree felling. Call a professional, which might be affordable if you can afford something which needs a moat to protect it. Edison (talk) 15:07, 15 December 2009 (UTC)[reply]

Indeed - but we're told that this tree is 18meters tall(!) so climbing up it to bring it down in sections would be tricky - and it's leaning at 30 degrees out over a freezing cold moat...so lowering the topmost sections to the ground ain't easy either. Also, operating a chainsaw while balancing 50 feet off the ground in a dead tree over a cold wet moat is a life-threating situation that I absolutely won't recommend! SteveBaker (talk) 15:14, 15 December 2009 (UTC)[reply]

See Cherry picker. Pros do climb healthy trees, but more often the work safely from the bucket. The reach can be quite long, and the 3 foot sections can be lowered individually. 18 meters=18 pieces of wood. No big challenge or drama at any point. Edison (talk) 17:08, 15 December 2009 (UTC)[reply]

The critical question here (and something you don't KNOW the answer to) is whether the top 12m of the tree is heavier than the bottom 6m. If it is - then you need to have it land on a nice thin-but-hard fulcrum - close to the center of gravity of the tree. If you had it balanced perfectly on something like a large log - then the effort to rotate it 90 degrees so it's no over the water anymore would be fairly small - even if the weight of the trunk were many tons. Sadly, you can only guesstimate the center of gravity - so make your best guess and at least minimize the amount of pushing and shoving you'll need to do. Personally, I have a couple of block-and-tackle sets which allow me to haul very large tree trunks over short distances - so even if things didn't come out perfectly, it would still be a do-able job for one guy to get the entire trunk over dry land. But like I said - that assumes that the center of gravity of the trunk is more than the width of the moat from the cutting point. The lower you cut it - the more likely that is to be true. But there is absolutely nothing you can do to make a multiple ton tree jump six meters sideways and avoid the moat! SteveBaker (talk) 15:14, 15 December 2009 (UTC)[reply]

...and all of this discussion is why, if it is important for a tree to fall in a particular place (or especially if it's important that a tree not fall in a particular place) one should seek the services of a professional. The pros have all of the equipment and training to do the job right — and insurance, just in case they don't. Look in your telephone listings under "Arborists" or "Tree removal". A wise man knows when he's in over his head. TenOfAllTrades(talk) 16:08, 15 December 2009 (UTC)[reply]

...to be fair I have used tree surgeons for three of the larger dead trees I needed doing this year but those were ones which would have hit a road or an eleventh century church by our boundary. Aside falling in a moat or killing myself with a chainsaw (and I do quite a bit with a chainsaw myself) the worse case with this one is that I lose a load of firewood. The nearest building is a long way off. There may be some damage to a 900 year old scheduled moat too but that will happen for sure if I leave the tree to fall under its own steam. But Steve is probably right there is no way to get it to jump. --BozMo talk 16:43, 15 December 2009 (UTC)[reply]

If it is cut via cherry-picker bucket in short manageable pieces there is no damage to the ancient moat. I'm sure you are a smart feller and will consult a professional rather than random persons on the internet of unknown qualifications. Edison (talk) 17:20, 15 December 2009 (UTC)[reply]

I'll second that, the only posters in this thread you should be listening to are the ones telling you to get someone else to do it. Yes, you can get the tree to "jump" away from the stump—if the wood is sound you could probably fall it in any direction you wanted, despite the thirty degree lean. Do not pay attention to any of the advice above, those giving it have no idea what they are talking about.—eric 18:42, 15 December 2009 (UTC)[reply]

Its ok thanks. I asked for their advice because I wanted it and I am happy with some of the ideas. Sculpting trees in a town centre is a bit different from a country garden with lots of space and several hundred mature trees in it. But a cherry picker might be able to get there in the summer. --BozMo talk 18:57, 15 December 2009 (UTC)[reply]

EricR & Edison: Those are ridiculous statements. For starters, I have been dealing with trees and chainsaws off and on for about 35 years - and I know my way around a block-and-tackle - and it sounds like our OP has been there and done that too. Since we're both people who actually DO know what we're talking about, the advice to ignore all of this, throw up your hands and run to an overpriced professional is silly. This is a simple matter of physics - and that's exactly the kind of thing the science desk is here to discuss. We have medical disclaimers and legal disclaimers - but no tree-surgeon-disclaimers. I'd like to hear EricR's idea of how you get a multiple-ton tree to fall in the opposite direction to which it's leaning (at a 30 degree angle - over water, no less!) - or to jump 6 meters sideways. That should be good for a laugh. This is fairly elementary physics. Having said that, a Cherry Picker could let you take it down in sections if you can find one that can lean far enough out over the water whilst reaching up that high - and not damage the edge of the moat. SteveBaker (talk) 19:11, 15 December 2009 (UTC)[reply]

Not ridiculous at all, and civility is always appreciated. Edison (talk) 00:27, 16 December 2009 (UTC)[reply]

We certainly have no way of knowing if there is a way to drive a large truck near the tree. Foresters in my town have them in various sizes, small to HUGE with a very long reach. Tree felling is one of the most dangerous occupations, and even people who "have been dealing with chainsaws for 35 years" get killed in large numbers every year. Edison (talk) 20:25, 15 December 2009 (UTC)[reply]

There still remains a difference between the pro and even a seasoned amateur, and there's a potentially wide gap between someone who has 'been dealing with trees and chainsaws off and on' and someone who does the job every day for a living. My grandfather was a shop teacher for a couple of decades, then went on to build and operate a small sawmill and woodlot. He felled, cut, dried, and planed the cedar for my parents' back fence. When the time came to take down an awkwardly placed tree near one of his buildings, he still called a pro.

The pros have the right specialized tools (not just 'close enough'), and years of daily practice. The pro comes with a crew who know the job, and wear the right safety equipment; they're not your buddies from work (long on enthusiasm but short on experience, and who lack any sort of insurance coverage) who are in it for the free beer and pizza afterward. If the job requires really specialized equipment (like a cherry picker), the pro probably gets a discount on the rental. (The pro is also less likely to inadvertantly tip the cherry picker into your moat.) While I certainly would recommend avoiding an 'overpriced' professional (by all means get more than one quote!), I can't emphasize enough the value of real professional experience. TenOfAllTrades(talk) 20:35, 15 December 2009 (UTC)[reply]

Why don't we have tree-surgeon-disclaimers? Bus stop (talk) 20:57, 15 December 2009 (UTC)[reply]

The Schools Wikipedia says "not intended ... to be used in any way as a basis for behaviour" which would include trees... --BozMo talk 22:24, 15 December 2009 (UTC)[reply]

Steve, if it's a simple matter of physics then try this simplest of machines. All i can do here is relate a story about this guy. Teaching a class to professional fallers, he boasted that he could wedge over any tree that had good sound wood. Later, someone spotted a tall cedar, leaning way over backwards, and bet that this was one tree he could not wedge over. It was a set-up, he pulled a couple of high-lift wedges out of his bag and went to work. He would whittle away at the back cut, then tap on the wedges for a bit while watching the top of the tree. He added more wedges—driving some sideways near the holding wood and stacking others to get more lift. After about an hour of pounding on the wedges he had lifted the tree far enough that it fell in the direction he wanted—and won a steak dinner from the class.

Now a second-hand story really doesn't belong on the reference desk, but i hope it illustrates the difference between a professional and someone who, since they know a little bit of physics, thinks they can teach something as dangerous as timber falling. Based on your posts above, it sure doesn't sound like you've "been there and done that".—eric 01:10, 16 December 2009 (UTC)[reply]

There are nonetheless limits to what can be done with wedges, I use them a lot. But in this case the hero of the story would have drowned or died of hypothermia...--BozMo talk 13:07, 16 December 2009 (UTC)[reply]

And for a laugh, don't forget to go on youtube and search for tree felling accidents. I personally would agree that if there is any chance of damage to property, you should seek the help of an expert. Even if you are familiar with a chainsaw, if this is the 1st big tree you are cutting down, they say you learn from mistakes and in a situation when a mistake can be dangerous or expensive, it's better to let someone who has learned already do it. Vespine (talk) 23:48, 15 December 2009 (UTC)[reply]

We don't have tree surgeon disclaimers, but we do point out alternative methods that are sometimes used, and there is no reason we cannot counsel calling in someone with special equipment. What Steve says all sounds accurate if there are no nearby structures that could be harmed by an object weighting many tons falling on it. But many tree fellers have been surprised in unfortunate ways when the saw blade binds and they stick around too long trying to rescue it, or when it kicks back, or when the crown hits and it springs back. The timber industry has about the highest mortality rate among occupations. If you just fell the tree across the moat, it is likely to leave a depression in the other side of the moat when it hits. The portion hanging over the water after felling could be sawed off a few feet at a time in manageable hunks, and fished out by a rope you thoughtfully attached ahead of time. That part of the cutting could await warmer weather, so if you fall in the water is not freezing. Pros have lines, pulleys, and tree gaffs and are comfortable using them, as well as assessing the soundness of portions of a tree if climbing is chosen. They routinely take down much larger trees without drama, in small pieces. They have forestry bucket trucks which can reach a 95 foot working height or a lesser height with some lateral reach. Sometimes hard frozen ground is preferable to avoid ruts. Edison (talk) 00:27, 16 December 2009 (UTC)[reply]

I must admit thinking abut it I'm rather concerned that the poster thought the tree would jump in the direction it was falling rather than being worried about the trunk breaking off and coming back at him. If felling a tree you should have some idea of how the tree might behave as it falls and of possible problems. SO yes I'll add my voice to get a professional. Dmcq (talk) 01:24, 16 December 2009 (UTC)[reply]

Actually I've done a fair number of trees. The end of the trunk always ends up hitting the ground some small distance from the stump in the direction of the tree falling (unless the canopy catches other trees). Getting out of the way is not generally a problem especially as the last bit is always done with a sledge hammer and wedges rather than with a running chainsaw. Spring back is the commonest cause of fatalities with chainsaws though and I haven't done many at any angle. I will upload a couple of photos but its snowing now. --BozMo talk 12:27, 16 December 2009 (UTC)[reply]

That's good. The reason it will end up a little from the tree in the direction the tree falls if it is done right is that the trunk only parts from the stump after it has gone nearly horizontal, so yes as you say the momentum after that point will carry it away from the stump. I'd be surprised if you can get much distance at all that way, but I wonder at what angle one would get the best effect. There might be something about felling trees on the web about it. Dmcq (talk) 14:15, 16 December 2009 (UTC)[reply]

tree is in centre — tree hanging over moat

Here is a view of the tree from the corner of the moat, in high res you can just see ice on the near water. The tree is the obvious central one leaning over the water. Not remotely huge as trees go (about 75cm diameter trunk, so maybe 3-4 tonnes rather than 6-7 above) but still hard enough to lift. The angle at the base is close to 45 degrees and the trunk bends upwards, making wedges implausible even without the water. The moat is deceptively deep. There are quite a few similar trees. --BozMo talk 15:07, 16 December 2009 (UTC)[reply]

That looks nasty. The wood may not be good, bits may fall off, it may get lodged in a trees opposite, there's stuff all around it no nice way to retreat, not nice to clean up the bottom of the trunk so it doesn't get stuck in the moat. It looks to me like everything people warn about. And you've a load of them. I'd take professional advice, though I just had a look at a few videos and they looked pretty scary the precautions they weren't taking. Dmcq (talk) 15:52, 16 December 2009 (UTC)[reply]

Hmmm - a picture is worth a thousand words! Firstly - I did some measurements on your image - and there is no way that the chunky "trunk" part of the tree is three times the width of the water as you first said...it's at best twice as wide - probably less (we can't really see where the bank is opposite the tree - so it's almost certainly wider than I measured). Your estimate of a 30 degree lean angle is probably about right (although it's hard to get a decent vertical cue out of that photo). But also, the curve at the bottom of the trunk that makes it start out over the water almost horizontally makes it hard to cut a proper notch to get the tree to fall exactly the way you'd want - so it's probably going to go down at some non-optimal angle. That really changes things because now there is really no way that the bottom end of the tree can stay out of the water - and a very good chance that the whole thing will end up in the drink. Also, the way the bottom end of the trunk curves is going to be bad news for dragging it out of the water afterwards. Do you have access to a tractor or something? At this point, I think I'd tie some heavy chains around the bottom end of the tree - cut it down and let it fall where it may and then use the chains and a lot of brute force (and a heavy block & tackle or a tractor!) to pull it out of wherever it lands. It's either that or use a cherry-picker and take it down a bit at a time as others have suggested - but the terrain around there looks kinda rough for that kind of machinery to get in there and the lean of the tree and the placement relative to the water will make that be a difficult (and therefore expensive) operation. SteveBaker (talk) 19:30, 16 December 2009 (UTC)[reply]

Fair enough. It was easy to get the height (I can do simple algebra) but the width of the water was a guess and it could be 7m. I do have an Ordnance Survey site map from the listing somewhere. But back to my first idea: what happens if I cut it six foot up and a fair way over the water?--BozMo talk 19:43, 16 December 2009 (UTC)[reply]

Movement of the sun and moon around the sky

So, in the Northern hemisphere, the sun rises in the east, moves in a clockwise direction through the sky (and is at its midday peak in the south) and sets in the west. The moon does the same. Am I right so far? So what happens in the southern hemisphere? Does the sun still rise in the east? Is it at the north at midday? Does it go in an anti/counter-clockwise direction to set in the west (if it sets in the west?)? And what happens on the equator?

In the Northern hemisphere, stars move around the Pole Star - but what direction do they circle in - clockwise or anti/counter-clockwise?

Thank you for helping.81.159.89.69 (talk) 11:44, 15 December 2009 (UTC)[reply]

The cause for all these apparent motions, including star movement, sun rise, and sunset, is Earth's rotation. (The moon also adds a non-negligible extra detail due to its orbit around us, and the Sun also adds a smaller variation because of our orbit around it). But the most important factor here is Earth's rotation. Since Earth's rotation direction is the same everywhere on Earth, the apparent rise of the sun and moon are always in the east; the apparent direction is always the same - counterclockwise if you're facing north (clockwise if you're facing south). In the unique case of polar regions, the midnight sun throws another neat variation, in that the summertime sun never gets low enough to sink below the horizon; but it still "wobbles" in a circular path. The equator doesn't really behave very specially, except that the sun is directly overhead, approximately at the zenith, on noon of the equinoxes. As far as where the sun is at its midday peak, this depends on your latitude and the current season. Nimur (talk) 13:25, 15 December 2009 (UTC)[reply]

edit conflict Because, from a bird's eye perspective of the plane, so to speak, of our solar system, the earth rotates on its axis in a counter-clockwise fashion, the celestial entities (sun, moon, planets, stars) seem to orbit us in a clockwise fashion. Therefor, things rise in the east and set in the west. For one living in the northern hemisphere, solar/lunar "orbits" manifest as short days, with rising and setting occurring south of due-east and -west and the celestial entities don't travel too much into the southern sky. For the same northern hemispherer, summer manifests as long days, with the celestial bodies rising way north of due-east and setting way north of due-west and traveling three sides of the sky (east, south + west). Mid-day, by definition, presents as the sun in the exact middle of the sky in an east-west dimension, but the north-south aspect of the suns position at mid-day will depend upon the time of year (n.b. mid-day here is defined as the time from sunrise to sunset divided by 2). I will not speculate about what occurs in the southern hemisphere, because its quite easy to allow a minor error in calculation to become a tremendous error in conjecture. DRosenbach ^{(Talk | Contribs)} 13:30, 15 December 2009 (UTC)[reply]

Another interesting bit about latitude and the sun's midday position: it's a generalizable rule that the sun is southward in the northern hemisphere and northward in the southern hemisphere, unless you're in the tropics. Between the Tropic of Cancer and the Tropic of Capricorn (those lines of latitude equal to the Earth's angle to the ecliptic), this rule can be broken. At the northern summer solstice, all of the northern hemisphere south of the Tropic of Cancer sees the sun to the north at midday. In fact, at the equator, the expected lengths of day and such get extremely odd: the sun is highest in the sky near the equinoxes, lowest at each solstice. At Quito, Ecuador, the longest day of the year is near the December solstice (no surprise), but there's another maximum at the June solstice, and the minima are in April and August.[14] I expect that shift from the equinoxes is driven by the Earth's orbital eccentricity (the Earth is farther from the sun in June than in December). — Lomn 14:07, 15 December 2009 (UTC)[reply]

It's altogether easier to imagine that you're standing on the surface of a spinning ball - with everything else being more or less stationary! The ball takes 24 hours to spin once. (Which is unsurprising - because that's really what's happening.) SteveBaker (talk) 13:45, 15 December 2009 (UTC)[reply]

They say a picture is worth a thousand words, in this case an animation is even better. Download an open source application called Stellarium (computer program) and have a play. Firstly set your own location and play with the time controls, this will give you "bearings" of where and how the sun rises and sets, and where the stars rotate. Once you have a grip on what you are looking at, change your position to anywhere else in the world, the poles, the equator, anywhere in between, and play again with the time controls. Vespine (talk) 23:19, 15 December 2009 (UTC)[reply]

What happens when you mix hydrogen peroxide and liver?

Biology —Preceding unsigned comment added by 68.146.63.129 (talk) 15:04, 15 December 2009 (UTC)[reply]

In respect to physiology or culinary arts? H₂O₂ will bubble with oxygen release when contacting the blood of the liver (liver is very bloody, as it contains vascular sinusoids). DRosenbach ^{(Talk | Contribs)} 15:20, 15 December 2009 (UTC)[reply]

Depends how the liver is prepared. This is a common high-school bio experiment, so I'll not comment further. DMacks (talk) 17:44, 15 December 2009 (UTC)[reply]

I let myself correct your link, Drosenbach. --Ouro (blah blah) 18:00, 15 December 2009 (UTC)[reply]

I let myself correct your grammar, Ouro. :) DRosenbach ^{(Talk | Contribs)} 19:29, 15 December 2009 (UTC)[reply]

I had to check, what an error! Thank you! --Ouro (blah blah) 17:46, 16 December 2009 (UTC)[reply]

Earth Changes

How valid are some of the predictions in this article? Are they even possible? Are there any notable scientists today who vaildate some of the changes predicted here? --Reticuli88 (talk) 15:40, 15 December 2009 (UTC)[reply]

Not very - though I hasten to say it is a good article dealing well with the subject. The last couple of lines answer most of your question: "Prophecies of Earth changes have been described as a form of scientism, in which terminology and ideas borrowed from science are used to rationalize non-scriptural apocalyptical thought based on visionary experiences. David Spangler, a leader of the Findhorn Foundation spiritual community, described prophecies of Earth changes as an expression of collective fear and anger, rather than as foretelling of actual future events."

Clearly some predications may sometime come to pass; if sea levels rise, if there is a major earthquake or volcanic eruption. But the absence of real scientific underpinning tends to be the give-away. --Tagishsimon (talk) 15:49, 15 December 2009 (UTC)[reply]

How do we know the speed of light is constant?

We can measure the speed of light and observe that it has not changed between our measurements, but how do we know that the speed of light has not changed over the course of time? Or how do we know that the speed of light is not a local phenomenon, resulting in our speed of light being at least a little different then the speed of light in another star system or galaxy? 65.121.141.34 (talk) 15:45, 15 December 2009 (UTC)[reply]

The questions you ask are good ones, and physicists do think about what effect a changing speed of light would have, and whether we could observe such variation. While there is no good evidence of a variable speed of light, we do have an article on the topic: Variable speed of light. -- Coneslayer (talk) 16:23, 15 December 2009 (UTC)[reply]

The deal is that the speed of light is built into so many other parts of physics that the way things like the fusion reactions in stars work would be noticeably different if a different speed of light applied. When we look out at things that are a long way from us - we're seeing them as they were a long time ago. If the speed of light was significantly different than it is today - we'd be able to tell because we'd see things like spectral lines representing the emission and absorption frequencies of common elements being wildly different than they are today - or stars of a particular color having different 'ingredients' than stars of that color that are close to us. That same reason also explains how we know that the speed of light is the same in places a long way from us. I suppose that VERY small changes might somehow sneak by - but it would have to be a rather insignificant difference for it not to be somehow measurable. SteveBaker (talk) 17:04, 15 December 2009 (UTC)[reply]

The speed of light was also measured from a binary star, and no difference in the speed was detected when the star was moving toward, or away from us. I believe this was the first direct evidence of the constancy of the speed light. Ariel. (talk) 07:30, 16 December 2009 (UTC)[reply]

See Michelson–Morley experiment for that. --Stephan Schulz (talk) 08:07, 16 December 2009 (UTC)[reply]

At what distance was the binary star? Would a change of 0.1% per 1,000 lightyears be detectable using that method?

Hold on - this question got derailed in the middle there. This isn't the usual question of: "Is the speed of light independent of the motion of the observer relative to the source?" (Yes, remarkably, it is). That's what you'd use a binary star for - and it's what Michelson & Morley proved. No - this question asks whether the speed of light the same now as it was (say) a few billion years ago - and is it the same here, in our solar system as it is in (say) a neighboring galaxy? Michelson & Morley didn't attempt to show that - and a binary star doesn't help you much with that either. As I said - you really have to look at the secondary effects of the speed of light - comparing the diameter of the event horizon of a black hole to it's mass, for example. As I said before, I'm pretty sure that any change in the speed of light at long distances or in the distant past would produce extreme weirdnesses in the spectral characteristics of distant objects that we simply aren't seeing. So I believe it's fairly safe to say that we don't believe that the speed of light has ever been different or is different in different places. SteveBaker (talk) 03:22, 17 December 2009 (UTC)[reply]

Interpreting life expectancy

If I am a member of a group with life expectancy of 80 years and I am 25 years old, should I expect to leave more or less 55 years? Or does it means that children born today could expect to live more or less 80 years? Or people dying today are on average 80 years old?--ProteanEd (talk) 17:49, 15 December 2009 (UTC)[reply]

Given the development of medicine and technology you might live past one hundred. Given the development of ways to make others suffer, hell knows. --Ouro (blah blah) 17:53, 15 December 2009 (UTC)[reply]

WMDs have been around for decades and, in the grand scheme of things, very few people have been killed by them. I don't think their existence has a significant impact on life expectancy. --Tango (talk) 17:59, 15 December 2009 (UTC)[reply]

Usually life expectancy refers to life expectancy at birth. So it is talking about people born today. If you want more detailed information you need a life table (there are life tables available online for free for various populations) - that will show how long people born at different times can expect to live. Life expectancy increases as you get older because there is no longer a chance of you dying before your current age. So, if life expectancy when you were born was 80 years then you can expect to live longer than 55 years (assuming you are an average members of that population in terms of lifestyle, etc.). Life expectancy for people born now doesn't say much about how long you will live. --Tango (talk) 17:59, 15 December 2009 (UTC)[reply]

Bear in mind that such a life expectancy is the calculated average expected for the group overall. There are always variations above and below the average, and unforecastable accidents (such as terrorist bombs) may or may not have been taken into consideration. The predicted life expectancy of the cadre you are in cannot say anything very definite about your individual life expectancy; a detailed individual health and lifestyle analysis would be necessary for that, and-- Oops! Watch out for that meteorite!! 87.81.230.195 (talk) 19:42, 15 December 2009 (UTC)[reply]

I strongly suspect that terrorist bombs and meteorite strikes are but a minuscule impact on life expectancy. 65.121.141.34 (talk) 19:51, 15 December 2009 (UTC)[reply]

I agree. I wrote this on Talk:Main Page but it's of relevance here:

This is somewhat morbid/grim so don't read if you are uncomfortable with that but as has been kind of hinted at, deaths due to natural disasters can relatively easily exceed death tolls due to terrorist attacks or building fires, and unfortunately relatively often enter into the quadruple digits (look at the earthquakes list for example [15]). Just this year we had the 2009 Samoa earthquake and resulting tsunami (death toll possibly exceeded any single event you mentioned) which occured on the same day as the 2009 Sumatra earthquakes (alone over 1000). And a few weeks ago we had 2009 Jeddah floods which was in the triple digits (and deaths during the Hajj are unfortunately not uncommon). Can't remember if we had Typhoon Ketsana (2009) but that's over 600 if we did (and worse therefore then any other terrorist attack so far bar September 11 [16]). Earlier this year, I'm pretty sure we had the Black Saturday bushfires which again possible resulted in more deaths then any single event you mentioned. As Boz said, the 2004 Indian Ocean earthquake and resulting tsunami is the worst that we've had. Hopefully we'll never exceed that in a long time but unfortunately it could happen, List of natural disasters by death toll is perhaps poignant reminder of that. P.S. Just to be clear, I'm not trying to downplay the impact of terrorist attacks simply pointing out that in terms of deaths, they pale in comparison to many natural disasters

Of course even natural disasters are a small percentage of deaths. In much of the developed and developing world, you much more likely to be killed in an road accident for example. P.S. The events that I didn't name there are the recent Baghdad bombings, the recent Pakistani bombings and the night club fire. Nil Einne (talk) 13:18, 16 December 2009 (UTC)[reply]

And then, of course, there is old age. The vast majority of people in the developed world die of age related diseases. The majority is not so vast in the developing world, but I think it is still a majority. --Tango (talk) 16:58, 16 December 2009 (UTC)[reply]

See actuarial table. I believe the article (and the first actuarial table you read) will answer your question fully. Comet Tuttle (talk) 22:53, 15 December 2009 (UTC)[reply]

Why am I able to see depth in this video?

what is the science behind this please. --Reticuli88 (talk) 18:21, 15 December 2009 (UTC)[reply]

When you cross your eyes and get the images (which are slightly different) to overlap what is happening is one eye is looking at one image and the other eye at the other image and brain is interpreting it as if they are both looking at the same thing. Your eyes seeing slightly different things is one of the main ways we perceive depth (see binocular vision). --Tango (talk) 18:42, 15 December 2009 (UTC)[reply]

We have an article on these of course: stereogram. J kasd 18:48, 15 December 2009 (UTC)[reply]

Do you know where on the internet is there videos of moving stereograms? --Reticuli88 (talk) 18:55, 15 December 2009 (UTC)[reply]

A collection of stereograms can be found here. Scroll to the bottom of the page for 2 animated examples. Pim Rijkee (talk) 22:17, 15 December 2009 (UTC)[reply]

We have one here. It's a pretty interesting one since you can't tell what it is until you cross your eyes. (Besides reading the title.) J kasd 04:32, 16 December 2009 (UTC)[reply]

plastic laminate

what makes up laminating plastic material?are the chemicals safe to use in the home ? —Preceding unsigned comment added by 173.88.240.10 (talk) 18:50, 15 December 2009 (UTC)[reply]

For woodworking, most "plastic" laminate is made of layers of paper bound together with epoxy. The chemicals used to bind this to the surface often have volatile chemicals in them and should not be sprayed without ventilation. If you're referring to the thin, sticky plastic used to cover books and posters, this is usually made of PVC with a layer of adhesive. Laminators using heat to make name badges or other objects may pose a risk if you burn the plastic. There are many ways to use a laminate material, so without more specific uses, the safety can't be evaluated effectively. Caltsar (talk) 17:07, 16 December 2009 (UTC)[reply]

Gallium

Where's a good place to buy gallium online? ----J4\/4 <talk> 19:39, 15 December 2009 (UTC)[reply]

It's available on Ebay. 10 gram lots of claimed 99.9999% pure Gallium have sold in the recent past for $29.11 and 100 g lots for $113 from a UK supplier. Also see Answers.com for the same question. [17] sells it for $1250/kg. Edison (talk) 20:14, 15 December 2009 (UTC)[reply]

But couldn't the sellers on ebay be lying? Also, is gallium toxic? ----J4\/4 <talk> 20:16, 15 December 2009 (UTC)[reply]

Toxicity for the pure element is still indeterminate for skin contact. 65.121.141.34 (talk) 20:34, 15 December 2009 (UTC)[reply]

Sellers on Ebay can always be lying. But if it is someone who sells a lot of similar products and has a very good rating, they are probably not lying. --Mr.98 (talk) 21:23, 15 December 2009 (UTC)[reply]

How would they check? Do gallium buyers generally have the equipment required to test its purity to that level? Vimescarrot (talk) 21:34, 15 December 2009 (UTC)[reply]

I assume people buying 99.9999% pure gallium are probably doing something with it that requires very pure gallium. I have no idea what that would be. If pure gallium were indistinguishable from garbage then they wouldn't need to bother buying pure gallium. Rckrone (talk) 22:02, 15 December 2009 (UTC)[reply]

United Nuclear has Gallium chunks available. Expensive, though—$15/g. --Mr.98 (talk) 21:22, 15 December 2009 (UTC)[reply]

Well clearly a home user is not going to be able to differentiate between 99.9% purity or higher -- though 99.5% purity could cause a significant change in physical characteristics that might well be noticeable. A quick search on Google does show Journal articles referencing gallium used at 99.999% purity, sourced from one of the main chemical suppliers, so I would accept that gallium at this purity does exist. There must be a particular feature of gallium or its extraction that makes it relatively easy to manufacture it at this relatively high purity. For other metals the difference between 99.5% purity and 99.99% purity could typically be a factor of 10 in price. Rjwilmsi 23:17, 15 December 2009 (UTC)[reply]

Do none of you ever bother to read the articles? :-P From Gallium

Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[17] An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling."

&

The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal"

Then there's these in the external links pure Gallium crystals ~99,9999% picture in the element collection from Heinrich Pniok & Price development of gallium 1959-1998. And in the article, I noticed

High-purity gallium is dissolved slowly by mineral acids.

which may or may not be a good way to test purity.

However I have to admit I'm sceptical of these Ebay sellers. You can get a decent idea from feedback but it's far from perfect. Given the prices, I wonder if these people really need such high purity or are just buying it because it's cheap. What are they even using it for? Would someone in a research lab or other place where they may really need such high purity actually buy from eBay? It seems to me they're more likely to buy from an established supplier outside of eBay. Maybe the people know the claims are probably bullshit they just don't care? In other words while it may very well be that purity, I'm don't think we can go solely by the feedback. Taking a look at what else the people have purchased may help, since it may give you a hint what they're likely to be using it for.

Also looking at the feedback, e.g. if it's largely "delivered on time, looks great in my metal collection" or "received today, now I can get started on my perpetual motion machine" I wouldn't trust them to know what the purity is. If it's "just confirmed with mass spec and NAA that it's really 99.9999% purity" [18] [19] ref(yes I know this isn't gallium metal) or "wow I didn't really expect it to be genuine 99.9999% purity but I the results from the X-ray diffraction, SEM, AA, BET surface area, and ICP Spectrometry confirms it is" ref(slightly OT but maybe those will be useful to test the purity tool); well then you can think maybe they do know what they're talking about.

I also came across [20] which may be of interest Nil Einne (talk) 15:10, 16 December 2009 (UTC)[reply]

Southern Hemisphere deciduous forests

Why doesnt the southern hemisphere have more temperate broadleaf decidous forests?

There are some in South America (southern Chile and Argentina), and one deciduous shrub in Tasmania, Australia (Nothofagus gunnii), but apart from that, there isnt much. Whats preventing southeastern Australia (New South Wales and Victoria) from having a deciduous forest? The climate there definitely calls for one...

And what about Argentina, further north in the region between the Parana and Uruguay Rivers, and the Buenos Aires province. The climate there also calls for a deciduous forest, albeit different from that of the more southerly one. We can perhaps draw a comparison between the climate of that region (Parana...etc.) and that of the southeastern U.S. (Louisiana, Mississippi, Alabama, Georgia). Those states are predominantly made up of deciduous forests, with a few pine forests also thrown in. So, why doesnt the southern hemisphere have more deciduous forests? Any ideas...? Thanks! —Preceding unsigned comment added by 201.21.180.57 (talk) 21:21, 15 December 2009 (UTC)[reply]

How would deciduous trees of any kind spread to the Southern Hemisphere? They would have to spread gradually through the tropics from the Northern Hemisphere, and they don't survive in the tropics. So, barring human transport, there's no mechanism by which such plants would migrate to the Southern Hemisphere. --Jayron32 21:49, 15 December 2009 (UTC)[reply]

That argument is not valid, as deciduous forests are found all over the world: the question is, why there are more in the Norhern Hemisphere. First of all, deciduous forests are confined to regions with a temperate climate: that is, a C classification in the Köppen Climate classification. This climate is found in the parts of the southern hemisphere you describe: SE Australia, Rio de Janeiro region. Remember, most of the earth's land mass is on the northern hemisphere; together with the Cf-classification needed for temperate forests, suitable areas are limited. Here you can check the area where temperate forests would grow (if soil conditions are suitable). Not nearly as much as on the northern hemisphere. Another major problem is deforestation, as the Cf climate regions are often places for settlement and have huge urban areas (SW China, SE Australia, Rio de Janeiro region). You can see the impact on this map. Thus, limited landmass, little Cf-climate area and deforestation make for less temperate deciduous forests on the Southern Hemisphere. Pim Rijkee (talk) 22:13, 15 December 2009 (UTC)[reply]

I think the argument is valid, though limited landmass/climate area is probably a more major issue here. Jayron is right that most seasonal trees cannot survive the tropics "as they are", though it's obvious that there was a lot of exchange between hemispheres during the most recent ice age (i.e. subarctic varieties had moved so far south, and the tropics were probably so cool as to allow some of the northern varieties to travel to the south), and probably every cold period previously. Because of the large subarctic landmasses in the north, subarctic varieties of forest trees are more likely to produce successful genetic variations, and thus they will survive better in competition with other plants, preserving more species and higher populations. The southern subarctic varieties don't have as much suitable environment, so they come under more competition from non-subarctic varieties; that is as long as the gene pool isn't rejuvenated by transports from the north. 219.102.221.182 (talk) 06:20, 16 December 2009 (UTC)[reply]

December 16

Nuclear Warfare

How much time does it take for nuclear radiation from a bomb to decay to a safe level? —Preceding unsigned comment added by Cborgen (talk • contribs) 00:05, 16 December 2009 (UTC)[reply]

That's going to depend heavily upon how one chooses to define a 'safe' level — does one mean a level that won't cause acute, fatal radiation sickness, or a level that won't appreciably increase one's lifetime risk of cancer? Those two numbers are going to be rather different, and they're going to heavily depend as well on the yield and location of the bomb. (An air burst will generate less fallout than a bomb detonated close to the ground, for instance.) Finally, do you want to know when it's safe to approach ground zero (the point where the bomb detonated) or just somewhere within a certain radius? Whether one is upwind or downwind of the blast will make a significant difference to one's safety.

All of that pretty much boils down to 'it depends'. You might find the information (and references) in our articles on Nuclear fallout and Effects of nuclear explosions on human health to be helpful, though. TenOfAllTrades(talk) 00:17, 16 December 2009 (UTC)[reply]

There are a number of radiation threats from a nuclear bomb. We might characterize them roughly as so: The first is the pulse that you get from the weapon itself—which will kill you if you are within a certain radius (the size of that radius varies with the yield of the bomb). The second is the radiation caused by short-lived fission products. This is intense (will kill you if you are near it) but relatively short-lived—this is what a fallout shelter is designed to protect you from (if you stay underground for two weeks, you miss most of this). The third is the long-term radiation caused by other fallout. This is the sort of thing that will not kill you immediately, but over the course of living near it, ingesting it, etc., will raise the background rate of cancer appreciably, cause birth defects, etc. How much fallout is created (both the second and third types here) varies with the yield of the bomb, the design of the bomb (some bombs are "dirtier" than others), and the height of where the bomb goes off. --Mr.98 (talk) 00:53, 16 December 2009 (UTC)[reply]

Stars, black holes, and motion...

From an article about a recently re-analyzed black hole - The outermost layers of the star are being siphoned by the black hole. The swirling gas forms a hot plasma disk around the black hole before it disappears, and the process emits a lot of X-rays and radio waves. The part in bold, can we observe that in motion? If Hubble takes a look at that pair and then looks back a day later - can we see a change? a week/month/year later? It's easy for me to visualize swirling masses of plasma being sucked off/out of a star and into the black hole, but I'm VERY curious about the timescales involved. Surely observation of the process-in-motion is possible with instruments, it being only a question of resolution? Are we there yet? Can we watch this happening or is it still the "snapshot" approach? 218.25.32.210 (talk) 08:05, 16 December 2009 (UTC)[reply]

It will most likely be a continuous stream, like in this image (which has a white dwarf, rather than a black hole, but the same concept). I think it is mostly an assumption based on the X-rays - they indicate that it is very hot and there aren't many ways of getting things that hot. Gas spirally into a black hole is one of the few things that can. --Tango (talk) 16:35, 16 December 2009 (UTC)[reply]

The dynamics of accretion disk material can be studied through spectroscopy; the material's velocity gives rise to an observable Doppler shift. See for example Time-resolved spectroscopy of accretion disks in ALGOLS. -- Coneslayer (talk) 16:48, 16 December 2009 (UTC)[reply]

To be clear - we don't have any photographs showing this pretty swirling thing happening. We can only deduce that from other data. Hence, no - the Hubble can't take a pair of pictures and show it happening. A better question is whether the spectroscopic data shows that change. SteveBaker (talk) 17:43, 16 December 2009 (UTC)[reply]

There ARE measurements of radiation from the innermost accretion disk of a BH which indicate that there are enormous velocities involved: the amplitude of the radiation had a frequency of several hundred Hz superimposed. That means that matter circles the BH just above the event horizon several hundred times per second, see eg [21]. --Ayacop (talk) 14:40, 17 December 2009 (UTC)[reply]

Condensation Between Propanoic Acid and 3-Aminopropanal

Hello. How is the main product of the condensation between propanoic acid and 3-aminopropanal named according to IUPAC nomenclature? I think that the aldehyde group in 3-aminopropanal does not react and naming the main product 3-formyl-N-propylpropanamide is ambiguous since the aldehyde group can be on the alkyl chain or the 'amide' chain by the naming alone. Is the main product a double-branched amine or a single-branched amide? Thanks in advance. --Mayfare (talk) 09:15, 16 December 2009 (UTC)[reply]

First you have to figure out the structure (what part(s) react, what the connectivity of the product is), then worry about how to name it. When you have branched-branches, there are specific ways to express what is branched off of what, for example, saying "3-formylpropyl" or "3-formylproanamide" to explain which 3-carbon chain is formylated. Also be careful to use hyphens or parentheses to separate groups "N-propyl-propanamide" means "propyl on N of propanamide" whereas "N-propylpropanamide" sounds like there is a "propylpropanamide" on the N of something else. DMacks (talk) 09:53, 16 December 2009 (UTC)[reply]

Total weight of all insects in the world

If you gathered all the insects in the world together, how much would they weigh in total? --OpenToppedBus - Talk to the driver 11:47, 16 December 2009 (UTC)[reply]

Some background to the question. I've seen lots of sites saying things like "the total weight of insects on the planet is more than all other species put together" or "the total weight of insects destroyed by spiders in a year exceeds the weight of the human population". Last night I heard Johnny Ball claim that for every human on the planet, there are enough insects to equal the weight of seven African elephants. But I can't seem to find any evidence to back any of this up. --OpenToppedBus - Talk to the driver 12:41, 16 December 2009 (UTC)[reply]

Our article biomass (ecology) contains estimates that the total mass of ants is 9–90 times the total mass of humans. I don't know what proportion of insects are ants. Algebraist 13:00, 16 December 2009 (UTC)[reply]

Ant says that ants "may form 15–25% of the terrestrial animal biomass". Algebraist 13:03, 16 December 2009 (UTC)[reply]

And it looks like ants may be about half of insect biomass. So let's say insects are roughly 20-200 times the biomass of humans. Worldwide, an average human is roughly 50kg, so there's 1,000 - 10,000kg of insects for each of us. Even taking the top end, that would still be barely more than an elephant each of insects. So it looks like Johnny Ball was wrong about that last night, as about so much else. --OpenToppedBus - Talk to the driver 14:01, 16 December 2009 (UTC)[reply]

According to this page: http://www.entsoc.org/resources/faq.htm?/print#triv1 there are about 10^19 (10 quintillion) insects in total. Multiply by whatever you think is the average weight. Mytg8 (talk) 14:22, 16 December 2009 (UTC)[reply]

Atoms

why are atoms colourless, despite colour originally containing atoms has colour?

colour or paint is made from various compounds.Molecules combine to form compounds.a moleculeis formed by the combination of atoms.As we know that atom retains its identity throughout chemical change.therefore atoms should have colour —Preceding unsigned comment added by Omkar2510 (talk • contribs) 12:54, 16 December 2009 (UTC)[reply]

Colour comes from the interaction of a substance with light. Exactly how it interacts with light depends on the structure of the material, and in particular on the legal state changes for electrons in the material. These are different for individual atoms, molecules, and crystals. But yes, atoms do preferably emit and absorb light at certain frequencies - see emission spectrum. In that sense, they do have a colour (but one that is different from most of the compounds it forms, and different in non-trivial ways). --Stephan Schulz (talk) 13:39, 16 December 2009 (UTC)[reply]

The OP is claiming that since paint has color and is made of atoms than atoms must have colors as well. I just want to point out the fallacy in this logic with an analogy: Humans have thoughts and are made of cells. Does that imply that cells must have thoughts? Dauto (talk) 14:26, 16 December 2009 (UTC)[reply]

We've got articles on logical error: fallacy of division or fallacy of composition, depending on how you look at it. --Sean 15:34, 16 December 2009 (UTC)[reply]

As Stephan notes, the behaviour of matter can be very different when one compares bulk solids with nanomaterials with individual atoms. Consider gold as one example. What colour is it? Well, obviously it's gold. Take a chunk of it; it's gold. Hammer it out into thin sheets; it's gold. Put flakes of it in your drink; it's Gold...schläger. Makes it into tiny beads a hundred nanometers across, and it's...bright red. Whoops. Take it down to single atoms in a vacuum, and you'd get the sharp absorbance spectrum that Stephan describes. Per Dauto, the whole is often very different from the mere sum of its parts; the behaviour of large numbers of atoms tends to be very different from the behaviour of single atoms. TenOfAllTrades(talk) 14:45, 16 December 2009 (UTC)[reply]

To pick a more commonplace example - carbon is black - right? ... Unless it's a diamond when it's completely transparent. It depends on the crystalline nature of the material - not just what it's made of. SteveBaker (talk) 17:39, 16 December 2009 (UTC)[reply]

See HOMO-LUMO gap. The colour behaviour of a substance is determined by its chemical environment, e.g. electron charge density and the relative energies of various electronic orbitals. John Riemann Soong (talk) 18:57, 17 December 2009 (UTC)[reply]

combined serial and parallel circuits

In a combination of serial and parallel circuits, such as this one, am I correct to conclude that all three lamps shine equally brightly? My reasoning is that a and b/c are connected serially, so both a and b/c should get half of the voltage of the cell. B and c are connected in parallel, so they each get the full amount, thus all three each get half of the voltage of the cell. (I know this might sound like homework, but I am just trying to understand more about electricity and I have no teacher whom I can ask...) Lova Falk (talk) 14:41, 16 December 2009 (UTC)[reply]

I'm not going to answer straight out, but I will ask — how much current flows through each lamp? TenOfAllTrades(talk) 14:47, 16 December 2009 (UTC)[reply]

As far as I understand, lamp a gets twice the current compared to lamp b and c. Lova Falk (talk) 14:55, 16 December 2009 (UTC)[reply]

Assuming that all three lamps are identical, yes. Now, by Ohm's law, what does that tell you about the voltage drop across lamp a versus across lamps b and c? TenOfAllTrades(talk) 15:16, 16 December 2009 (UTC)[reply]

Do I understand correctly that the resistance of each lamp is the same, irrespective of the way it is connected? In that case, the voltage of lamp a should be twice the voltage of lamps b and c. Lova Falk (talk) 16:03, 16 December 2009 (UTC)[reply]

Yes, resistance is an intrinsic property of an item (in basic circuit scenarios, anyway). You could also approach the solution by combining lamps B and C into a single unit BC (via the equation for parallel resistance) and then solve the series system of A and BC. — Lomn 16:16, 16 December 2009 (UTC)[reply]

Bingo. Sounds like you're on your way to a final answer, now. From here (and for more general cases like multiple components in parallel or unequal resistances/loads) you'll probably want to have a look at the formulae and derivations in Resistor, Series and parallel circuits, and Kirchhoff's circuit laws. TenOfAllTrades(talk) 16:44, 16 December 2009 (UTC)[reply]

Thank you! Lova Falk (talk) 17:12, 16 December 2009 (UTC)[reply]

This is a little late, but I should point out that the resistance of a real lamp is not a constant. The resistance is almost zero when the lamp is cold, but goes up very much when hot. So don't try to calculate the wattage of a lamp by measuring the resistance when off, and using ohms law.

The second implication is that if you actually made the circuit in the diagram with real lamps, you will not see what you expect. The lamp with less current flowing through it will not be as hot, so it's resistance goes down. Normally more current will then flow (heating it up) - but when it tries, the other lamps get hotter, increasing their resistance. So the current stays low, and the lamp with less current flowing through it will actually by dark, rather than half on. Ariel. (talk) 08:43, 18 December 2009 (UTC)[reply]

new planets

I have questions after reading http://news.bbc.co.uk/2/hi/science/nature/8414476.stm but don't know where to look in Wikipedia. (1) On a planet five time the mass of earth, what would the gravity be like? What would it be like to walk on the surface? (2) What are the odds of any given planetary atmosphere being breathable by humans? (3) How long would it take to travel to a planet 28 light years away using current technology? Thank you for helping. —Preceding unsigned comment added by 70.29.47.136 (talk) 15:05, 16 December 2009 (UTC)[reply]

At 5 times the mass of earth, the gravity would be 5 times as great, and you'd feel 5 times as heavy. See Newton's law of universal gravitation
Probably not very great. The existance of plants is prerequisite for an atmosphere to be breathable by humans and other animal life. Free oxygen is way too reactive to exist unless a system is actively producing it, and on Earth, it is the existance of plant life that creates and maintains the oxygen in our atmosphere. So, unless plants are already there, there will not be a breathable atmosphere.
24 light years = 2.65 x 10¹⁴ kilometers. So you would just need to calculate the maximum speed of a rocket using current technology, and do the math. --Jayron32 15:33, 16 December 2009 (UTC)[reply]

(edit conflict)Gravity depends not just on the mass of the planet, but also the radius of the planet, and is dictated according to the equation Gm/r², where G is the Gravitational constant, m is the mass of the planet, and r is the radius of the planet. The article seems to conflate size with mass, and gives unclear numbers, so I couldn't say much about what it would feel like there.
Who knows, although probably unlikely. Europa has plenty of oxygen, for example. On Earth, Oxygen came into existence largely as a result of photosynthetic life, which could indicate it isn't likely to occur elsewhere. Oxygen was toxic to early life, so much so that planets with a breathable atmospheres are terrible candidates for extraterrestrial life.
A long time. Voyager 1 is the fastest object that far away at 17km/s, at which rate it would take 493,775 years.

~ Amory (u • t • c) 15:34, 16 December 2009 (UTC)[reply]

The correct formula for the surface gravitational acceleration is Gm/r². Assuming a rocky planet with density simmilar to earth's density you get

g_Planet=g_earth(mass_Planet/mass_earth)^1/3

g_Planet=17m/s²

Dauto (talk) 16:37, 16 December 2009 (UTC)[reply]

Whoops, brainfart. Fixed, thanks. ~ Amory (u • t • c) 17:08, 16 December 2009 (UTC)[reply]

While Voyager is the fastest object made by man, it was not designed solely to travel as fast as possible. I would imagine that if cost was not much of an issue, we could, with current technology, create a much faster spacecraft, capable of at least 1% lightspeed and probably more. That would shorten the trip to the order of hundreds or thousands of years. Not great, but it beats half a million years. Googlemeister (talk) 16:05, 16 December 2009 (UTC)[reply]

Quibble: Not fastest. The Voyager 1 article says: The current speed of New Horizons is slightly greater than Voyager 1 but when New Horizons reaches the same distance from the sun as Voyager 1 is now, its speed will be about 13 km/s compared to Voyager's 17 km/s. Comet Tuttle (talk) 18:02, 16 December 2009 (UTC)[reply]

0.01c would be very difficult with current technology. I think the only technology we have that could do it is an ion drive and we are very much in the early days of ion drives. Rockets would require far too much reaction mass to get up to that kind of speed and would be completely infeasible. Laser propulsion would be a good way to do it, but I don't think anyone has even made a working prototype of such a system. --Tango (talk) 16:48, 16 December 2009 (UTC)[reply]

Probably. Best I could come up with back of the envelope is 0.5%c, and it would be quite the engineering feat to get 10,000 solid rocket boosters into orbit and lash them together so that you have 10 useful stages and a final craft weight of only 10,000 lbs. Also would not be that fun for any human since it would get up to speed in about 20 minutes and people can not pull 4 g (Correction, 4,000 g) for that long can they? Googlemeister (talk) 17:32, 16 December 2009 (UTC)[reply]

Also you'd rocket right past that exoplanet. More likely you'd want to burn half your fuel on the way there, then wait thousands of years, then on approach, your descendants would burn the other half to slow down and reach the exoplanet at a reasonable speed so they could enjoy the visit. Comet Tuttle (talk) 17:56, 16 December 2009 (UTC)[reply]

Is that 10,000lbs the payload mass or the initial mass of the whole craft? Either way, I don't think it's possible. The Apollo mission payloads were about 100,000lbs, I think, and they were only supposed to keep 3 people alive for about a week. A generation ship (which we seem to be talking about) would need at least 50 people and they would need to kept alive (and sane) for hundreds of years, which would require a much greater payload. If you use more realistic estimates of the payload mass you'll find the amount of rocket fuel required would be completely infeasible, even if you could overcome the engineering problems. --Tango (talk) 18:23, 16 December 2009 (UTC)[reply]

Aside from anything else - the news of these new exo-planets only appeared a few days ago. Wikipedia is an encyclopedia - not a newspaper - and while we often do create articles as the news breaks - there is no particular guarantee that this will happen for any given story. That said:

It's tempting to suggest (as others have) that at 5 times the mass of earth, the gravity would be 5 times as great - but gravity gets weaker as you get further from the center of gravity of the planet - so a planet that's 5x the mass of the earth that's made of something very dense (lead maybe) would be smaller than a planet of the same mass that's made of (say) aluminium. Hence the gravity on 'planet lead' would be greater than on 'planet aluminium'. So it's not just the mass - the density matters too. Without knowing both numbers, we have to make a kinda guesstimate that maybe the density of these new planets are similar to earth - and if that were the case, the gravity definitely wouldn't be 5x larger because the planet's diameter would be the cube-root of 5 times (1.72 times) larger. Since gravity drops off as the square of the diameter - we're looking at gravity that's 5/(1.72x1.72) = about 1.7 times more than here on earth. So if you weigh 150lbs here - you'll weigh 255lbs there...that's a lot - but soldiers walk around with 80lb packs on their backs and they seem to manage - so the gravity wouldn't stop you from living there - but it would make life uncomfortable. However, you wouldn't want to have to wear a massive spacesuit or anything like that. But this depends on the density of the planet. If it's lower density than earth, the gravity could easily be earth-normal. If it's even slightly denser than earth - we're in deep trouble!

Free oxygen is unlikely to exist there unless there is active plant life or something somewhat similar. Oxygen is a fairly reactive element and will combine with all sorts of materials in the soil and would probably eventually disappear unless continually renewed somehow. It's possible this happened on Mars where the reaction of oxygen with iron in the soil created the red color...rust. So it's likely that without life, there would be no free oxygen. However, there might be CO2 or water vapor - and you could maybe carry some kind of battery-powered gizmo that would convert CO2 or water vapor to oxygen and thereby survive so long as you have power. Also, we could maybe seed the atmosphere and soil with plant life before we go there (See terraforming) so that there would be a nice oxygenated atmosphere ready by the time we got there. This has been proposed for Mars. So we could use Mars for practice and maybe we could colonize these planets later.

SteveBaker (talk) 17:34, 16 December 2009 (UTC)[reply]

It is very difficult to say what kind of terraforming would be required. Different planets differ from Earth in different ways. For Mars, we need to warm it up and massively increase the atmospheric pressure. For Venus, we need to do the exact opposite. For this newly discovered planet, who knows? Creating the oxygen is probably the easy bit (as you say, we just need to seed the planet with plants), it will be adjusting the pressure and temperature that is hard. As long as the terraforming can be done without people being present, then there is a factor in our favour - unmanned terraforming probes could be sent much faster than the colonists, since the probes could survive much higher accelerations. That should mean that the colonists could arrive to find a nice habitable planet waiting for them having had hundreds of years for a balanced and reasonably diverse ecosystem to develop. --Tango (talk) 18:15, 16 December 2009 (UTC)[reply]

"vascular" headaches

Why is vascular headache an outdated term? The page implies that no headaches are now thought to be related to blood vessel swelling. This is at odds with the page for cluster headache which says "The intense pain is caused by the dilation of blood vessels". 81.131.54.224 (talk) 16:08, 16 December 2009 (UTC)[reply]

The article has no sources and the "outdated" edit was made by an IP with no explanation, so the reason for it is not entirely clear. My understanding based on a quick scan of the literature is that (1) "vascular headache" is no longer an officially recognized diagnosis; (2) the theory that migraine is caused by vascular changes has been called into question; however (3) there is no doubt that some headaches are caused by vascular effects; and (4) the term "vascular headache" is still pretty widely used. Looie496 (talk) 17:53, 16 December 2009 (UTC)[reply]

OK, I'm going to insert your (3) into the article. 213.122.38.14 (talk) 19:31, 16 December 2009 (UTC)[reply]

Don't forget about temporal arteritis -- can lead to blindness. DRosenbach ^{(Talk | Contribs)} 02:53, 17 December 2009 (UTC)[reply]

p-phenylenediamine

does p-phenylenediamine degrade when exposed to air and/or light? if so how much? —Preceding unsigned comment added by 74.65.3.30 (talk) 18:30, 16 December 2009 (UTC)[reply]

Oh yes it does. It goes black! Just like most aromatic amines - air oxidation, a bottle of aniline will be a brown liquid - it's colourless when distilled, as soon as air gets in it starts to turn yellow. The phenylenesiamines are even easier oxidised, which is why derivatives of them are used as developing agents in photography - see C-41 process. Ronhjones ^(Talk) 22:27, 16 December 2009 (UTC)[reply]

CHARGED BLACK HOLES

Hello,

I read and come to know that black holes do have charged and react to external charge, but how not known to me. Can you tell me please. —Preceding unsigned comment added by Harshagg (talk • contribs) 19:03, 16 December 2009 (UTC)[reply]

If you drop something with an electric charge into a black hole - the hole retains that charge...or if something with an electrical charge collapsed to form a black hole - then it could happen that way too. Of course there is the practical question of what we could imagine that was large enough - and charged enough to do that - so the idea of electrically charged black holes is still kinda theoretical. I don't think anyone is seriously saying that we have any reason to suspect they are out there to be found. SteveBaker (talk) 19:08, 16 December 2009 (UTC)[reply]

Steve, the honest answer is that we don't know whether any blackholes out there actually have a non-neglible charge. But I find it perfectly believable that they might have a small but non-negligible net charge. Dauto (talk) 19:47, 16 December 2009 (UTC)[reply]

The problem with black holes having a charge is that, if they can have a small charge, they should be able to have a large charge. Highly charged back holes have naked singularities (see Reissner–Nordström metric). Apparently there is something to do with supersymmetry that fixes this problem (by making higher charged block holes impossible), but I've never really understood supersymmetry. --Tango (talk) 20:36, 16 December 2009 (UTC)[reply]

Somebody asked this before, but I'm not sure I find the answer fully satisfying: Since electrical charge is communicated via photons, how can we detect that the hole is charged? If I drop, say, 10e30 naked protons into the hole, how can I detect this charge? --Stephan Schulz (talk) 20:27, 16 December 2009 (UTC)[reply]

You ask how can you detect the charge of the protons. The answer is 'The same way you can detect the mass of the protons'. The electric charge of the protons don't get destroyed by the blackhole. it becomes part of the blackhole. Dauto (talk) 02:15, 17 December 2009 (UTC)[reply]

Ok, so how to do we detect the mass of the protons? If nothing can escape the event horizon, that includes photons and gravitons. My understanding is that the (virtual) photons or gravitons are created at, or just outside, the event horizon, rather than inside it, but I'm not entirely convinced about how that works. --Tango (talk) 03:24, 17 December 2009 (UTC)[reply]

The event horizon is determined by the condition that the escape velocity becomes the speed of light. Coulomb interaction is mediated by only virtual photons, whose effective speed is not anyhow limited (their propagator is not zero over space-like intervals). So I see no immediate contradiction in probing the electrostatic charge of a black hole. If the charge distribution inside the event horizon were changing, then we (the outsiders) would receive no information on that, as that would be conveyed by electromagnetic waves, i. e. real photons, which surely cannot escape. It would still need some computation (applying quantum field theory in curved spacetime) to prove the relevant part of the "No hair theorem" that the total charge of a black hole is observable, but the charge distribution is absolutely not.—Pt_(T) 06:24, 17 December 2009 (UTC)[reply]

Here is another question. We know that gravity is a weak force, compared to the electrostatic force. So it is conceivable that I have a black hole which is charged to a degree that the electrostatic repulsion is larger than the gravitational attraction. Does that mean that the black hole will start bleeding protons? In fact, does this mean that the even horizon is at different radii for negatively charged, positively charged, and neutral particle? The net force (sum of gravity and electrostatic) is certainly different for each... --Stephan Schulz (talk) 08:16, 17 December 2009 (UTC)[reply]

there is a limit to how charged a black hole can be. the charge to mass ratio is actually way below that of a proton. The reason would be that to push all those positive protons together takes a lot of energy. Somewhere someone here worked out the energy to get a mole of protons in a particular apace. Graeme Bartlett (talk) 09:46, 17 December 2009 (UTC)[reply]

Well, since both gravity and electrostatic force follow inverse-square laws, I should be able to drop protons into a black hole until mass and charge exactly balance out. In that state, the black hole would exert no net force on a proton (but, of course, a lot of force on neutral matter, and an even bigger one on negatively charged particles). --Stephan Schulz (talk) 13:12, 17 December 2009 (UTC)[reply]

Strong gravity is not inverse-square anymore, see Kepler problem in general relativity#Relation to classical mechanics and precession of elliptical orbits: there is an inverse-cube term in the effective potential or, equivalently, a r^-4 term in the force law. In addition, curvature of spacetime modifies the Maxwell's equations including the Gauss's law, which would otherwise give the inverse-square behaviour of electrostatic force. I haven't calculated if things actually still happen to cancel and your idea works, but I doubt it.—Pt_(T) 14:49, 17 December 2009 (UTC)[reply]

If you interpret gravity as a deformation of spacetime, rather than a force, then it becomes clear that it can't be cancelled out. No matter how strong an electromagnetic field is, it can't make a charged massive particle move along a space-like path and that is required to leave an event horizon. --Tango (talk) 15:52, 17 December 2009 (UTC)[reply]

In order for the particle to leave the event horizon it could also move backwards along a time-like path which is also impossible. Dauto (talk) 02:04, 18 December 2009 (UTC)[reply]

As I mentioned above, if the charge to mass ratio gets too great (I think the charge being greater than the mass in the usual dimensionless units) then you end up with a naked singularity, which is usually interpreted as meaning it can't happen. --Tango (talk) 15:52, 17 December 2009 (UTC)[reply]

how far we go back things become less accurate?

Do we 100% know where the continents were 300 million years ago or is this just a theory. Because The Future is Wild said Antartica was in the equator 300 million years ago, most show Artartica was in SP at that time. Is this right the further we go back in historical time, the less we know. Do we absolutely know if southern Africa was 75 degs. south 200 million years ago, some model shows southern Africa only 55 degs south at that time.--209.129.85.4 (talk) 22:17, 16 December 2009 (UTC)[reply]

We don't 100% know much of anything, when you get down to it, especially something like where the continents were 300 million years ago. We have estimates and projections and simulations and assumptions that probably put us in the right ballpark, but then again, they might be wrong in some major way that we don't know at the moment. I would probably suggest that the issue is not "the less we know" but "the more uncertain our knowledge becomes" the further backwards we extrapolate, but that isn't universally applicable. --Mr.98 (talk) 23:20, 16 December 2009 (UTC)[reply]

The margins of error on things like the positions of tectonic plates do get bigger as we go further back, that is correct, however the error is pretty small. I think there is some disagreement on the details of what happened before Pangea formed, but after that is all seems pretty clear. We have a good discussion of the history of Antartica here. I think 300 million years ago is recent enough that we are fairly sure about it. Africa and Antarctica were both part of the supercontinent of Gondwana 200 million years ago, so they would have been quite close together. About 500 million years ago, Antartica was somewhere near the equator, it moved to the South Pole by around 360 million years ago. I'm not sure what The Future is Wild said, but either you have misunderstood it or they have made mistake - it's probably just a mistake about the time, it's 500 million years ago, not 300. --Tango (talk) 23:33, 16 December 2009 (UTC)[reply]

That said for Antartica to be green again like it was 300 million years ago. No mistakes--209.129.85.4 (talk) 19:24, 17 December 2009 (UTC)[reply]

This didn't say anything about the past, they just said Antartica would be green and hot, and it will be back on equator in 100 million years. I doubt if our article made a mistake on time about Tropical Antarctica.--209.129.85.4 (talk) 19:41, 17 December 2009 (UTC)[reply]

The best information has come from core samples taken by drilling into oceanic plate and examining magnetic alignment. However, oceanic plate is constantly being newly created and the older plate destroyed by the very process that causes continental drift. The further back one goes, the less plate of that age there is still in existence. Past the Mesozoic it is all gone and the information becomes much more sketchy. SpinningSpark 11:45, 17 December 2009 (UTC)[reply]

ICP-Chapter 11 Review-Motion

Please help me with these questions. I'm studying for finals and need to know the answers to these questions.

46 questions

FILL IN THE BLANK

1. The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant ____________?

2. The motion of an object looks different to observers in different ____________?

3. Speed is measured in units of _____________?

4. A moving object does not _______________ if its velocity remains constant?

5. The acceleration of a moving object is calculated by the deviding changes in _____________ by the time over which the change occurs.

6. Two or more velocities add by _____________?

7. The direction and length of a straight line from the starting point to the ending point of an object's motion is _______________?

8. Displacement and velocity are examples of _____________ because they have both magnitude and direction.

9. s=d/t is the equation that defines _______________?

10. The difference between speed and velocity is that velocity indicates the ______________ of motion and speed does not.

11. Because its _____________ is always changing, an object moving in a circular past experiences a constant change in velocity.

12. The SI unit for measuring _________________ is the meter.

13. Accelerated motion is represented by a(an) ___________________ line on a distance-time graph.

14. A constant slope on a distance-time graph indicates ____________ speed.

15. A cars speedometer measures _______________.

16. A car that increases its speed from 20 km/h to 100 km/h undergoes ________________ acceleration.

17. The sum of two or more vectors is called the ____________.

18. A distance-time graph indicates an object moves 20 km in 2 h. The average speed of the object is _____________ km/h.

SHORT ANSWER

19. In the equation for acceleration, a=v/t, how can you describe acceleration if the numerator is negative?

20. Vector addition allows you to add what two quantities for any number of vectors?

21. Distance is a measure of length. What information does displacement give in addition to distance?

22. What types of changes in motion cause acceleration.

23. What is the SI unit best suited for measuring the height of a building?

24. What information does the slope of a speed-time graph provide?

25. a=v/t is the equation for calculating the acceleration of an object. Write out the relationship shown in the equation using words.

26. Bus A travels 300 m in 12 s. Bus B travels 200 m in 12 s. Both vehicles travel at a constant speed. How do the distance-time graphs for these two speeds differ?

27. A child rolls a ball 4 m across a room. The ball hits the wall and rolls halfway back toward the child. Using vector addition, calculate the balls displacement.

28. How is motion described when the velocity of an object changes by the same amount each second?

29. What is the significance of the slope in a distance-time graph?

PROBLEM

32. If you ride your bike at an average speed of 2 km/hr and need to travel a total distance of 20 km, how long will it take you to reach your distance?

33. During a race, a runner runs at a speed of 6 m/s. Four seconds later, she is running at a speed of 10 m/s. What is the runner's acceleration?

34. Explain how velocity is different from speed?

35. Picture a ball traveling at a constant speed around the inside of a circular structure. Is the ball accelerating?

36. A girl walks from her home to a friend's home 3 blocks north. She then walks east 2 blocks to the post office, 1 block north to the library, and 1 block east to the park. From the park, she walks two blocks west to the movie theater. After the movie, she walks 4 blocks south to the pet store. What is the girls displacement from her starting point to the pet store? Where is the location of the pet store in relation to her home? Calculate the distance she walked in blocks.

MULTIPLE CHOICE

1. Instantaneous speed is measured

A) over a very tiny "instant" of time B) at the starting point C) when the object reaches its destination D) over the duration of the trip

2. The slope of a line on a distance-time graph is

A) displacement B) time C) speed D) distance

3. A person drives three blocks north, then turns east and drives 3 blocks. The driver then turns south and drives 3 blocks. How could the driver have made the distance shorter while maintaining the same displacement?

A) by driving north 1 block and east 4 blocks B) by driving back to the starting point by the same route C) by driving east 3 blocks by the starting point D) by driving west 3 blocks from the starting point

4. Which example identifies a change in motion that produces acceleration?

A) a ball moving at a constant speed around a circular track B) a particle moving in a vacuum at a constant velocity C) a vehicle moving down the street at a steady speed D) a speed skater moving at a constant speed on a straight track

5. A car traveling 88 km in 1 hour, 90 km in the next 2 hours, and then 76 km in 1 hour before reaching its destination. What was the car's average speed?

A) 209 km/h B) 63.5 km/h C) 74.5 km/h D) 254 km/h

6. Suppose you increase your walking speed from 1 m/s to 3 m/s in a period of 2 s. What is your acceleration?

A) 6 m/s squared B) 1 m/s squared C) 2 m/s squared D) 4 m/s squared

7. The slope of a speed-time graph indicates

A) acceleration B) direction C) speed D) velocity

8. Speed is the ratio of the distance of an object moves to

A) the motion of an object B) the direction the object moves C) the displacement of the object D) the amount of time needed to travel the distance

9. A ball is rolled uphill a distance of 3 meters before is slows, stops, and begins to roll back. The ball rolls downhill 6 meters before coming to a rest against a tree. What is the magnitude of the ball's displacement?

A) 9 meters B) 6 meters C) 18 meters D) 3 meters

10. The rate at which velocity changes is called

A) acceleration B) motion C) speed

D) vectors

Please please please answer the ones you know(: please and thankyou! you will be of big help to do so. —Preceding unsigned comment added by Kaimorgan16 (talk • contribs) 23:01, 16 December 2009 (UTC)[reply]

The standard disclaimer:

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.

applies here. Key phrase "Please attempt to solve the problem yourself first." You'll get better responses if you make some effort to tell us why you're having answering the questions on your own. -- 128.104.112.87 (talk) 23:05, 16 December 2009 (UTC)[reply]

I hid the myriad questions, since we won't be answering them in that form. --Tardis (talk) 23:08, 16 December 2009 (UTC)[reply]

That is far too many questions. You need to actually try and answer them yourself and come back with those ones that you really are stuck on. Try looking up the topics in Wikipedia. For example, question 3 is answered in our article on speed (there is a whole section on it). --Tango (talk) 23:11, 16 December 2009 (UTC)[reply]

Quoth the teacher "Distance is a measure of length" ??? -- Finlay McWalter • Talk 23:49, 16 December 2009 (UTC)[reply]

I'm curious as to what age this would be for. And, the answers are simple and basic - the student not knowing the answers implies that they have not attended class or at least been ignoring the teaching. Wikipedians should not encourage this behaviour by answering the questions. 78.149.247.13 (talk) 10:36, 17 December 2009 (UTC)[reply]

ANNs

There is a very good Excel spreadsheet example of the Perceptron method in the article but the subtitles are incomplete and need additional entries which I plan to remedy shortly. Does anyone know where I can find a similar Excel spreadsheet example of an XOR capable layered ANN and one that displays all of the computations for Backpropogation? 71.100.0.206 (talk) 23:17, 16 December 2009 (UTC) [reply]

ANNs in Excel is easily found via google. This one for instance: [22] I'm guessing that this one could be easily modified to show the underlying computations. EverGreg (talk) 08:35, 17 December 2009 (UTC)[reply]

VBA is easy to find, especially those with a price tag. I'm not looking for a VBA applications program but only an example with the computations for each column at the top as in the Perceptron example. 71.100.0.206 (talk) 17:02, 17 December 2009 (UTC) [reply]

I'd be interested in finding something similar for a radial-basis function, and other AI algorithms. Unfortunately I do not understand or use C. 78.149.247.13 (talk) 11:21, 17 December 2009 (UTC)[reply]

December 17

testicular torsion

what happen if the dead testicle is not removed post testicular torsion? —Preceding unsigned comment added by Reolmadrid (talk • contribs) 03:26, 17 December 2009 (UTC)[reply]

See the "Treatment" section of our testicular torsion article. DMacks (talk) 04:34, 17 December 2009 (UTC)[reply]

Explain why cancer has a genetic code?

Please explain how cancer has a genetic code, accoding to this http://news.bbc.co.uk/1/hi/health/8414124.stm I thought cancer was just the result of unlucky mutations caused by bad environmental things (like smoking, too much sun, sodium nitrate etc). I thought only a proper species would have a distinctive genetic code. 78.149.247.13 (talk) 10:46, 17 December 2009 (UTC)[reply]

I believe you are right about mutations causing cancer; if I'm reading the article correctly, it seems that they're just recording what those mutations are. The mutations are changes to the ~~genetic code~~ genome so the cancer cells do have a different ~~code~~ genome from the healthy cells, but it's not the necessarily the same for ever cancer cell as they are mostly random changes. I believe the hope is that by recording these they can gain insight into which mutations will cause cancer, so the oncogenes I guess. I haven't studied genetics too much so my answer is probably lacking in some way. J kasd 11:33, 17 December 2009 (UTC)[reply]

We have an article on this, gene expression profiling in cancer, and see also oncogenomics. Note also, that a predisposition to some cancers can be hereditary (covered in the cancer article) and so these too, can be detected by looking for the genetic marker. SpinningSpark 12:17, 17 December 2009 (UTC)[reply]

One more article you may want to read is tumor suppressor gene. SpinningSpark 12:22, 17 December 2009 (UTC)[reply]

Your confusion is caused by an unfortunate oversimplification made by the journalist who wrote the article, not the scientists who carried out the research. If you read the article on genetic code, it explains that the "code" is the set of rules used by the cell to translate the instructions encoded in the DNA into the proteins that actually do the work in the cell. The "genetic code" is basically the same among all species, with some rare "variants" described in certain single-celled organisms. This is different than the genome -- the entirety of all the genetic information in a cell -- which differs between individuals, and which can accumulate mutations in different cells throughout the life of the organism. Mutations aren't changes to the "genetic code" but changes in the genome. The article title (and the answer by Jkasd) confuses the distinction between the "code" (which is invariant) and the "genome" (which can be highly variable). Cancer cells still follow the same "rules" when translating the genetic information. They just accumulate mutations that activate certain genes (see oncogene) or inactivate other genes (see tumor suppressor gene). Not surprisingly, they also accumulate a lot of mutations that probably have no effect at all. What many cancer biologists are doing these days is to examine "cancer genomes" to generate catalogs of all the mutations found in individual tumor samples, then to see whether the same mutations keep coming up over and over again in different people. This would give us additional insight into the mechanisms of carcinogenesis, and hopefully point towards effective treatments. --- Medical geneticist (talk) 13:27, 17 December 2009 (UTC)[reply]

computer CD ? DVD

what is the material of construction of CD & DVD ? what is the difference ( Construction) between CD & DVD ?193.188.60.123 (talk) 11:10, 17 December 2009 (UTC)[reply]

According to our article CD, they are mostly made of polycarbonate plastic with a thin layer of aluminum. I believe that DVDs are made of the same materials, the difference being the size of the pits and the format used. See Optical Disc for more general information. J kasd 11:24, 17 December 2009 (UTC)[reply]

A big difference between CDs and DVDs that you can easily notice if comparing the two from the side is that in DVDs the reflective layer is in the middle i.e. there are two layers of plastics on the top and bottom. This is because the amount of information that can be stored depends how close the data layer is to the surface so by reducing the thickness of the protective layer they can increase the amount of information that can be stored. There's some explaination here [23] for example (related to Blurays where the data layer is even closer to the surface). Of course to keep the thickness the same as CDs, they add another protective plastic layer to the top. This also means that the reflective surface is protected from scratches unlike with CDs where it can be scratched (and if it is, you're basically screwed). It also means double sided DVDs are possible (albeit still fairly rare because people don't like switching sides) whereas with CDs they're not compliant with the spec. As I mentioned, this is usually easy to see if you look closely from the side and you can actually differentiate DVDs from CDs in a spindle (useful for example if you have a spindle and you're looking for a specific CD or DVD in a mix or you think you misplace it). Some DVDs particularly recordable ones don't bother to put any coating at the top (or it may not cover the whole top) so you can clearly see the reflective layer is underneath from the top side as well.

Of course DVDs can also be dual layer. This means there are actually two data layers each with a reflective metal layer (one being semi transparent) and a small protective layer in between. See [24] [25] for example (these are recordable but much of the same applies to pressed DVDs.) However they are close enough together that it can be difficult to see from the side. From the bottom however if you look at the spindle you should see two different rings perhaps with a different barcode and maybe even a different description (e.g. L0 and L1). One is for each layer.

Also when it comes to recordable DVDs you they use different dyes from CDs.

BTW because of the different track pitch you also get different diffraction grating patterns in particular, the spacing between the lines is wider with a DVD. This works best with a laser e.g. [26] [27] but as with anything involving lasers please take great care when trying that and make sure you know what you're doing. If you don't, you should be able to see this with an ordinary light although probably not well enough to accurately measure. From memory a small light works well, particularly if it has two or three peaks. For example, I had a mobile phone with a fairly long but narrow LED on top (you can see the LED in this photo, it's the transparent bit between the self potrait reflective button thing and the camera) that could shine different colours, it was interesting to see the different colours that made up these and it was also a good way to compare the diffraction patterns of CDs and DVDs.

Nil Einne (talk) 14:51, 17 December 2009 (UTC)[reply]

Particles And Black Holes, are They the Same Thing?

If a particle has mass, but is a zero dimensional point according to standard model doesn't that mean it has an infinite density meaning it is a black hole? I know that according to some theories like m theory, black holes and particles are remarkably similar,but if a particle has infinite density doesn't that make it a black hole. Black hole evaporate by releasing Hawking radiation, but no one knows for sure wether they completely evaporate into a burst of gamma rays after becoming a micro black whole or wether they reach some stable state and the process stops. If at some point black holes do become stable, could a particle actually just be its stable form? —Preceding unsigned comment added by 74.67.89.61 (talk) 12:20, 17 December 2009 (UTC)[reply]

Those are some interesting questions. Our article on the black hole electron briefly touches on some of these points, including the issue of stability of such (hypothetical) particles. The answer to your final question boils down to, "Yes, that would be compatible with some models of physics." Unfortunately, we don't have now (and may never) have the tools necessary to probe the structure of matter on small enough scales to confirm or refute the presence of tiny black holes inside each 'fundamental' particle. TenOfAllTrades(talk) 13:48, 17 December 2009 (UTC)[reply]

Why does once in a blue moon = 1.16699016 × 10^(-8) hertz?

Says Google.

Why?--72.178.133.37 (talk) 14:04, 17 December 2009 (UTC)[reply]

Because a blue moon occurs on average every 2.7154 years and a year has 365.256363051*86400 seconds. Thus, a blue moon occurs every 2.7154*86400*365.256363051 seconds, or with a freqency of 1/85692999.878958419s or 1.1669564625027745e-08Hz (minor rounding errors may have occurred). --Stephan Schulz (talk) 14:18, 17 December 2009 (UTC)[reply]

I don't understand the hertz though. The article says that the unit is defined as "cycles per second". What is a cycle? I've never heard of that unit.--72.178.133.37 (talk) 14:21, 17 December 2009 (UTC)[reply]

From wikt:cycle - "An interval of space or time in which one set of events or phenomena is completed." --LarryMac | Talk 14:25, 17 December 2009 (UTC)[reply]

So how do you compare frequencies? Because when I think of frequencies, I think of radios (sound), radiation (light), and so forth. They all use hertz? Isn't that a bit impractical? I've never heard of, say, the frequency of some light being described in hertz (or megahertz or any size prefix).--72.178.133.37 (talk) 14:39, 17 December 2009 (UTC)[reply]

You compare them (I'm not really sure what you mean by "how" there). Our hertz article notes, though, that "for historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies". For known speed (in this case, c), frequency and wavelength can be trivially converted, so it's simply a matter of nomenclature. Visible light, for what it's worth, is in the hundreds of terahertz range. — Lomn 14:47, 17 December 2009 (UTC)[reply]
Yes. Hertz is just another name for "1 per second" or 1/s. 440 Hz is the frequency of a sound in concert pitch A. That's 440 "cycles" or "vibrations" of the air going back and forth in one second. Around 100 MHz in the electromagnetic spectrum is FM radio. 550 THz EM is green light. --Stephan Schulz (talk) 14:49, 17 December 2009 (UTC)[reply]
(EC) For completeness: You can transform one into the other through v=lambda * f ([phase]speed = wavelength times frequency). For EM-radiation, the speed is fixed at lightspeed. And the reason why different things (sound, radiation, all things that rotate on an axle) are all described using hertz is that they all are, on some level, the same: A circular process which repeats, so you can count how often it repeats in one second, giving you the hertz value. --TheMaster17 (talk) 15:01, 17 December 2009 (UTC)[reply]

So basically then, you can convert anything that happens every once in a while to hertz? So you can say something like, "my birthday is 3.16887646 * 10^(-8) hertz". Doesn't this get confusing?--72.178.133.37 (talk) 15:02, 17 December 2009 (UTC)[reply]

You can, and yes, it's often completely impractical (as is the Google example that started this). However, odd units and transformations can be useful teaching tools -- you may want to look at the firkin-furlong-fortnight unit system, a system of measurement that exists for little purpose except geek humor. — Lomn 15:08, 17 December 2009 (UTC)[reply]

Although as a somewhat-pedantic note, "every once in a while" is subject to interpretation. Hertz values are most commonly used for things that cycle regularly, without significant variation. Expressing the "hertz of New York Yankees championships" wouldn't have much meaning, because the time between each is variable and not dependent on the other values. Google's use of "blue moon" is something of a middle ground -- the true time between blue moons is variable (thus the value they give in hertz is an approximation), but it's also predictable. — Lomn 15:13, 17 December 2009 (UTC)[reply]

In fact, there are two SI units that are both "1 per second" or 1/s. The hertz is intended for regularly repeating events, like the frequency of a wave, while the becquerel is for radioactive decays, which occur randomly but whose expected rate is predictable. --Anonymous, 21:57 UTC, December 17, 2009.

I'm reminded of this [[28]]. Truthforitsownsake (talk) 00:36, 18 December 2009 (UTC)[reply]

Wormholes and Blackholes

What is the difference between wormholes and blackholes? --Reticuli88 (talk) 14:55, 17 December 2009 (UTC)[reply]

Wormhole v. Black hole. First sentence of each should clear it up. --Mr.98 (talk) 15:10, 17 December 2009 (UTC)[reply]

If I had a choice, I'd prefer to go thorough a wormhole then a black hole. At least I think so. Obviously once I get thorough the wormhole and find some aliens with anal probes I reserve the right to change my mind Nil Einne (talk) 17:08, 17 December 2009 (UTC)[reply]

Well, it is not even theoretically possible to go "through" a black hole. Think well instead of tunnel. Googlemeister (talk) 17:12, 17 December 2009 (UTC)[reply]

Was wondering how long it would be before someone said something like that Nil Einne (talk) 18:42, 17 December 2009 (UTC)[reply]

Collective Human Mind Connection to the planets Ecosystem

Awhile back I remember reading a wikipage on some Theory on the entire human population mind(s) being connected on some unnamed level with the Earths Ecosystem. Does anyone recall what this Theory is called? Cheers, --i am the kwisatz haderach (talk) 17:09, 17 December 2009 (UTC)[reply]

Sounds a bit like James Lovelock's Gaia theory. --TammyMoet (talk) 17:15, 17 December 2009 (UTC)[reply]

Specifically, his Gaia hypothesis.--Shantavira|^{feed me} 17:17, 17 December 2009 (UTC)[reply]

That was it. Thanks much. --i am the kwisatz haderach (talk) 17:24, 17 December 2009 (UTC)[reply]

Sorry, but I beg to differ. While science-fictional extensions to it might have been made, Lovelock's Gaia hypothesis itself does not assume any supposed human group mind, it merely posits that the Earth either behaves somewhat 'like' a single living organism due to biosphere-atmosphere-hydrosphere-lithosphere interactions (the 'weak' form), or that by the usual definitions of life, it 'is' a living organism (the 'strong' form). —Preceding unsigned comment added by 87.81.230.195 (talk) 16:36, 18 December 2009 (UTC)[reply]

Is a hot radiator disrupting my TV's remote control?

I have a tv near to and somewhat facing a hot radiator. Could this be disrupting the infra-red signal from the remote control? The standby light sometimes starts flashing and the tv won't start - I'm wondering if this might be the cause. Thanks. 84.13.35.30 (talk) 18:00, 17 December 2009 (UTC)[reply]

It's very unlikely. Infrared diodes usually send signals modulated by a digital code, so it would be difficult for a steady IR source (even if it radiates at the same wavelength) to interfere. If the emitted IR signal from the radiator is very strong, it might be plausible that it's saturating the receiver diode's front end amplifier, but this again seems unlikely. Nimur (talk) 18:06, 17 December 2009 (UTC)[reply]

Extremely unlikely. The IR used by a TV remote is about 900nm, which is only emitted (as thermal radiation) in considerable quantities by something over maybe 500°C (900nm is only slightly longer than the 700-750nm limit of the visible spectrum, so it needs to be almost red hot). Your radiator won't be anywhere near that hot. An incandescent light bulb will emit far more at that wavelength than your radiator ever could, and TV remotes work fine in rooms light by incandescent bulbs. --Tango (talk) 19:01, 17 December 2009 (UTC)[reply]

I propose an experiment. You may be interested to know that you can use the camera in your cellphone (assuming you have one) to actually SEE the infrared light coming out of the TV remote. Cheap cellphone cameras don't have infrared filters - so they see IR light at the frequencies that TV remotes use. Most buttons on the TV remote send a brief flash - but if you hold down the volume up or down button, you should get either a solid light or a fast flashing light. This lets you be sure that the batteries aren't dead (or put in backwards or something). Now - you can sit with your camera where the TV's sensor is (do it at night with the room lights off) and you'll be able too see if there is something else interfering with the signal. What you WON'T see is the radiator glowing because of the heat! But maybe there are confusing reflections bouncing off the shiney paint on the radiator? You'll see what the TV's sensor sees - which is really kinda cool! SteveBaker (talk) 01:16, 18 December 2009 (UTC)[reply]

I do not have a cellphone, but the remote has a visible light that flashes when I press a button, so I assume its working. 89.243.91.31 (talk) 21:02, 18 December 2009 (UTC)[reply]

silicone or rubber compound used for grips etc...

I am working on a new fly fishing tool that requires a very soft rubber grip (possibly translucent) I have only seen it on a hairbrush handle and nothing else. It like nothing I have ever seen before. Doeas anyone know what type of material this is or what it is called.? It is somewhat clear,very soft , no memory any help would be appreciated greatly thanks Jason ,pennsylvania —Preceding unsigned comment added by 24.229.199.70 (talk) 18:09, 17 December 2009 (UTC)[reply]

It's going to be hard to tell - but if I had to guess: Gel pads are usually made of a Polyurethane-based elastomer...these grips sound kinda similar to a gel pad. SteveBaker (talk) 19:52, 17 December 2009 (UTC)[reply]

following migration routes leading to discovery

Now-a-days hunters still wait along migration routes waiting for the opportunity to kill. Before the gun this was possibly done with bow and arrow or snares where flock were know to land. Even crocs take advantage of the knowledge of migration. Is it possible that the discovery of Greenland came form the following of the Barnicle Goose from Western Europe to Greenland over time of seeing it fly in that direction far out at sea? 71.100.0.206 (talk) 19:54, 17 December 2009 (UTC) [reply]

The discovery of Greenland by whom? Greenland has been settled by various people at various times. The Saqqaq culture settled Greenland in about 2500 BC, and left no written history; near as I can tell, it is unknown why they ended up there, or even where they came from. The European settling of Greenland came in the 10th century by way of the Vikings, doing pretty much what Vikings always did, which is to ride around in boats and find stuff to take. I don't think that there is any evidence that the Viking settlement of Greenland was as a result of following bird migrations. --Jayron32 20:11, 17 December 2009 (UTC)[reply]

Isn't there still controversy over who discovered America or has that been resolved?. American Indians were living on the continent long before Europeans arrived. ... of course I mean by Europeans. 71.100.0.206 (talk) 20:35, 17 December 2009 (UTC) [reply]

There's a notion sometimes called the Columbus principle, which states that it's not who discovers something first that counts, but who discovers it last. It's counterintuitive at first blush, but if you think about it, it's actually fair. If you discover something, but then don't succeed in causing knowledge of it to be preserved, what did you accomplish in the long run?

This is orthogonal to the point about the Americas already being inhabited at the time. From their point of view, of course none of the European explorers "discovered" anything; they already knew about it. But there was no way for that knowledge to be transmitted to Europe, so from the European point of view, it was a genuine discovery. There is no contradiction between these two things. --Trovatore (talk) 23:55, 17 December 2009 (UTC)[reply]

I happen to be reading The Route To India, A Journal Of The First Voyage Of Vasco De Gama in 1497-9, written at the time, and it is very clear from that that when going around the east coast of Africa, rather than sailing along a dark continent, the area was in fact busy and vibrant with Arab and Indian traders who had already been to India and to the Mediteranean as well. When they reached India, the explorers were surprised that the first person to come on board their ship could speak fluent Portugese. They also met an unnamed trader from Tunis who spoke european languages, so he was an earlier explorer than they were. 89.241.43.33 (talk) 12:20, 18 December 2009 (UTC)[reply]

In that regard now that I think about it I suppose a discovery of Greenland from trying to figure out where Barnacle Geese were headed if not put in a journal or made part of a story or persevered in some other way would then kill the discovery and the reason for it. Perhaps such a story has been overlooked if in fact it was preserved and what needs to be done now is to find it. 71.100.0.206 (talk) 00:27, 18 December 2009 (UTC) [reply]

We already have such a story: how Gunnbjörn Ulfsson was blown off course and spotted some islands. See History of Greenland, Saga of the Greenlanders and Erik the Red's Saga. 75.41.110.200 (talk) 02:08, 18 December 2009 (UTC)[reply]

You know, I'm guessing here but if I were a bird flying to Greenland from Western Europe and I flew over Iceland, that is where I might stop to have a few veggies and a good night's rest. 71.100.0.206 (talk) 04:31, 18 December 2009 (UTC) [reply]

Greenland was discovered after Iceland. In fact, Iceland was already settled to some extant. Googlemeister (talk) 14:44, 18 December 2009 (UTC)[reply]

Ice in My Freezer "Sublimates". Why?

If I make ice-cubes in the freezer on my refrigerator, the water becomes ice well enough, but after about a months time, I'm only left with slivers of ice at the bottom of the tray. I don't know if the ice is necessarily "sublimating" as I doubt that I'm getting steam in my freezer, but might the ice be going directly to water vapor? If so, why? All other freezers I've had required de-icing while mine isn't capable of keeping ice. Zhatt 22:00, 17 December 2009 (UTC)[reply]

Hmm, hard to say. Did you recently move to a drier climate or something? As a practical matter, though, I can't see it as very important; month-old ice tastes terrible (assuming you have anything other than ice in your fridge), and you should throw it out anyway.

Just by the bye, the verb is usually sublime rather than sublimate. Sublimating is something you do with psychological impulses that you can't ~~admit to yourself~~ oops, I think I got that wrong -- that's repression. You repress desires you can't admit; you sublimate the ones you can't satisfy. Or something like that.. --Trovatore (talk) 22:06, 17 December 2009 (UTC)[reply]

I don't know if it is technically sublimating, but it could be melting and then evaporating. Do you have a thermometer in your freezer (or can you put one there)? You may find it isn't really cold enough. If it is only just below 0°C then it will be very close to the triple point of water. That means water can very easily change between all three common states of matter. The water is always in a dynamic equilibrium, meaning there is always some bits melting, some bits freezing, some bits evaporating and some bits condensing. There should be the same amounts doing each so the total amounts of ice, liquid water and water vapour should stay the same but since your freezer doesn't ice up that probably means it has some kind of dehumidifier, so the bits that evaporate disappear off so there isn't much water vapour there to condense. That means the equilibrium is broken and the water gradually disappears as more bits melt, then evaporate and then get sucked up by the dehumidifier (which will then condense the water and collect it somewhere where it can evaporate out into the air outside the fridge). If you can get the freezer colder, that should reduce the amount of evaporation going on. It should be at least -10°C, probably colder (I can't remember the exact guidelines). --Tango (talk) 22:18, 17 December 2009 (UTC)[reply]

You don't know if it's technically subliming. --Trovatore (talk) 22:35, 17 December 2009 (UTC)[reply]

Yeah... I should have taken the hint when I edit conflicted with you and corrected my spelling... --Tango (talk) 22:56, 17 December 2009 (UTC)[reply]

Actually Wiktionary seems to think they're both acceptable. Subliming is just what I've heard, and I do like that it's a different word from the psych one. --Trovatore (talk) 22:59, 17 December 2009 (UTC)[reply]

Never heard of the triple point, but that sounds like a likely situation. I'll grab a thermostat on the way home and check it out. I'll report back here if I find out anything. Zhatt 23:04, 17 December 2009 (UTC)[reply]

Commonly in the UK snow disappears with the temp well below freezing. I don't know why you should be adverse to labelling it sublimation.--BozMo talk 23:11, 17 December 2009 (UTC)[reply]

The noun is sublimation, the verb is sublime. --Trovatore (talk) 23:15, 17 December 2009 (UTC)[reply]

I wonder if this could be a pondial thing, like orient/orientate? --Trovatore (talk) 23:16, 17 December 2009 (UTC)[reply]

If I'm reading the sublimation article correctly, it seems that sublimation occurs at the triple point. So it would be safe to say that its subliming if what Trovatore described is what is happening. Thing is, on the water article it notes that while the triple point of water is nearly at the freezing point, the triple point is also at a pressure about 1⁄166 of normal sea level pressure. I don't think my freezer is also a decompression chamber. Nor is it on Mars. Zhatt 23:35, 17 December 2009 (UTC)[reply]

The triple point is where the partial pressure of water vapour is below 1/166 atm, the total pressure can be far more. --Tango (talk) 17:49, 18 December 2009 (UTC)[reply]

The simple answer is I bet you just have a freezer with auto-defrost, in australia we call it "frost free". I'm surprised no one has mentioned it already, it has been very common in freezers for years. Vespine (talk) 00:00, 18 December 2009 (UTC)[reply]

The process is really no different from evaporation. Even though the ice is a solid - the molecules are still jiggling around (as they will anytime the temperature is above absolute zero) - and once in a while, one is going to get knocked out of position and go flying off someplace else. The air inside a freezer is very dry indeed - so the odds of any stray water falling back onto the ice is vastly less than any from the ice ending up elsewhere - so slowly but surely, the ice-cubes get smaller. Now - whether it's subiming or sublimation or evaporation or some other thing is purely a matter of vocabulary. The effect is that the water goes from ice to vapor without ever having been a liquid in between - while being at a temperature below it's melting or boiling point. But that's not really the same as the way that (for example) dry ice goes straight to CO2 gas when it warms above it's melting/boiling point. The underlying mechanism is the same - but it's a matter of degree. In humid sub-zero air, the ice would gain volume as fast as it loses it - but the dry ice is hitting it's boiling point and it's going away, no matter how much CO2 gas is mixed into the air. SteveBaker (talk) 00:47, 18 December 2009 (UTC)[reply]

SteveBaker is right. Ice sublimes perfectly fine at temperatures well below the freezing point (the triple point is irrelevent, since your freezer is not anywhere near the correct pressure to be at the triple point). Inside of a block of ice, molecules are vibrating at multiple speeds; some are vibrating fast enough to overcome the lattice energy of the ice. Doing so means they seperate from all of the other molecules around them... They become a gas. Its exactly the same as a liquid evaporating. There is no functional difference between a solid and a liquid in these events. Lots of other solids are as volatile as ice; some much more so. Naphthalene for example is a solid at room temperature, and sublimes even more readily than does ice. --Jayron32 03:13, 18 December 2009 (UTC)[reply]

Refrigerators and freezers are extremely dry. They have almost no humidity at all. So ice can evaporate very easily. Water will evaporate at temperatures well below boiling. The lower the humidity, the faster water evaporates. In a freezer (and fridge, since they are connected), the humidity is so low, ice will evaporate. See here [29] - it seems that ice will evaporate down to about -12c/8f and most freezers are kept warmer than that. But note that the freezer coils ARE colder than that. So the ice evaporates, and then condenses on the freezer coils - this keeps the humidity of the air in the freezer very low. Ariel. (talk) 08:24, 18 December 2009 (UTC)[reply]

Jello

Does Jello still have horse hooves in it? --71.144.122.81 (talk) 23:49, 17 December 2009 (UTC)[reply]

Our Gelatin article says: Gelatin (from French gélatine) is a translucent, colorless, odorless, brittle, nearly tasteless solid substance, derived from the collagen inside animals' skin and bones. Comet Tuttle (talk) 23:52, 17 December 2009 (UTC)[reply]

So they don't have any way to make it synthetically? --71.144.122.81 (talk) 00:04, 18 December 2009 (UTC)[reply]

Make what synthetically, horse hooves? hydnjo (talk) 00:19, 18 December 2009 (UTC)[reply]

Collagen. It's just a chemical compound, so there must be some reaction or series of reactions which can produce it. --71.144.122.81 (talk) 00:21, 18 December 2009 (UTC)[reply]

Yes - but perhaps not economically. SteveBaker (talk) 00:36, 18 December 2009 (UTC)[reply]

There are a number of Ghits for "vegetarian jello" though... Dismas|^(talk) 01:10, 18 December 2009 (UTC)[reply]

But these are usually based on agar-agar (seaweed-derived), guar gum (guar bean-derived) or other such polysaccharides, rather than synthetically produced gelatin. -- 128.104.112.87 (talk) 16:01, 18 December 2009 (UTC)[reply]

People in the English-speaking world tend to get somewhat irrational when it comes to horses in food - but I very much doubt that horse hooves are actually available in sufficient numbers to met the vast amount of jello that's produced. Complying with food safety standards with horses would also be a nightmare because they aren't farmed commercially for the purpose. Cow hooves and skin are just as applicable. These are waste products that are presumably cheap and in plentiful supply - they would likely be wasted if we didn't use them for stuff like this. So I would be very surprised to hear that horse hooves are actually used for making Jello. Cow hooves is much more likely - maybe pig trotters - who-knows-what bits of chickens and turkeys. SteveBaker (talk) 01:49, 18 December 2009 (UTC)[reply]

Actually, its a Good Thing!!! that Jello and products like it use animal hooves and other waste products in their production. One of the "criticisms" of meat consumption is that it is wasteful; not all parts of the animal get used. Its applications like Jello (and Glue, and other uses) which help to ensure the efficiency of the system. Its using every part of the animal, which can't be bad, unless you object to eating animals because they have have more biological rights than do plants... --Jayron32 03:07, 18 December 2009 (UTC)[reply]

Or if you don't want to eat stuff made from hoof and skin, a great substitute little known in the west but very common in Asia is agar. Mind you some people might find the idea of seaweed just as unappetising as hoof but let me assure you it is quite tasteless and you can flavour it however you like. I personally think it's much nicer then jelly, it sets a bit firmer which i like, it's not as "sloppy", but it is still unmistakably jelly "like". I've learned a recipe for coconut jelly and it is a really impressive but simple dessert to make. I don't see why you couldn't use more traditional western flavours. Vespine (talk) 04:49, 18 December 2009 (UTC)[reply]

I would say agar is fairly well known in the west among biological scientists (and there must be quite a few on the RDS). I agree with you it's not commonly used for deserts though. I made a post a while back which discussed some issues relating to this a bit Wikipedia:Reference desk/Archives/Humanities/2009 November 11#Gelatin, whey, and lard vs. Islam. A key point which I raised there of relevance here is that a fair amount of the gelatine comes from pig parts. Take a look at the gelatine article. Cow/Beef/Bovine gelatine is also quite common although that may be used for halal products and sold to Muslim countries (however there's some dispute over whether the cows need to be slaughtered in a Dhabīḥah ḥalāl fashion) and perhaps for Kosher gelatine (again the cows may have to be slaughtered in a Kosher fashion and it's possible fish gelatine is more common for that purpose). In particular I suspect if the gelatine doesn't say it's more likely to be pig/porcine then cow/bovine/beef although it could be both and vary. There are ways to identify it [30]. I agree horse gelatine is only a tiny proportion of the world's supply if anything. Incidentally back to the agar-agar point, as you say deserts made from it are a lot firmer. I personally like both. Even in Malaysia, with gelatine jellies are quite uncommon gelatine may still be used in sweets, Western influence desserts and other food products and there is increasing interest in halal gelatine which I think highlights the fact there's no simple substitute. Of course that makes problems for Hindu consumers since the halal gelatine is usually cow/bovine/beef. Fish gelatine is also on the rise I believe with new methods of production being researched (seems to be of interest to Thai reseachers in particular) which will likely fulfill the needs of both Hindu, Muslim and Jewish consumers but not vegetarians ones of course. Nil Einne (talk) 06:04, 18 December 2009 (UTC)[reply]

December 18

Lone pairs

Why do lone pairs affect the shape of a molecule? --71.144.122.81 (talk) 00:53, 18 December 2009 (UTC)[reply]

See VSEPR. Because the lone pairs are still electrons and the still repel other electrons. Lone pair electrons will push away bonding electrons just as well as bonding electrons push each other away. In fact, lone pairs have a greater repulsive effect than do bonding pairs because the lone pairs are more localized around the central atom, and thus more "concentrated" and thus have a greater repulsive force associated with them. Thus, you have a situation where the bonding angle in a tetrahedral system like CH₄ is about 109.5^o, while in H₂O, which is still a tetrahedral system like CH₄, the bonding angle is 103.9^o; the lone pairs around the oxygen have more repulsive force than do the bonding pairs between the oxygen and hydrogen. --Jayron32 03:19, 18 December 2009 (UTC)[reply]

As part of that idea, they also represent the same sort of "directionality" (taking up position and space) as if they were a bond. So ammonia, NH₃, still has four pairs like methane does, and therefore still has approximately tetrahedral geometry. DMacks (talk) 05:16, 18 December 2009 (UTC)[reply]

Getting your car hot.

Here is an ongoing debate at my local car club - which is rising to annoying proportions! The question is as follows:

The inside of my car is really cold - I turn the "heat" control to max - but how should I set the blower to get the car warm quickly? It seems to me that if I turn the fan on really high - then the cold air won't be in contact with the heater core long enough to get as warm as it could be - and the high air flow is pushing whatever warm air is in the car out and replacing it with cold outside air. On the other hand, if the fan speed is too slow, the air in the heater core would mostly be close to the same temperature as the core - and Newton's law of cooling says that it won't pick up as much energy as it could if it were cooler.

I bet we don't have an article about that - and I don't think it's possible to come up with a solid answer to this based on theory alone...so we're left with experiments.

Now - I've done the experiment every work day for the last 10 days (as best one can with varying ambient temperatures) - and according to my measurements - keeping the airflow low gets the temperature up faster than having the fan on the maximum setting (the opposite of what I guessed - which is interesting). A couple of other people found the same thing (albeit without resorting to actual stop-watches and thermometers as I did) - but since we're a MINI Cooper car club - and our cars are all pretty much identical - that doesn't prove a general point.

So - here's the question - it this finding true of all cars? Does anyone here (with a different kind of car) have some more data points? Is anyone interested in doing some actual science? (OK - this is going to be WP:OR of the worst kind...forgive me!)

SteveBaker (talk) 01:03, 18 December 2009 (UTC)[reply]

My understanding is that there's no point having the fan on until the thermostat opens up. All you're doing is blowing cold air into the car. --Trovatore (talk) 01:09, 18 December 2009 (UTC)[reply]

That's true - but if the car has been sitting out all night (which is an unstated assumption here), the interior is as cold as the outside air - so there shouldn't be any harm in putting the fan on so that as soon as the thermostat opens up, it'll blow warm air. This actually touches on another question that came up in our club's mailing list...In cold weather, I habitually drive in a lower gear than usual to get the engine up to temperature sooner. This certainly works - but does it waste fuel (because you're running higher revs than you need to) or does it save gas (because the engine runs inefficiently while it's running cold - so getting it up to temperature sooner is good)? On my MINI - which has twin turbo's - driving one gear lower until the car gets warm does indeed save gas - the jury is still out on non-turbo MINI's. SteveBaker (talk) 01:27, 18 December 2009 (UTC)[reply]

Well, the interior won't be quite as cold as the outside air — if nothing else, some of your own body heat will warm it up. Not a large effect, but in a small car, especially with passengers, it might not be negligible. More important from a practical point of view is that moving cold air will suck heat from your body faster than still cold air. --Trovatore (talk) 02:09, 18 December 2009 (UTC)[reply]

I'd love to help you Steve, I've got a thermometer and a stopwatch... but it's summer and I don't have an air-conditioned garage. --203.202.43.54 (talk) 01:49, 18 December 2009 (UTC)[reply]

and yes, it does use more fuel to drive in a lower gear. But you can't call it a waste if you want the heat. It should be obvious by the fact that you're warming the engine more quickly - that heat has to come from somewhere. The somewhere is the increased friction from faster moving engine parts... unless your mini has frictionless bearings running in vacuum. As an aside, apparently your lowest fuel usage (on flat road) comes at the lowest throttle setting (that doesn't lead to the engine lugging) in your highest gear. --203.202.43.54 (talk) 01:53, 18 December 2009 (UTC)[reply]

Oops, I didn't read the question properly. As a comparison to running with a cold engine for longer, it's hard to say - I presume your car has a near instantaneous fuel efficiency display, so you should be able to compare fuel used in the first couple of kilometers of a trip following the same path using each method. --203.202.43.54 (talk) 02:13, 18 December 2009 (UTC)[reply]

SO I'm sitting here reading through this long, detailed question and the entire time I'm thinking man, SteveBaker will be all OVER this! and then I get to the end and I see that... he was the one who asked it. I'll be damned! 218.25.32.210 (talk) 03:16, 18 December 2009 (UTC)[reply]

My personal experience - and I've had several cars: Chevrolet Caprice, Ford Mustang, Pontiac Sunbird, Volkswagon Rabbit, Saturn SC1, and a Toyota Corolla (I've excluded motorcycles as they don't apply)... The heater won't be hot until the engine warms up. That is not necessarily a given. The heater core could heat without the engine running as it is electric itself - but my experience is that it doesn't. Only in the Caprice (which was modified as a police car) did the heater blow how air without the engine running. So, that is the first thing to check. Will your heater blow hot without the engine running? If not, then the heat is obviously relative to the engine temperature. The heat of the engine is relative to the RPMs since it is obvious that the engine gains heat with every tiny little explosions inside each cylinder. However, driving the car in cold weather cools the engine - cold air blows through the grill and across the engine. So, to get heat as soon as possible, I let the engine idle. Most engines (all that I've had) run in a "choked" mode when they are cold and idling. The engine idles at a slightly higher RPM than normal. So, it warms up rather quickly. I can time it because it takes me 10 minutes to drive from home to work (and 10 minutes from home to WalMart, 10 minutes to Target, 10 minutes to Piggly Wiggly, etc... Everything is approximately 10 minutes away in different directions). If I immediately start driving, I don't get any hot air before I'm done driving. If I let the car warm for about 5 minutes (I'm a bit OCD, so I actually watch the clock and feel weird if I don't let it wait for a multiple of 5 minutes), the air blows hot shortly after I start driving - well under 10 minutes. The weird thing is that none of the cars vary much as to how long it takes to blow hot - and the engines are all very different. So, that is something you can experiment with. Judge how long it takes to get hot (not warm) air from your heater while driving. Then, wait 5 minutes with the engine running and then start driving. Does it get hotter quicker (including the 5 minutes waiting to start driving)? I must note that I do the 5 minute warmup easily because I go start the car with one kid, go back to get the other kid, go back to get whatever junk needs to go on the trip, and then start driving. -- kainaw ™ 03:35, 18 December 2009 (UTC)[reply]

You say [t]he heater core could heat without the engine running as it is electric itself -- I don't believe that's true for any of the listed vehicles. Generally the heater runs off hot coolant coming out of the engine, before (well, I expect it's before, as it makes more sense to me) it goes into the radiator. Or maybe the heater just redirects the air going through the radiator itself? But in any case it's not electric. I suppose an electric car would have to have an electric heater, if it had any heater at all. --Trovatore (talk) 03:40, 18 December 2009 (UTC)[reply]

I think prestige cars are a little different if they have fancy climate control systems, but in the vast majority of cars the heater generally has it's own little heat transfer "radiator" separate from the car's main radiator. It's something to note if you are going to be driving through a desert or very hot climate, if your car is in danger of overheating and you are desperate to keep driving you should turn the heater on as high as possible because it actually helps with cooling the engine. Obviously you'll want to point all the vents away from yourself and open all the windows, but it actually has a noticeable effect on the running temp of the engine if it is already getting hot. Vespine (talk) 04:35, 18 December 2009 (UTC)[reply]

Police cars have electric heaters because they spend a lot of time parked with the engine off. That explains why the Caprice did that - it had been modified. Most cars only get heat from the water circulating around the engine. The heater core is just like the car's main radiator. In fact, if your engine is overheating, turning the heater on full blast may well get you home without a dead engine! SteveBaker (talk) 05:14, 18 December 2009 (UTC)[reply]

I meant to relay that since the heater is an "electrical" device in the car and you can turn it on without the engine running, it is not obvious that it won't heat up without the engine running. But, the main point is that I've experienced the heater getting hotter quicker by idling in the "choked" mode where the engine idles a bit higher than when I'm driving. Every car I've had initially idles high just like when I pull the choke on a tractor or old motorcycle. I assume it is doing the same thing - running a little high to adjust for the cold engine. -- kainaw ™ 05:56, 18 December 2009 (UTC)[reply]

All this text and no answer? The answer is the faster the fan the better. Newton's law of cooling states that the rate of transferring heat from one object to another depends on the difference in their temperature. i.e. transferring heat from a 10° object to a 30° is MORE than twice as fast as from 10° to 20°. (For how much more, measure temperature in kelvin.) So, when you blow the fan fast, the air spends less time in contact with the heater - yes. But at the same time, it's absorbing heat faster, because the difference between the air and the heater is maximized. Contrast to a slow fan - it spends more time on the heat, but the difference in temperature is less (since the air warms up from the heater), so it's absorbing the heat slower. Ariel. (talk) 08:16, 18 December 2009 (UTC)[reply]

Except that you're wrong. In my tests, the car got warmer faster with a slower air flow. I agree about the law of cooling - and I mentioned that in my question - but that effect is being fought by the fact that a high fan speed is moving more cold air through the heater core and pushing already warmed out out of the car. So you're losing energy overall because of that. The problem is whether my finding is true of all cars - or just cars with the exact properties of the MINI. SteveBaker (talk) 13:34, 18 December 2009 (UTC)[reply]

All (most? some?) cars have a recirculation mode - it's usually called "Max A/C", but works just fine for heating too (if you have a button to turn your A/C on/off). But even without that, I think your test is being affected by your own body heat, because unless the temperature from the vent is colder than the air inside the car (and how could that be possible, since the vent air is what heated it in the first place), you can never loose by getting more of it. At full speed you are still getting warmer air than the air inside the car - except if your own body is heating the space. Ariel. (talk) 18:21, 18 December 2009 (UTC)[reply]

Without recirculation the interior of the car could never get hotter than the air coming from the vent. So if the air with the heater on max blower goes from -10 C (outside) to 20 C then you never get warmer than 20 C. By contrast, turning down the blower might allow the air to go from -10 C to 30 C in the heater, in which case the car could warm to 30 C. It would take longer, but ultimately get warmer. This simple example shows that max blower can't always be the answer for maximum warming. Dragons flight (talk) 18:30, 18 December 2009 (UTC)[reply]

More than twice as fast? I don't follow. Since Newton's law involves temperature differences, we don't need an absolute temperature scale. As far as the subquestion of "what is the heat flow rate in the air coming off the heating element" goes, that's just

F(v)=(T(v)-T_{0})cAv

, where the temperature of the heated air depends on its speed (because slow air has more time to heat up),

T_{0}

is the air's initial temperature (which doesn't count for heating the car), c is its volumetric heat capacity, and A is the duct area. If we use a zero-dimensional model for the air-heater interface,

T(v)=T_{h}+(T_{0}-T_{h})e^{-Kl/v}

, where K describes the quality of contact between the heater and the air and l is the length of that contact (so that

l/v=t

). Of course,

\lim _{v\rightarrow 0}T(v)=T_{h}

and the heat flow drops to 0 when the velocity does. At very high velocities, let

s=1/v

and expand in a Taylor series:

F(1/s)=(T(1/s)-T_{0})cA/s=(T_{h}+(T_{0}-T_{h})(1-Kls)-T_{0})cA/s=(T_{h}-T_{0})KlcA

, where the velocity doesn't matter. We get a maximum (if not at infinite velocity) when

0=F'(v)=cA(T'(v)v+T(v)-T_{0})

, so

0=(T_{0}-T_{h})Kle^{-Kl/v}/v+(T_{0}-T_{h})(e^{-Kl/v}-1)=(T_{0}-T_{h})((Kl/v+1)e^{-Kl/v}-1)

, so

e^{Kl/v}=Kl/v+1

. But that never happens except when

Kl/v=0

, so running the air faster is always better (in this simple model). By using the same

T_{0}

in the expressions for

F(v)

and

T(v)

, I'm assuming that you're recirculating inside air, which is obviously better in realistic scenarios where the car starts at the outside air temperature. --Tardis (talk) 15:34, 18 December 2009 (UTC)[reply]

I wasn't trying to be mathematically exact, I was just trying to explain a concept. I did write that for the actual amount use kelvin. Ariel. (talk) 18:21, 18 December 2009 (UTC)[reply]

Box model. I am going to approximate the air in the heater as having a uniform temperature. Though not entirely true since there will be a temperature gradient between the front of the heater and the end of the heater, it is close enough to true to allow one to examine the dynamics.

Let there be four temperatures: outside air (T_out), air in heater (T_warming), air in car (T_car), and the heating element (T_heater). Further, let the volumetric air flow rate be R, the density of air be ρ, the specific heat of air be c, the volume of the heater by V_warming, and the volume of the car by V_car, the thermal transfer coefficient between the heater and the air in the heater be k_heater, and the thermal transfer between the car and the outside be k_car. Then we have:

$\rho V_{warming}c{\partial T_{warming} \over \partial t}=\rho Rc(T_{out}-T_{warming})+k_{heater}(T_{heater}-T_{warming})$

$\rho V_{car}c{\partial T_{car} \over \partial t}=\rho Rc(T_{warming}-T_{car})+k_{car}(T_{out}-T_{car})$

In the quasi-static limit then:

$T_{warming}={\rho RcT_{out}+k_{heater}T_{heater} \over \rho Rc+k_{heater}}$

and you maximize the heat flow into the car by maximizing:

$R(T_{warming}-T_{car})=R({\rho RcT_{out}+k_{heater}T_{heater} \over \rho Rc+k_{heater}}-T_{car})$

Which implies:

${{\partial \over \partial R}R({\rho RcT_{out}+k_{heater}T_{heater} \over \rho Rc+k_{heater}}-T_{car})}=0$

Which after a bunch of math implies the maximum heating occurs if you keep:

$R={k_{heater} \over c\rho }({\sqrt {T_{heater}-T_{out} \over T_{car}-T_{out}}}-1)$

Which has some interesting limits. It says that if the temperature inside and outside are the same then the best solution is to turn the blower up to maximum, but that to maintain optimal warming one needs to turn the blower down as the car starts to warm. Also, the optimum air flow is higher when the heater is already warmed up than when the heater also starts out cold. (Note that I haven't considered the ability of the air flow to affect the temperature of the heater.) Dragons flight (talk) 08:10, 18 December 2009 (UTC)[reply]

Hmmm - that's interesting. So my finding that a slower fan speed works best seems reasonable - but may not be the optimum solution. Clearly, I need to do some more experiments and try varying the fan speed from max to min as the car grows warmer. Don't you just love this science stuff? Hypothesis, prediction, experiment, better hypothesis, prediction, experiment, theory! Resulting in warmer feet on the way to work. SteveBaker (talk) 13:34, 18 December 2009 (UTC)[reply]

Don't Minis have the "recirculate the inside air" feature? Clearly recirculating inside air as fast as possible is the best solution. --Sean 14:30, 18 December 2009 (UTC)[reply]

I have always done the same thing as you, Steve. Low fan speed and burn a little extra fuel to warm things up. I do know that I have always practiced keeping the heater fan on low speed simply because it makes the car feel even colder to trun it up on high right away, bascially because of the intial pushing of cold air against me. 10draftsdeep (talk) 14:41, 18 December 2009 (UTC)[reply]

Internally recirculate the air? How utterly reasonable. Design a better mousetrap why don't you. Dragons flight (talk) 14:44, 18 December 2009 (UTC)[reply]

Just to muddy the waters a bit more, we need to keep in mind that there are at least two scenarios that we need to account for regarding why the car is being warmed. In scenario one, you want the car to warm up while you're outside the car scraping off the windows and sweeping off the snow. In scenario two, you're inside the car and just need the temperature to become tolerable before you head out on your merry way. If you're outside the car, you want to crank the fans and everything else before you get started. The cold air that initially will be blowing around won't bother you as you're outside the car and as soon as the air is slightly warmer it will begin to act on the interior fog/frost on the windows. If you're inside the car, having freezing air blowing at you is distinctly uncomfortable, so you should keep the fans down; getting the car marginally warmer (maybe!) is of limited value if you're just spent the last few minutes in a 0°C wind tunnel. Matt Deres (talk) 15:14, 18 December 2009 (UTC)[reply]

i think that you should keep the fan off untill the water in the radiator is hotter by the engine , because while you'r in the car isolated from the outside heat exchange will be as slow as it could be,therefore you'r body would'nt lose much heat (you wan't feel colder),if you turn the fan on cold air,(colder than you'r skin tempreture),air will contact you'r skin and gain heat from you making you feel cold,so the wright thing to do is to wait until the cooling water is gaining much heat from the engine then you can turn the fan on,and start to heat you car--Mohammed jaafreh (talk) 16:24, 18 December 2009 (UTC) . —Preceding unsigned comment added by Mohammed jaafreh (talk • contribs) 16:22, 18 December 2009 (UTC)[reply]

If each spatial dimension extends in two dirrections, why does the time dimension only go in one?

We live in a three spacial dimenmsion and one time dimension world (I mean dimensions that we see and experience, I know that according to string theory there are curled up six dimensions everywhere) and when we talk about dimensions we say that one is forwards and backwards, one up and down, one goes to the left and then to the right, and then forwards through time. What about backwards through time? I know there is a heated debated about time travel; but i am not asking is it possible or not, i am asking why when we talk about time as a dimension do we only considering it in one direction while all the others extend in both ways (forwards and backwards, left and right vs. just forward for time). Why is it that we say that youy can go in either direction on a spaciasl dimension but not on a temporal one, that on a temporal one there is only forwards? Is it possible that we actually live with a different number of dimensions that we experience than four? Could it be that we live in a seven dimensional world where each dimensoin is only one direction along a line insteasd of two (instead of one spacial dimension being forwards and backwards it is actually two, forwards is its own dimension and is backwards is its own, up is its own dimension down is its own dimension instead of up and down being one, this would explain why we only experience time forwards, mabey there is a seperate backwards time dimension that our world does not include, hence our world might have seven diomensions instead of four, up is one, down is two, right is three, left is four, forward is five, backwards is six, and forwards through time is the seventh and are univers does not copntain the backwards in time dimension).

Talking about time as a "dimension" is more of a mathematical convenience than anything physically real. This alone is a complete answer to your question...if time and space aren't the same kind of thing - then there is no reason to expect them to behave similarly. But if you absolutely insist on calling time a proper "dimension" then indeed, you should say it goes forwards and backwards - just like space goes left AND right. We measure time as a 'signed quantity' - it can be positive or negative. You can even argue that we don't really travel "through" time at all - we merely exist at over a span of time just like we exist over a span of space. The only odd thing is that our brains only have memories from the past...this imparts an "arrow" to time that we don't have in space. But there is a physical direction too - because entropy behaves differently in one direction than the other. SteveBaker (talk) 01:34, 18 December 2009 (UTC)[reply]

Steve, time is one of the coordinates of the Minkowski manifold (space-time). There is no reason to exclude it from the list of dimensions of the universe. It is not just a mathematical convenience. Dauto (talk) 04:37, 18 December 2009 (UTC)[reply]

You just described a mathematical convenience! SteveBaker (talk) 05:08, 18 December 2009 (UTC)[reply]

Measuring an interval of 5 feet is just as real and meaningful as measuring an interval of 5 seconds. Both time and space can be usefully thought of as dimensions, though they don't behave the same in all circumstances. Dragons flight (talk) 08:35, 18 December 2009 (UTC)[reply]

Certainly it's just as meaningful to measure distance and time - and also mass, temperature, voltage or any of a gazillion other things. In that sense, mass and pretty much any other quantity you fancy can be treated as coordinates in some kind of phase space - but that's just a convenience - there isn't a physical reality underlying space and time being considered to be "the same kinds of thing". Certainly, one should not be tempted into trying to make analogies between space-like and time-like "dimensions" just because we happen to use the same name for them and can sometimes find it convenient to label points with four dimensions. But one shouldn't confuse a mathematical convenience with reality. Sometimes, when doing computer graphics, I find it convenient to treat points as fourteen dimensional objects with properties like color being "extra dimensions" - but that doesn't make me wonder whether I can treat color like I do space. SteveBaker (talk) 13:19, 18 December 2009 (UTC)[reply]

Your speed moving through space is how far you go in a given time. If I go north, as time passes, I'm further north. Going through time would mean how far you end up in the future after a certain amount of time. You always move through time at a rate of 1. This is because you're measuring in terms of time. You could just as well measure in terms of north. A line extending north-east and south-west would be moving east in terms of north. If you walk north, you're going forward in time in terms of north. If you walk south, you're going back in time in terms of north. In short, time is different because you decided to measure everything in terms of time. If you measured everything in terms of north, time would be normal, but you'd only be able to go forward in north. — DanielLC 07:02, 18 December 2009 (UTC)[reply]

No, no, no. If I go south, I do not end up at a universe with lower entropy. The reason time only moves in one direction is because the state of the universe's entropy only moves in one direction. If I redefine my coordinate system to a moving coordinate system as you describe I don't move backwards in time because redefining my coordinate system does not affect the second law of thermodynamics. --Jayron32 07:12, 18 December 2009 (UTC)[reply]

And furthermore - time is not unique in that regard. You might just as well pick some other property and measure that as a function of distance. You could rewrite what DanielLC said with time replaced by some other property and end up with a statement that still makes about the same amount of sense. I dunno - pick "air pressure" which varies with altitude above the surface of the earth - so I'll also change north/south into up/down. Do that and you get this curious (but just as meaningful) statement:

"Your pressure gradient moving through space is how far you go for a given pressure change. If I go up, as the pressure changes, I'm further up. Going through pressure variation would mean how much you end up at a different pressure after a certain amount of pressure change. You change pressure through pressure at a rate of 1. This is because you're measuring in terms of air pressure. You could just as well measure in terms of up. A line extending up-and-east and down-and-west would be moving east in terms of up. If you climb up, you're going down in air pressure in terms of up. If you climb down, you're going up in pressure in terms of up. In short, air pressure is different because you decided to measure everything in terms of air pressure. If you measured everything in terms of up, pressure would be normal, but you'd only be able to go forward in north."

SteveBaker (talk) 13:19, 18 December 2009 (UTC)[reply]

Something else to think about: It's only a matter of convention that we use "up/down", "left/right" and "further/nearer" as our three dimensions. You could have picked any set of three non-parallel directions instead. You could even use cylindrical or spherical coordinates as your three spatial dimensions ("azimuth, elevation, range" for example). The point being that absolutely all such systems for establishing a position require exactly three numbers - you can't devise a system that needs 4 numbers (without one turning out to be redundant) or one that needs only 2 numbers. The "threeness" of space is completely fundamental, no matter which dimensions you choose to use - you always need three. That's what makes space "three-dimensional" - not that we happen to choose a set of three orthogonal axes to use as our measuring stick. Considered like that, we should not think of three very specific dimensions - but just of a more general 'threeness'. Time is a similar deal - you only need one number to specify a time - and you can't use two numbers without one of them turning out to be redundant. So time is inherently "one-dimensional". SteveBaker (talk) 14:24, 18 December 2009 (UTC)[reply]

Steve, IF your model of space and time where space has an intrinsic three-ness associated to it and time has an intrinsic one-ness associated to it were correct THAN you would be right that a four-dimensional space-time would be (at best) a mathematical convenience. The problem here is that your model is more than 100 years out of date. In fact space DOESN'T HAVE a three-ness associated to it and time DOESN'T HAVE an one-ness associated to it but space and time together DO HAVE a four-ness associated to them. An observer can measure the time of two events t₁ and t₂ and find t₁ > t₂ while a different observer would measure the time of those events and find t₁' < t₂'. That is inconsistent with your one-dimansional time model. Dauto (talk) 19:27, 18 December 2009 (UTC)[reply]

Well, clearly time is distinguished from the other dimensions by the signature of the manifold — the inner product of a timelike vector with itself is negative, whereas the inner product of a spacelike vector with itself is positive (or vice versa depending on your convention). So there are distinguished three dimensions and a distinguished lone dimension. They aren't picked out uniquely, of course.

The interesting thing to me is how easily Steve, who affects to disdain metaphysics, ends up discussing it :-) --Trovatore (talk) 19:37, 18 December 2009 (UTC)[reply]

I find that this video (http://www.youtube.com/watch?v=8Q_GQqUg6Ts) helps a bit. Zhatt 21:17, 18 December 2009 (UTC)[reply]

What is this object ?

What is this screen like object on the right side of obama?--yousaf465' 04:59, 18 December 2009 (UTC)[reply]

A teleprompter. DMacks (talk) 05:03, 18 December 2009 (UTC)[reply]

It's not positioned quite right for a teleprompter. I think it may just be a reflector, to improve the illumination of Obama in the photograph. Dcoetzee 05:09, 18 December 2009 (UTC)[reply]

It's a teleprompter. Tempshill (talk) 05:18, 18 December 2009 (UTC)[reply]

Indeed. It's a teleprompter like in this photo. Dismas|^(talk) 05:53, 18 December 2009 (UTC)[reply]

Since teleprompters came up [31] [32] Nil Einne (talk) 06:23, 18 December 2009 (UTC)[reply]

And see this as well [33] on Obama's heavy reliance on teleprompters.

Wow how value laden was that! "Heavy" reliance? No more so than politicians in the UK, and I wouldn't be surprised to find that it's no more so than other US politicians. It goes with the territory these days. --TammyMoet (talk) 08:54, 18 December 2009 (UTC)[reply]

Well, not always. David Cameron delivered his 2007 End-of-Conferrence speech without a script or teleprompter[34]. It lasted more than an hour; he had a list of bullet points on a chair that he glanced at now and then. Quite impressive. Going back a few years, Harold MacMillan was noted for speaking without notes. Alansplodge (talk) 10:41, 18 December 2009 (UTC)[reply]

Yes, I have seen Shirley Williams give a 45 minute talk on data privacy without notes. Using notes used to be for wimps let alone teleprompters but I guess people didn't record and were more forgiving. --BozMo talk 11:11, 18 December 2009 (UTC)[reply]

I note you've quoted opposition politicians here. I suppose it could be said that it's more forgivable for politicians whose pronouncements have no chance of being enacted to speak off the cuff! --TammyMoet (talk) 16:15, 18 December 2009 (UTC)[reply]

That cartoon is OK, but this bit from the Onion News Network is better. APL (talk) 16:49, 18 December 2009 (UTC)[reply]

Not that there's almost certainly one to his left as well. Most politicians have adopted this style of having a teleprompter to either side of the speaker. Typically positioned so that he can look all the way to the left side of the audience, and all the way to the right side of the audience and still be able to read his lines. APL (talk) 16:49, 18 December 2009 (UTC)[reply]

anyone here really knowledgeable on Circadian rhythms?

I want to ask a few questions on photoperiodism as well as M and E cells in drosophila, but I want make sure there are specialists on the topic here first. John Riemann Soong (talk) 05:13, 18 December 2009 (UTC)[reply]

Reference Desk protocol is to just ask the questions and not ask for experts first. Tempshill (talk) 05:19, 18 December 2009 (UTC)[reply]

(ec) I know a good bit about circadian rhythms, but won't necessarily be able to answer highly detailed questions about drosophila in particular. Looie496 (talk) 05:21, 18 December 2009 (UTC)[reply]

We'll do what we can :) -- what is the question? --Dr Dima (talk) 05:44, 18 December 2009 (UTC)[reply]

I don't really get the evolutionary as well as mechanistic basis for why SCN would split in hamsters in LL conditions; other than the fact that you see it on an activity graph and that SCNs cut horizontally (as opposed to coronally) show bimodal behaviour in culture.

Also I'm having trouble understanding selective M and E cell ablation experiments. If you knock out M cells, you knock out the source of synchronising pdf -- so why do E cells still induce evening anticipation behaviour? Also, when will ablating E cells affect morning anticipation behaviour? John Riemann Soong (talk) 11:06, 18 December 2009 (UTC)[reply]

I can't address the second question, but for the first question I think the answer is that LL conditions do not occur in nature (except in the far polar regions), and the SCN activity they induce is probably just pathological. Are you aware that in rhythm splitting the left and right SCN run 180 degrees out of phase with each other, and that rhythm splitting of this sort is only seen in hamsters? Looie496 (talk) 17:20, 18 December 2009 (UTC)[reply]

vector or scalar quantity

Is area a vector or sceler quantity? —Preceding unsigned comment added by Munupulu (talk • contribs) 06:38, 18 December 2009 (UTC)[reply]

Vector quantities have value and direction, while scalar quantities only have value. Does the concept of "area" have any directionality to it? Answer that question, and you can answer your own homework question here. I would direct you to our Wikipedia articles on scalar and vector, but they are written primarly for reference by people with advanced mathematics degrees, and are nearly completely incomprehensible to anyone else. Just remember that vectors have direction, while scalars do not. --Jayron32 07:00, 18 December 2009 (UTC)[reply]

There are examples of both: for instance, a differential vector area in a surface integral, and a scalar area of the Earth (by symmetry). Of course, curved surfaces lack a unique normal direction. --Tardis (talk) 07:16, 18 December 2009 (UTC)[reply]

(ec) The answer is context-dependent. Typically, area simply refers to a scalar value, but in the case of an oriented surface, it is very common to express the orientation as a vector with magnitude equal to the (differential or total) area. Nimur (talk) 07:35, 18 December 2009 (UTC)[reply]

The absence of sections of those articles suitable for people who don't have advanced mathematics degrees seems like a failure, in an encyclopedia. I'd improve the articles myself, but I don't have an advanced mathematics degree. If I did, that would probably remove the motivation. Shame. 81.131.30.43 (talk) 11:43, 18 December 2009 (UTC)[reply]

Try vector area. Gandalf61 (talk) 11:56, 18 December 2009 (UTC)[reply]

That's just the surface normal vector. Area is a scalar quantity. SteveBaker (talk) 12:58, 18 December 2009 (UTC)[reply]

I was responding to the previous poster's comment that the other articles mentioned were too difficult to understand. Area can be either a scalar or a vector quantity, depending on context. It would be nice if we had two separate terms, like the distance/displacement distinction for the 1D case, but we don't, so there is some ambiguity. Gandalf61 (talk) 17:47, 18 December 2009 (UTC)[reply]

We also have speed and velocity as two separate terms to help distinguish the scalar from the vector. I just want to add a minor technical neatpick that area is in fact a pseudovector. Dauto (talk) 19:34, 18 December 2009 (UTC)[reply]

Autonomous behaviour on Guitar Hero

If you play Guitar Hero or Rock Band for any length of time you tend to progress as follows:

You start off by consciously watching the notes and painstakingly learning the finger positions for the keys.
You've memorised the finger positions but you still consciously process the scrolling notes.
You reach a point where you can play by just watching the notes scroll down. You think about them automatically without having to concentrate.
Like #3, but MORE. You don't even think any more and tend to completely "zone in", it's as if you are subconsciously processing the notes and playing them before they even register on your brain. This is especially true of complex note sequences where your hands are definitely working faster than your brain, you only realise what note sequence you've played after it has already passed or if it repeats.

Besides the fact that I'm spending WAY too much time playing games, what is happening at #4? It is not a matter of memorisation either. Last night I played a new song with a tricky note sequence and automatically snapped into autonomous mode. Where does the processing take place in this case? Also, are there any WP articles or studies out there (especially related to GH rather than computer games in general). Zunaid 09:38, 18 December 2009 (UTC)[reply]

No real answer, I think it's called getting in the zone. I try and pay attention whilst driving but still have noticed a couple of times that my hands and feet are doing something before I've realized exactly what it is I'm responding to. Rather strange feeling really, I think I've even got a sense of 'God you're crap, let me do my job' from it as I think about doing something wrong and I've autonomously done the right thing. Dmcq (talk) 11:19, 18 December 2009 (UTC)[reply]

Might be interesting to see what happens in the language center over this learning process. I reckon the difference in processing is that you start out treating the symbols with more general-purpose strategies for decoding and interpretation, strategies which might be suitable for any written language or set of symbols, and the "automatic" behaviour is a matter of using less general-purpose strategies, which could also be called thinking about it less. 81.131.30.43 (talk) 11:50, 18 December 2009 (UTC)[reply]

See procedural memory and muscle memory. Gandalf61 (talk) 11:54, 18 December 2009 (UTC)[reply]

For what it's worth, one of the programmers who worked on Guitar Hero is in the office next to mine at work. He says that they worked very hard to get that kind of progression through the course of the game. It's no accident - it's the result of a lot of very clever design work and careful tuning of difficulty levels, choosing the order of song 'unlocking' and such. SteveBaker (talk) 12:55, 18 December 2009 (UTC)[reply]

Utilization behavior also seems pertinent, or at least funny. 81.131.30.43 (talk) 13:07, 18 December 2009 (UTC)[reply]

Great question...and I must say that getting to #4 is why I play the game. cheers, 10draftsdeep (talk) 14:19, 18 December 2009 (UTC)[reply]

Flow (psychology) seems relevant to this conversation. 206.252.74.48 (talk) 14:50, 18 December 2009 (UTC)[reply]

Some good answers, but not quite there yet. Muscle memory and procedural memory are more to do with practice and repetition, which explains how your fingers can snap to exactly the right positions, but I'm really after an explanation of that autonomous thing where somewhere between your eyes and your fingers something happens that just bypasses your conscious thought completely. It feels almost but not quite like instinct. Maybe I'm under-thinking it though...a lot of the songs actually do have standard "chord" and finger changes so perhaps it is just muscle memory combined with some pattern recognition? Steve, what does your buddy say? Did they actually study this phenomenon in any detail when designing the game? Also, if there are any reasearch papers on this I'd like to have a read-through. My google-fu is failing me. Zunaid 15:01, 18 December 2009 (UTC)[reply]

Didn't see the Flow (psychology) link until after I posted. It seems to be what I'm after but doesn't actually explain the mechanism by which it works. And sadly it devotes exactly one line to its use in game design. Zunaid 15:07, 18 December 2009 (UTC)[reply]

A single line, with a citation, which leads to an extensive online essay with diagrams and everything. 81.131.31.130 (talk) 16:22, 18 December 2009 (UTC)[reply]

Unfortunately there isn't a single universally used term for the phenomenon -- maybe "overlearning" and "automatization" are the most commonly used. For what it is worth, here is a link to a recent paper that examines what happens in the brain during the process. Looie496 (talk) 17:53, 18 December 2009 (UTC)[reply]

For what it's worth, I get the same thing playing an instrument I've been playing for many years: the information seems to go straight from the page or the sound in my head to my fingers (and respiratory system, where relevant). So there might be stuff written about musicians which would be relevant: I know there's a lot written about how musicians read music. 86.178.164.251 (talk) 18:13, 18 December 2009 (UTC)[reply]

I'm with 86.178... The same sort of thing happens with playing a real guitar. Early on, I spent lots of time concentrating on making the chord shapes and learning strumming patterns. Now, I instinctively know, by listening to the rhythm of the song, when to strum and what patterns to use, without thinking about it. Its kinda automatic. Plus, you get better with things like chord progressions, I can now pretty much do the same thing with my left hand work. If I know the key a song is in, and I hear it once or twice, I can pretty much follow along with the changes automatically, without thinking of it. --Jayron32 18:58, 18 December 2009 (UTC)[reply]

Let me quote the first paragraph of the paper I cited above: "Motor skill acquisition is characterized by three main phases: a highly attention-demanding early phase, an intermediate phase characterized by more established performance levels, and an automatic phase (Fitts and Posner, 1967; Schneider and Shiffrin, 1977; Schmidt and Lee, 1999). Both accuracy and stability of the to-be-learned task improve rapidly across the early phase and then advance more gradually until asymptotic performance is reached. Extended practice beyond this point is defined as the automatization or overlearning phase, which is characterized by feedforward instead of feedback control (Wolpert et al., 1998; Miall et al., 2001), allowing the performer to divert attention to other tasks (Schaffer, 1975; Nissen and Bullemer, 1987; Duncan, 1995; Passingham, 1996)" Looie496 (talk) 20:00, 18 December 2009 (UTC)[reply]

Science help desk thank you for Christmas

Well it probably breaks all the rules but as thanks for the advice on the last tree here is a photo of the sun rising this very morning behind a chestnut tree in the front lawn. Its the first year I have really been following the reference desk and there is a WWI tradition for ignoring rules on your first Christmas. Clearly it just snowed and as a non-artistic nerd I kind of liked the photo. The other one is behind the children-proof fencing round the moat in the background. Merry Christmas and thanks to everyone. --BozMo talk 10:06, 18 December 2009 (UTC)[reply]

You're calling a christmas truce? :) 81.131.30.43 (talk) 11:56, 18 December 2009 (UTC) [reply]

Chocolate will be exchanged. Soccer will be played - trolls versus regulars. Machine-gunning of the former by the latter will resume bright and early on the 26th - except in the Humanities desk where the truce will continue into the new year. SteveBaker (talk) 12:51, 18 December 2009 (UTC)[reply]

One wonders whether trolls will be kept out by a moat, or attracted to it for all the underbridges. --Sean 14:36, 18 December 2009 (UTC)[reply]

I know many people disagree, and others think I am being pedantic, but to me "chestnut tree" means a tree of the genus castanea which produces the edible nuts known as "chestnuts". It is true that the expression "horse chestnut" is colloquially used to refer to various species of the genus aesculus, quite unrelated but with inedible nuts of superficially similar appearance; nevertheless I feel that using the word "chestnut" for these trees is misleading. Thus I would say "the sun rising this very morning behind a conker tree", but would accept "behind a horse chestnut tree". Happy Christmas anyway. JamesBWatson (talk) 15:13, 18 December 2009 (UTC)[reply]

So how can you tell from the picture (i.e. ignoring BozMo's revelation below) that this an Aesculus rather than a Castanea? (Pulls out own pedantic hat - the names of genera are always capitalized.) Without leaves and covered in snow I'm not sure how you would identify the tree. -- 128.104.112.87 (talk) 15:56, 18 December 2009 (UTC)[reply]

Ah, trees. This could be a long thread. Certainly this is an Aesculus but locally anyway the edible ones are known as "Spanish chestnuts" or "Sweet chestnuts". In war time people discovered nuts of aesculus can be eaten too, but they have to be cut very fine and boiled for four or five hours first I believe. I have planted a Spanish chestnut (there are fine ones in Ickworth House nearby so I know they do grow here, but the garden has eight mature Aesculi). Sadly I think this tree has only a dozen years of life left, you can see bracken fungus on the left of the truck, a replacement Lime tree is off shot to the left. There are a lot of big dead beech trees in the garden too (cause unknown). --BozMo talk 15:37, 18 December 2009 (UTC)[reply]

Well since people are already talking nonsense... I have to complain that the photo hardly seems Christmasy. It's some tree covered in snow! Who has snow during Christmas?? That's winter stuff and not something anyone wants to think of during Christmas! Please use a more appropriate picture next time, one more suited to a typical summer Christmas. You can have rain if you want. But no snow please! Nil Einne (talk) 16:11, 18 December 2009 (UTC)[reply]

Dare I point out that more people live in the temperate climates of the northern hemisphere then the southern? Googlemeister (talk) 16:16, 18 December 2009 (UTC)[reply]

Yes, per WP:NPA and WP:Civility you really shouldn't be pointing out that most people are stupid. You know that, I know that, no need to rub their noses in it, eh? Nil Einne (talk) 16:40, 18 December 2009 (UTC)[reply]

Can we point out on that basis "not being stupid" correlates with "having convicts as ancestors" then? :). Although to be fair my own great grandfather was a gold miner in New Zealand but came back... --BozMo talk 16:50, 18 December 2009 (UTC)[reply]

I think you're confusing us with some other country. While some convicts were sent here [35], most Kiwis** don't have convicts as ancestors (except for those from that other country who invaded, but we accept them as our own since we're a generous people) at least not any more then the average person (which probably means most do). It's true that people from this other country are largely decendent from convicts (don't worry that this isn't true [36], they're all still sleeping and won't understand this anyway) and it shows, but we try[37] not [38] to [39] hold [40] it [41] against [42] them (not that it matters [43] [44]). At least no more then we hold it against those rebel colonists who were always a bunch of odd people and carried out one of the first recorded acts of large scale water pollution and like to play big bully if you don't let some of their ships in. **You're welcome to bring up a bird in reply to this discussion. But if anyone brings up any fruit whose name should under no condition be shortened to remove the fruit suffix, it's assumed they've decided to end participation in this discussion Nil Einne (talk) 18:22, 18 December 2009 (UTC)[reply]

I had no idea the name of that fruit was such a contentious issue. To avoid potentially causing offense, I think we should all revert to using the transliteration of an earlier Chinese name, and call them hairy bush fruit. 213.122.49.177 (talk) 19:22, 18 December 2009 (UTC)[reply]

It's not so much contentious as an obviously silly shortening. It's like going to the fruit market and asking for a star, dragon, passion, jack, bread or egg. Or perhaps a snake. Nil Einne (talk) 20:12, 18 December 2009 (UTC)[reply]

If its any consolation the first version three years ago of the Schools Wikipedia had Brussels Sprouts listed as a place name (see [45]). --BozMo talk 20:25, 18 December 2009 (UTC)[reply]

Where was the photo taken please? Was it in Britain, as we've had some rather rare snow recently? Nice pic. 78.147.233.150 (talk) 16:55, 18 December 2009 (UTC)[reply]

Barnardiston Suffolk UK at 0908 this morning. Just added one to that article taken of church at same time. --BozMo talk 17:00, 18 December 2009 (UTC)[reply]

Nice, but it will look silly in August. And since we only get laying snow on 2 or 3 days a year on average in that region, then a photo of less than 1% of the year is not a true representation. 89.243.91.31 (talk) 21:16, 18 December 2009 (UTC)[reply]

Why isn't the sky bright white at night?

If there are an infinate number of stars then the sky ought to be blazing white at night, as a star will be at every point in the sky. Even if there are not an infinite number of stars, there are still very many of them and would produce a similar effect. I recall this paradox was made known by a Victorian gentleman, and that there is a modern explaination(s). Can anyone supply more details please? 89.241.43.33 (talk) 13:30, 18 December 2009 (UTC)[reply]

Olber's paradox. Dragons flight (talk) 13:37, 18 December 2009 (UTC)[reply]

The modern answer is that the universe might be infinite in extent (but maybe not, we aren't sure) - but it's definitely not infinitely old. Since light takes time to get here - the further away you look, the further you're looking back in time. At some distance from the earth, you're looking back to the time before stars and galaxies had ever formed - and then, all you see is the cosmic microwave background - and at some yet larger distance, all you see is the big bang itself - and because there is no "before" that event, no light can possibly reach us from more than 13.5 billion lightyears away. That places a firm limit on the number of stars we can see - and it's far from infinite. The fact that the sky is black represents a rather elegant demonstration of truth of the big bang theory. SteveBaker (talk) 14:03, 18 December 2009 (UTC)[reply]

Well kind of. There are lots of other ways it could work too: non uniform density of stars for example is sufficient to resolve the paradox. But I certainly would argue with it being compatible... --BozMo talk 14:12, 18 December 2009 (UTC)[reply]

Yes - I picked the word "demonstration" rather than "proof" for that reason. SteveBaker (talk) 14:33, 18 December 2009 (UTC)[reply]

Actually even if the universe were infinitely large and infinitely old we would still only see a limited part of it. The red shift due to the expansion of the universe means that after a certain distance the light is red-shifted out of the visible spectrum. What is more, because longer-wavelength photons have less energy, the total energy we receive declines, not just the energy in the visible spectrum. JamesBWatson (talk) 14:59, 18 December 2009 (UTC)[reply]

That's if it was infinitely large, and getting bigger, right? 81.131.31.130 (talk) 16:07, 18 December 2009 (UTC)[reply]

Yes, but we know it's getting bigger. (Well, it's expanding - if it's infinite then its size isn't actually changing, but don't think about that too much, you'll get a headache!) --Tango (talk) 18:52, 18 December 2009 (UTC)[reply]

Um, a universe that is expanding can't be infinitely old unless you posit some dynamics besides the run of the mill cosmology. Just run the movie backward and a currently expanding universe will contract to zero apparent size in finite time. Dragons flight (talk) 19:08, 18 December 2009 (UTC)[reply]

Unless it contracted at a slower and slower rate, under which scheme it would hit some kind of limit, a lower bound of the size. This would mean the universe began at a certain size an infinitely long time ago, and then its expansion accelerated infinitely slowly until we reached present conditions, infinitely later. 213.122.49.177 (talk) 19:36, 18 December 2009 (UTC)[reply]

In addition to the fact you seem to have trouble grasping the meaning of infinity, that description is definitely "some dynamics besides the run of the mill cosmology", meaning you'd need to seriously modify general relativity to get the universe to do anything even remotely like that. Dragons flight (talk) 20:40, 18 December 2009 (UTC)[reply]

Did anyone say otherwise? I was talking about the universe being infinite in size, not duration. I must correct one thing, though - the universe didn't necessarily start at zero size. If it is infinite now then it was infinite at the big bang - it would have also had infinite density, so the volume of what is now the observable universe would have been zero. --Tango (talk) 21:04, 18 December 2009 (UTC)[reply]

Meteorites from Vesta and Mars?

The Vesta article mentions meteorites found on earth from Vesta. I've also heard of meteorites from Mars. How can scientists identify where they come from? And since when have they been able to do this? 78.147.233.150 (talk) 16:58, 18 December 2009 (UTC)[reply]

If we know what the composition of the meteorite is and what the composition of the asteroid/planet/etc is, then we can compare them. The reference for that statement (here) has more specific info (gotta pay, but the abstract says enough). We can also track movements after collisions, and even follow orbits backwards through time. ~ Amory (u • t • c) 18:36, 18 December 2009 (UTC)[reply]

We have an article on the Mars meteorites. The killer piece of evidence is that inclusions within the meteorites exactly match the composition of the martial atmosphere. There is no other body in the solar system with even a remotely similar atmosphere, and if they had come from outside the solar system, that would be even more remarkable. SpinningSpark 20:45, 18 December 2009 (UTC)[reply]

Hawking and the LHC

How does Hawking Radiation stop black holes from forming in the Large Hadron Collider? MMS2013 17:46, 18 December 2009 (UTC)[reply]

It won't necessarily stop them, it will just likely cause them to dissipate in a near-instant. The micro black holes the LHC could theoretically create wouldn't have enough mass to last. The top of Hawking radiation basically says it all. ~ Amory (u • t • c) 18:48, 18 December 2009 (UTC)[reply]

will hairdye

burn yer skin if u touch a spill on the floor thats been out for a few mounths

Probably best to use gloves when cleaning up any chemical spill, even old ones. Dragons flight (talk) 20:42, 18 December 2009 (UTC)[reply]