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April 23

Eyjafjallajökull: Tephra color

Some images and videos of the recent eruption show tephra with distinct black or white coloring. I have two questions about this:

• What is the difference in composition between the differently colored tephra?
• Why are the two spatially separated instead of being one big gray cloud ? Also some videos show purely white or mostly black ash clouds; why does the composition and mix seemingly change with time ?

Abecedare (talk) 02:49, 23 April 2010 (UTC)

Just a WAG, but the white doesn't look like tephra, it looks more like cloud, i.e. condensed water vapor, which may be forming at the boundary conditions between the hot air surrounging the ejecta and the cold, damp air due to melting ice and/or the local humidity. Hot + cold + water vapor = cloud, so that may be more of what is happening with the white stuff. The black is the pyroclastic material itself. --Jayron32 02:59, 23 April 2010 (UTC)

Query: WAG="Wild ass guess"? --220.101.28.25 (talk) 03:08, 23 April 2010 (UTC)

That's right. StuRat (talk) 13:50, 23 April 2010 (UTC)

That could be the case, especially since the volcano is/was topped by a glacier, which would be a prime source for immense amounts of steam. That would also explain the spatial delineation, for the temperature in the immediate vicinity of the erupted ash would be too high to allow for steam condensation and cloud formation. Does anyone know for sure ? Abecedare (talk) 03:24, 23 April 2010 (UTC)

There have been several reports that the white clouds are water vapour and the darker clouds are ash. I can't find one offhand - but it's very clear that this is what's going on. SteveBaker (talk) 12:55, 23 April 2010 (UTC)

Not to be too pedantic, but the clouds are not water vapor. Vapor is a gas, which is invisible. The clouds in the pictures, like all clouds and fog, is an aerosol of liquid water droplets suspended in the air. It is the product of condensing vapor, that is of the water gas collecting into tiny microscopic droplets, that makes clouds visible as white puffy things. --Jayron32 00:53, 24 April 2010 (UTC)

Invertebrate stomach

The article on the stomach does not describe its distribution outside of the vertebrates. The link from Chordata to digestive canal incorrectly redirects to human anatomy so that is of little help. Echinoderms are said to have "stomachs" but it seems doubtful that that structure is homologous with the human stomach. Could someone knowledgeable about this subject help me fill in this gap in Wikipedia? -Craig Pemberton 03:50, 23 April 2010 (UTC)

Be bold. DRosenbach ^{(Talk | Contribs)} 14:32, 23 April 2010 (UTC)

Milk protein denaturation

Why is NOT the protein in milk coagulated/denatured on boiling? I am not sure if the question is already asked, please let me know. - Anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 04:53, 23 April 2010 (UTC)

In of milk, the primary protein is casein. The Wikipedia article on casein itself describes the reason why it does not coagulate. --Jayron32 05:10, 23 April 2010 (UTC)

Thanks. The reason for not being denatured is given but coagulation part is vague. "Casein is not coagulated by heat" but WHY? In industries, an optimal temperature of 43 °C for 4-6 hours is used for preparation of curd (coagulation process?). I wish to know the relation between "In milk, casein is a salt of calcium" and coagulation. May i also know the function of casein? 125.21.50.214 (talk) 06:03, 23 April 2010 (UTC)

Since milk has only one function: nutrition, I would suspect that Casein is the structure it is for ease of digestion. Coagulation is caused by crosslinking between denatured proteins. Denaturing is specifically the loss of tertiary structure. Casein's peculiar organization (it has lots of proline and no cysteine) means that there really isn't any tertiary structure to speak of. It is the breaking of Disulfide bond from a single molecule and the random reforming of those bonds between neighboring molecules that leads to the crosslinking in coagulation. No cystein = no disulfide bonds = no coagulation upon denaturing. Casein, with lots of proline and no cystein, is basically a randomly wrapped somewhat floppy chain of peptides, with nothing holding into any particular tertiary structure. So there is nothing to denature there. The reason it is a calcium salt in milk is because casein's isoelectric pH is much lower than milk's native pH, meaning that it is a negative ion in milk. Being a negative ion, there needs to be a positive counterion which balances its charge, and the most common positive ion in milk is calcium. Hence, it is a salt of calcium in milk. --Jayron32 15:01, 23 April 2010 (UTC)

Cheese is created through heating with the addition of the enzyme rennet (originally sourced from the lining of animal stomaches) and usually addition of acid (sometimes directly in acid-set cheeses, more often indirectly as by-product of intentional bacteria growth) Yum, cheese! See cheesemaking for more including which cheeses must have mold as well. Rmhermen (talk) 13:32, 23 April 2010 (UTC)

Based on my experience with hot chocolate if you bring a pot of milk to boil it will develop a skin of denatured protein on the surface... cyclosarin (talk) 15:13, 24 April 2010 (UTC)

Why exactly do pet parrots mimic (or attempt to learn, if you believe that) human speech?

Is it basically them trying to fit in with humans? WP's talking bird article doesn't explain anything about why. Thanks. --95.148.106.230 (talk) 07:57, 23 April 2010 (UTC)

Birds mimic so that they can learn what sounds they should make, hopefully from more experienced birds of the same species. Graeme Bartlett (talk) 12:47, 23 April 2010 (UTC)

According to this source birds call or sing:

• Calling or singing to attract a mate.

• Calling or singing to establish the bird's territory

• As an indication of the readiness of either or both partners for mating activity

• Maintain a bond between male and female bird

• As a way of communication between parent and young

• As a means of warning it's[sic] mate or other members of the flock of danger

• As a means of gathering a flock together or finding each other

• As a means of encouragement to fellow flock members (such as the case of geese flying and calling to other members to keep up

• As a tactic of intimidation to predators or other birds

• Birds do practice their songs, calling and talking through repetition. Cuddlyable3 (talk) 12:59, 23 April 2010 (UTC)

To answer the Q, rather than talk about why birds sing in general, let me start by saying that some species of birds imitate all sounds they hear. They probably do this to impress potential mates with how fit they are, if they can imitate any sound they hear. This also applies to mimicry of human speech. Of course, if they are rewarded when practicing this (say with food), they may do it even when there's no mate around to impress. StuRat (talk) 13:46, 23 April 2010 (UTC)

Also, since parrots are social animals, when a bird is raised with humans his whole life, he thinks that he is human too. That is one reason they imitate us. --The High Fin Sperm Whale 18:24, 23 April 2010 (UTC)

Many parrot owners don't actually realize this - but pet parrots will often consider the human with which they interact with the most to be their mate. This is basically the reason behind the violent, jealous 'one person parrots'. --Kurt Shaped Box (talk) 04:41, 24 April 2010 (UTC)

See also: Alex (parrot). GeeJo ^(t)⁄_(c) • 19:07, 23 April 2010 (UTC)

Many birds mimic the sounds they hear in their environment, presumably as a means of making themselves more attractive for mating purposes. Also presumably, they have done this for thousands of years prior to the appearance of humans in their environment.

There was a fabulous episode of a TV series on this subject, I think by David Attenborough. One of the exhibits was a bird that had lived all its life in a forest in which logging was taking place. This bird was a brilliant mimic of the sound of a chain saw! Dolphin (t) 05:41, 24 April 2010 (UTC)

In most songbirds, the songs they sing are only partly genetically programmed. There is always a range of possibilities, and a bird learns to sing a specific song by imitating the songs it hears. In most species the range of things a bird will imitate are pretty narrow, but there is a lot of variability, and (as you know) there are some species such as parrots for which the range is extraordinarily wide. Looie496 (talk) 22:11, 25 April 2010 (UTC)

I don't know exactly where I read this but I believe that it's been mentioned on the desk by someone else before too (with a source), that parrots will use mimicry to communicate with specific members of their flock - they 'parrot' the subtle vocal characteristics of the bird they wish to 'talk' to/at. As an aside and in reference to the above, I once saw a YouTube video of a pet Budgerigar that had been hand-raised by humans from the egg - and his vocalizations were extremely strange. Aside from a generic tweet (which sounded un-budgielike, even to my tin ears) and the standard cackle (hard to describe - but it's the one that appears to come from deep in the throat, not the mouth), every other sound he made was constructed from snippets of human speech and noises heard around the home, all spliced together into a song, of sorts. It would be interesting to see what would happen if they placed a budgie with a standard upbringing in there with him - I don't know for certain but based on my personal knowledge of how other parrot species will react to 'humanized conspecifics', I'd imagine that the reaction would be something along the lines of complete bewilderment from both birds, followed by a very difficult process of acquaintance and acceptance, with much fighting. --Kurt Shaped Box (talk) 01:13, 26 April 2010 (UTC)

gravity-south pole

Is the value of gravity same all around the earth? Is that like things/creatures at the south pole has lesser gravity comparitively because it is at the bottom of the earth (seems like clinging to it, things will fall off):-)? How is the south pole affected by earth's rotation/revolution? Is gravity because of earth's rotation (too)? Is the escape velocity same all around the earth? I dont understand physics well!!!125.21.50.214 (talk) 11:29, 23 April 2010 (UTC) anandh.

see here--BozMo talk 11:37, 23 April 2010 (UTC)

The south pole is only the "bottom" of the Earth by modern mapmaking convention (some old maps put East at the top). Gravity doesn't care about up and down; it just pulls everything towards everything else, so there's nothing gravitationally special about the South Pole. Earth is by far the biggest thing near us and gravity is very weak, so, to a first approximation, gravity just pulls us towards the center of Earth.

Now, earth's rotation does have an effect. The centrifugal force caused by Earth's rotation (same thing that causes your arms to be pulled out if you spin around in place fast) causes things to be lighter, the closer they get to the Equator. But things are only 0.3% lighter there than at the poles, so it's not something that you'd notice. Paul (Stansifer) 12:31, 23 April 2010 (UTC)

The shape of the earth has an effect too - the poles are closer to the center of the earth than the equator - hence more gravity there. There are also differences due to mountains - which get you further from the center (hence less gravity). Deposits of denser or less dense rock will also make a difference to local gravity. See Gravity anomaly, Physical geodesy SteveBaker (talk) 12:53, 23 April 2010 (UTC)

The radius of the Earth varies from 6,357 km at the poles to 6,378 km at the equator, and (6,378/6,357)² = 1.0066, so this reason only increases the gravity at the poles by 0.66% compared to the equator. Actually it'll be slightly less than that due to the pull of the equatorial bulge itself, but that's harder to compute. Combining that with the centrifugal effect, which is more accurately 0.35%, we see that you weigh no more than about 1% more when at the poles. --Anonymous, 03:45 UTC, April 23, 2010.

9 volt battery

I often test if 9 volt batteries are still good by touching them on my tongue and seeing if they give a small shock. Would touching a 9 volt battery to a hypothetical persons penis/clitoris produce an orgasmic effect? 82.43.89.71 (talk) 12:22, 23 April 2010 (UTC)

Wikipedia has an article on Nine-volt battery. Connecting the male and female terminals is inadvisable as it leads to premature discharge. Cuddlyable3 (talk) 12:50, 23 April 2010 (UTC)

Premature discharge? Cue rimshot. Kingsfold (talk) 16:14, 23 April 2010 (UTC)

No - if that worked then every sleeze-bag on the Internet would be selling devices that do exactly that. SteveBaker (talk) 13:01, 23 April 2010 (UTC)

That is quite independent of whether it works, and they do. --Stephan Schulz (talk) 13:48, 23 April 2010 (UTC)

See Erotic electrostimulation. PrimeHunter (talk) 16:24, 23 April 2010 (UTC)

Touching the device to the hypothetical person might constitute battery, but we cannot give legal advice. The current from the battery would depend on the resistance. Salt on the skin would likely lower the resistance. We do not seem to have an article on Salt and battery. Alessandro Volta tested his batteries (or "piles") in a similar manner, but by using other parts of his own body. This might be considered "self abuse," and if done to the eyes like by Volta, Ritter or Charles Darwin, might cause you to go blind. Some 19th century writers, going in the opposite direction, speculated that sexual intercourse might be pleasurable because of the electricity generated by the act. 19th century quack "doctors" did lots of truly scary electrical experiments, sticking electrodes about everywhere to prevent "spermatorrhoea," which should absolutely not be imitated. In the late 19th century doctors attempted to treat "female complaints" with electricity, either DC or AC, with mixed results. By the 1970's women started using batteries not directly but instead to power vibrators, and found this an effective way of obtaining orgasms[1]. Edison (talk) 22:30, 23 April 2010 (UTC)

The minute current may stimulate nerves in the genitals like it does to the tongue.This could technically simulate nerve impulses and thus fooling the body into having and orgasm.I highly do not recommend doing this as the genitals are one of the most sensitive organs in the human body and damage to them could be potentially irrepairable.

Global warming.

Cenozoic global temperatures (right-to-left)

This subject has me thoroughly confused! The sea level is rising, caused by melting ice, caused by global warming, caused by increase of carbon dioxide in the atmosphere. That is what it seems to me that scientists have stated. Am I right? If not, then ignore the rest! cdiac.esd.ornl.gov/trends/co2/contents.htm claims that atmospheric carbon dioxide concentration jumped from 275 ppm in 1750 to 367 ppm at present. A WHOLE WHOPPING 33%! TERRIBLE? But that is still only .0367% of what we breathe in. Of course I realize that the increase itself is increasing. BUT: mistupid.com.chemistry/aircomp. gives the present level as 330 ppm. Answers.com gives 380 ppm, Wikipedia gives 387 ppm and Physlink 314 ppm. And if I had searched further I would no doubt have found still different figures! AND: Whilst the increase from 1750 to Physlink is only 14%, the discrepancy between Wiki and Phys is an enormous 23%. When I did chem. anal. half a century ago, if I had come up with such varied answers, my employers would have kicked me out on the spot! LASTLY: National Geographic some years ago stated that (I think) some few million years ago the carbon dioxide in our atmosphere was 5x the present level. AND LOOK WHAT HAPPENED: WE DID!!!!!! Not feeling at all comfortable with a PC, nor with how to reply to an answer (vide my query re EMP weapons in Smolensk a few days ago), could some kind soul PLEASE tell me, step by step, how to go about this? Thank you!!!220.253.193.132 (talk) 13:01, 23 April 2010 (UTC)

I suggest you start with Carbon dioxide in Earth's atmosphere BozMo talk 13:05, 23 April 2010 (UTC)

Some points:

1) Yes, CO₂ levels were higher at times in Earth's history, but so were sea levels. The problem isn't really so much that we are headed to an inherently dangerous level of carbon dioxide, but that we have chosen to build on the shores of oceans around the world, which means that billions of people will be subject to increased flooding.

2) Yes, the level of carbon dioxide is a tiny portion of the atmosphere in total. If the atmosphere was all greenhouse gases, then we would have a planet like Venus, which would kill off all people (and most life) on Earth.

3) Variations in measurements around the Earth can be expected to be larger than those measured in a laboratory setting. There will be variations by location and date, as well as due to different measurement methods. However, all the numbers you listed show an increase; that's the most important part. StuRat (talk) 13:33, 23 April 2010 (UTC)

Just pointing out that StuRat in #1 above says "the problem" is coastal flooding, whereas of course there are many, many other problems. Our Effects of global warming article discusses some. If you take an eons-long view, then it probably doesn't matter to you that, for example, as this article discusses, higher temperatures in the Pacific Northwest are giving the bark beetle a longer seasonal life each year, which has allowed them to kill 10 times as many trees as they have historically — a million years from now, who's going to care about this particular problem, true; but there are knock-on effects from these problems of today that make a lot of people care today. Comet Tuttle (talk) 17:07, 23 April 2010 (UTC)

"...all the numbers you listed show an increase..." It's not like these guys have forgotten how to do statistics. Countless studies show a significant rise that can't be contributed to randomness. At this point in the debate it isn't really a question of whether CO2 is the culprit. It is, and it is making temperatures rise. What is still up for debate is hanging a world catastrophe on changing temperature. If you want to argue against Global Warming give them their entire argument save the global disaster. Yes CO2 is rising due to us, and yes it will probably impact the climate. No matter how strong the correlation of the data and no matter how certain we are that it is our own fault, these facts don't necessitate drastic climate changes that lead to a series of uncontrollable steps where very bad things happen.

Nowadays, you won't find too many reputable sources screaming Armageddon. They have backed off that claim for now, and for good reason. It is pretty uncertain what will happen in the future, even with all the data we have. However, I found a few claims on the Global Warming quite interesting:

"In a literature assessment, Smith and others concluded, with medium confidence, that:

-climate change would increase income inequalities between and within countries

-small increase in global mean temperature (up to 2 °C by 2100, measured against 1990 levels) would result in net negative market sector impacts in many developing countries and net positive market sector impacts in many developed countries

-the aggregate market sector impact (i.e., total impacts across all regions) of a small increase in global mean temperature would amount to plus or minus a few percent of world GDP."

Conclusions like these point to a growing realization that it isn't very likely anything good will come of Global Warming, but the first one seems a little shaky. In my opinion, no one should be trying to speak this conclusively. It is very easy to be wrong when correlating broad trends with temperature. That should be your main line argument, not questioning the research.

Mrdeath5493 (talk) 17:16, 23 April 2010 (UTC)

So, according to you, positive market impact in most civilized countries is not a good thing?! 76.103.104.108 (talk) 01:49, 28 April 2010 (UTC)

Atmospheric CO₂ concentrations lower than 387 ppm are likely outdated. Global concentrations have increased more from 1800 to today (+107 ppm) than it has between the peak of the last ice age to 1800 (+100 ppm). ~AH1^(TCU) 21:40, 23 April 2010 (UTC)

Perpetual motion machine

In string theory, the basic building blocks of matter are said to be tiny vibrating strings. The frequency to which they vibrate determines their properties.

Where do they get the energy for this vibration? If they vibrate forever, they are perpetual motion machines. If they don't, what will the universe look like when all strings have ceased to vibrate? What will be these strings' properties? --13XIII (talk) 14:20, 23 April 2010 (UTC)

Note that only the type of perpetual motion machine where "you can pull energy out and still have it run forever" is impossible. Having an object move forever without removing energy is fine, in a frictionless environment. One of Newton's laws, after all, is that "An object in motion stays in motion, unless another force acts upon it". StuRat (talk) 14:47, 23 April 2010 (UTC)

But doesn't the movement itself remove energy from the string? Since vibration means mechanical oscillations about an equilibrium point, the string would vibrate back and forth. Accelerate back, decelerate, accelerate forth, decelerate, etc.--13XIII (talk) 15:22, 23 April 2010 (UTC)

No. Under Newtonian physics the vibration would give off heat, but strings are too small for those laws to apply. Quantum mechanics rules at those scales. StuRat (talk) 15:32, 23 April 2010 (UTC)

It is not necessary for something that appears to "vibrate" to be accelerating and decelerating. It could be an effect of dimensional perspective. Imagine a merry-go-round spinning. Due to your dimensional limitations, you cannot see the main mechanism. You can only see one horse on it. Further, you can only look it from the side and you cannot sense any sort of depth. What you end up seeing is a horse moving back and forth - but it is not accelerating/decelerating. It is rotating. -- kainaw™ 17:38, 23 April 2010 (UTC)

In a simple piano-string vibration...during acceleration towards equilibrium, the string gains kinetic energy. The acceleration comes from the potential energy of the string being away from equilibrium. During deceleration, the kinetic energy is converted back to potential energy as the string moves past the equilibrium state. There's no net loss of energy, just change of its form. DMacks (talk) 17:56, 23 April 2010 (UTC)

There certainly is a loss of energy from a vibrating piano string, some of which becomes air vibrations (sound). StuRat (talk) 19:34, 23 April 2010 (UTC)

Vibrating objects do radiate away their vibrational energy until they reach equilibrium with the environment. Quantum mechanically, though, the lowest energy state still has some vibrational motion, because of the uncertainty principle. Even in a vacuum, a system can remain in that vibrational state "forever" (though not really forever, because there are probably other allowed decays with extremely long half-lives, like spontaneous fusion or proton decay).

The other thing, though, is that the premise is false. The known particles aren't different vibrational states of strings (assuming that known physics can be reproduced within string theory at all, which still isn't known). They are different vibrational states of the vacuum, but that's already true in ordinary particle physics. It has nothing to do with the stringiness of the strings. I don't know why so many of the popularizations make a big deal about string vibration. Probably it's because then they can talk about the physics of music, a very old and well-understood topic, and pretend that they're teaching string theory. -- BenRG (talk) 19:28, 23 April 2010 (UTC)

If vibrators give off heat, that may explain my singed pubes.--79.76.130.158 (talk) 21:22, 23 April 2010 (UTC)

Atoms are constantly bouncing off each other, but they don't loose any energy by doing so. Energy lost by one atom is gained by another, which then goes to another - as long as no energy leaves the system, it can do this forever. Vibration is the same - it moves one way, stores energy in tension, then retrieves the energy on the way back, and does it over and over. As long as no energy is lost from the system it can do it forever. (With the macro objects friction steals energy.) The only reason perpetual motion machines don't work is that there is friction which steals energy. Otherwise they could actually go on forever (as long as you don't try to do anything with them.) Ariel. (talk) 22:34, 23 April 2010 (UTC)

You must also remember that the string theory is not a fix it all solution.There are many unanswered questions about it.

Antimatter bomb

Assuming equal amounts of fuel, would an antimatter bomb be more powerful than an atomic bomb? What would the explosion from an antimatter bomb look like? --71.144.122.18 (talk) 14:36, 23 April 2010 (UTC)

It would be on the order of 10,000 1000 times more powerful. If you decreased the amount of antimatter to get a similar yield, then it would probably look similar to an atomic bomb. However, a large anti-matter bomb, if it was possible, might rupture the crust of the Earth, causing volcanic effects absent in an atomic bomb. StuRat (talk) 14:42, 23 April 2010 (UTC)

How did you find your way here, without finding your way to Antimatter weapon first?--Aspro (talk) 14:46, 23 April 2010 (UTC)

Modern fission weapons will fission about 40% of their fuel; each atomic fission converts (roughly) 0.1% of its mass to energy; therefore about 0.04% of the total fuel mass is coverted to energy. (See Mass–energy equivalence#Efficiency.) Fusion weapons do better (efficiency-wise), converting about 0.3% of their fuel mass to energy. A matter-antimatter weapon, in contrast, ideally converts 100% of its fuel mass to energy. On a weight-for-weight basis – neglecting the mass of any containment, triggers, delivery system, etc. – the matter-antimatter bomb will deliver 300 times the energy of a thermonuclear fusion bomb and about 2500 times the energy of a fission bomb.

As for the appearance of the explosion, I'm not sure — perhaps StuRat has sources for his statements above? I'll note that the output of an antimatter bomb will (initially) consist of very high energy (~1 GeV) gamma rays, instead of the MeV gammas and hot plasma of a fission or fusion explosion; does someone know how efficiently that energy will couple into the bomb casing, or to adjacent air, earth, and buildings? My gut instinct is that for a ground burst of equivalant energy the appearance will be comparable (at any distance where an observer would live to tell about it), but I suspect there will be marked differences at very high altitude or in space (where escaping gamma rays won't be absorbed by surrounding matter). TenOfAllTrades(talk) 15:02, 23 April 2010 (UTC)

Shouldn't that 300 be 333 ? StuRat (talk) 15:13, 23 April 2010 (UTC)

It should be if you're making unreasonable assumptions about the precision o f the value 'about 0.3%', yes. Otherwise, no. TenOfAllTrades(talk) 16:23, 23 April 2010 (UTC)

According to Pastafarianism, will the universe be destroyed by equal amount of pasta and antipasta coming into contact with one another ? :-) StuRat (talk) 15:07, 23 April 2010 (UTC)

So does that mean that an antimatter bomb would have an effect for 10,000,000 kilometers in every direction, since the largest nuclear weapon caused destruction up to 1000 kilometers away? --71.144.122.18 (talk) 14:59, 23 April 2010 (UTC)

First of all, blast radius is not directly related to bomb energy yield. See blast radius. More often, yield energy is proportional to (blast radius)² or even in some cases, (blast radius)³. For the mathematically uninclined, this means that increasing the energy of the explosion will only increase the blast radius "a little bit." In fact, when modeling nuclear weapon yield, many practical, realistic estimates place the proportionality closer to E_yield = (blast radius)⁵: in other words, you need 100,000 times as much energy to generate a blast 10x as large (measured by spatial radius). More energy does mean more destruction in general, but the relationship defining "how much more" is very complicated. Nimur (talk) 15:21, 23 April 2010 (UTC)

No, not at all:

1) First, what nuclear weapon caused destruction 1000 km away ?

2) Let's use Ten's 300 times more powerful figure, since the maximum current bomb you refer to is likely a thermonuclear bomb, not a simple atomic bomb.

3) (See Nimur's comments above about blast radii.) StuRat (talk) 15:26, 23 April 2010 (UTC)

The Tsar Bomba makes claims that it broke windows and was felt 1000 km away, but those claims are uncited. The mesured zone of total destrucion was a much smaller 35 km radius. Googlemeister (talk) 15:45, 23 April 2010 (UTC)

Also note one practical effect of the diminishing returns from larger bombs is that many small bombs are far more destructive than one big bomb, where the total mass of explosives is equivalent. StuRat (talk) 15:57, 23 April 2010 (UTC)

So what would the blast radius be of an antimatter bomb with 500,000 kg of fuel (roughly 20 times Tsar Bomba)? Ignore the problems with building and dropping such a bomb, because this is for a sci-fi story which takes place far enough in the future that they've been solved. --71.144.122.18 (talk) 16:38, 23 April 2010 (UTC)

The bomb won't be 100% efficient as a lot of the energy will be lost in the form of neutrinos. Protons and anti-protons consist of quarks, so you get mesons when they decay. But then you can get mesons consisting of a quark and the anti partner of another type of quark. This will then decay into a muon and a neutrino. The energy lost in the form of neutrinos should be easy to estimate, the article on the antimatter bomb gives a figure of 60%.

Now, I think the effects of explosions should be universal in the sense that whenever you deposit a large amount of energy very quickly in some small volume, then the effects far away from that region should not strongly depend on the details of how that energy was deposited in a first approximation.

This then means that you can just as well use this calculator to compute the effects of an asteroid impact with the same kinetic energy. You should then, of course, disregard typical effects associated with impacts, like that of ejecta. But perhaps an underground explosion would be similar also in these respects. Count Iblis (talk) 17:14, 23 April 2010 (UTC)

For example, a 3*10^11 Megaton TNT explosion should cause the following effects at 10,000 km distance. The seismic effects should be:

The major seismic shaking will arrive at approximately 2000 seconds. Richter Scale Magnitude: 12.3 (This is greater than any earthquake in recorded history) Mercalli Scale Intensity at a distance of 10000 km:

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

The effects of the air blast should be:

The air blast will arrive at approximately 30300 seconds. Peak Overpressure: 295000 Pa = 2.95 bars = 41.9 psi Max wind velocity: 370 m/s = 828 mph Sound Intensity: 109 dB (May cause ear pain) Damage Description:

Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Glass windows will shatter.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

Count Iblis (talk) 17:29, 23 April 2010 (UTC)

If Iblis's math is correct on the amount of Mtons, then this blast would exceed the power of the Chicxulub crater impact that allegedly killed the dinosaurs by 3000x. Googlemeister (talk) 18:24, 23 April 2010 (UTC)

Just one small note. It's not correct that if a perfectly efficient antimatter bomb was possible, it would convert 100% of the mass of the antimatter into energy. The correct number is 200%, since an equal amount of normal matter would necessarily be converted. --Anonymous, 03:51 UTC, April 24, 2010.

Also, (unlike a nuclear fission/fusion bomb) it's certain that 100% of the antimatter will react with regular matter and be converted to energy - it's not like there could be antimatter 'left over' that could be scattered as fallout - as is the case with an atom bomb. So in that sense, it is 100% efficient. The issue is whether the resulting energy is emitted in ways considered useful for destruction of the target. That's where the difficulty lies. Also, a less-than-fully-efficient atomic bomb may actually cause you enemy more trouble because 'dirty fallout' that's still full of radioactive plutonium/uranium could easily kill more people and cause a larger area to be uninhabitable than a 'clean' bomb that would convert 100% of radioactive material into unreactive byproduct. SteveBaker (talk) 16:48, 24 April 2010 (UTC)

Like Steve just said , antimatter bobs are highly efficient when compared to modern day nuclear fusion/fission bomb.It would theoretically covert 100% of its mass into energy. This is theoretically true but if your look at it in a practical standpoint it will not release 100% of its energy.A extremely minute amount of antimatter may still remain.And to answer the original question ; Yes.An antimatter bomb would be immensely powerful when compared to a standard nuclear fission/fusion bomb as almost 100% of its matter is turned into energy.Modern nuclear fusion/fission bombs only covert a little of their mass to energy.This would potentially make antimatter bombs fallout free weapons .The intense radiation maybe bigger that anything we have seen, basically could sterilize anything in the blast radius

Penguins

How would the creationists today explain the flightless yet winged penguins? --Reticuli88 (talk) 14:44, 23 April 2010 (UTC)

I don't think that any explanation beyond "That's just the way God made it" is necessary for some people. --Jayron32 14:49, 23 April 2010 (UTC)

They use the wings to help them swim. --71.144.122.18 (talk) 14:52, 23 April 2010 (UTC)

Perhaps they evolved to survive The Deluge? Nimur (talk) 15:24, 23 April 2010 (UTC)

Maybe they would rather formulate it "God works in mysterious ways" if others try to point out seemingly illogical things. PrimeHunter (talk) 16:47, 23 April 2010 (UTC)

Or better yet "Who are you to question God ?", which implies that it's a sin to question God, and by extension God's representatives (the Church). StuRat (talk) 17:33, 23 April 2010 (UTC)

Us creationists take the easy way out of tough questions :)) Rimush (talk) 17:38, 23 April 2010 (UTC)

Penguin wings are anything but useless. They couldn't swim without them. --The High Fin Sperm Whale 18:21, 23 April 2010 (UTC)

See for example [2] and [3]. Gabbe (talk) 19:01, 23 April 2010 (UTC)

If you call the wings "flippers" then their construction makes pretty good sense from either point of view.APL (talk) 21:23, 23 April 2010 (UTC)

The whole problem here is that creationism is a pseudo-science. It claims the trappings of a science without following the scientific method (that's the definition of a pseudo-science). Because of that, creationists can just make up any story they like - they are (evidently) not required to provide proof of anything they say in order to keep their believers happy. Hence, asking these kinds of questions doesn't really allow you to prove or disprove anything whatever. SteveBaker (talk) 01:00, 24 April 2010 (UTC)

No explanation is necessary. I mean, their wings are used for balance, and for swimming. Just because they can't use them to lift off, it doesn't mean that they weren't invented by The Deity, or what have you. Besides, in the deadly Antarctic winter, having longer extremities is not good for your survival prospects. You want short little stubby wings so you don't lose copious amounts of body heat. Vranak (talk) 14:30, 24 April 2010 (UTC)

Well, that's not really true. Science can explain why penguins are birds - they evolved from other birds. They have wings because that's what birds have. They have evolved some features for survival in the extreme cold, others for swimming and so on...but (interestingly) they have not lost all of the features that birds evolved for flying (wings - and the huge chest muscles required to flap them). We can completely explain more or less every aspect of why a penguin is like a penguin is. The trouble for the ID "explanation" is to ask why penguins are like birds at all. Why don't they have propellers or water jet engines like a jet ski? The ID/creationism approach doesn't offer any degree of explanation whatever...the answer can only be "because the designer decided to do it that way". Since this designer produces some extraordinarily crappy designs sometimes - we have to wonder at his/her/its' sanity. I think an explanation is required - and the ability for science to provide one is a compelling thing. Why choose to believe a pseudoscience that can't explain a single fact about the nature of plants and animals beyond "well, just because the designer did it that way". That's a crappy system! I could understand choosing an "intelligent design" answer if there were no credible alternative - and that's why intelligent people believe in it hundreds of years ago when we had no better explanation. But now we have a really comprehensive, elegant explanation that fits all of the facts perfectly, choosing the ID/creationism answer is no more than pathetic dogmatism. SteveBaker (talk) 01:45, 25 April 2010 (UTC)

Creationists might point out that on board Noah's Ark there were two examples of every genus of bird. While Noah was waiting for some sign that the water had receded sufficiently to expose a few trees, all the birds remained in their cages on board. However, one breeding pair managed to sneak away! These were the first penguins! There were no trees to be seen so eventually they ended up in the water and had to keep swimming. They swam south and kept going until they reached the southern hemisphere (which is where the penguins live.) By the time they arrived in the southern hemisphere they were damn good swimmers and they never felt the need to fly again. And that is why there are penguins, to this very day. Dolphin (t) 11:32, 25 April 2010 (UTC)

That makes no sense whatever! Firstly, (as creationists are keen on pointing out) in their world view species most certainly don't change over time - they are created by god/the-designer and don't change from that point onwards. The idea that one pair of (presumably duck-like) birds swam so far and so long that they changed into penguins implies a kind of Lamarkism - it would be tantamount to agreeing with evolution! Most ID/creationist types don't deny that the form that plants and animals take is determined by their genes - they simply refuse to believe that those genes change over time. A few will grudgingly concede that genes may be lost over time - but none of them will agree that genes are ever added or improved over time - because that would require evolution. So I don't really see how creationists could logically subscribe to this view of how penguins came about (although anything is possible since logic is never their strong point). Furthermore, that kind of thing is easy to disprove - for example: A hundred generations of humans have learned to read - and practiced reading all their lives - yet not one child has ever been born with an innate ability to read. That kind of evidence is why Lamarkism is so out of favor these days. SteveBaker (talk) 18:47, 25 April 2010 (UTC)

Dolphin51's Noah's ark story is a joke. At least I hope it was meant as a joke, since it's not true. And BTW the Noah's ark is specifically considered as a miracle, and not something that could actually be made, so logical arguments about its existence are meaningless. Ariel. (talk) 05:46, 26 April 2010 (UTC)

Ariel is right. It was my attempt at humour. Dolphin (t) 11:34, 26 April 2010 (UTC)

These are the steps of the scientific method:

Ask a Question Do Background Research Construct a Hypothesis Test Your Hypothesis by Doing an Experiment Analyze Your Data and Draw a Conclusion Communicate Your Results

You cannot do an experiment to recreate life, whether you are a creationist or an evolutionist. This relegates the area of origins to the realm of philosophy. Neither creation nor evolution can be proved in a laboratory. The scientific method does not apply in this area. You would need to search for evidence to see which system gets the weight of proof.

Just a note: The story of Noah's Ark is true. Animals could have easily fit in the ark. The wood was durable, and the sealant would work well. It is not hard to build a covered raft, which is what Noah's Ark was. Animals that could have been too big to fit on the ark, such as dinosaurs, could have been led on when young.

Why did the penguin have to adapt to the cold Antarctic? They could have been created to be able to cope with extreme cold. Species could also undergo inbreeding. All of the birds which didn't have the proper genes would die in the cold, while the "freak" birds that had extra feathers survived and reproduced.

The complexity of life shows the presence of a Creator, not random scrambling of genes.

Where is the proof for evolution? Did someone reproduce it in a lab?

If anyone wants to make further comments on a creation/evolution discussion, feel free to use my talk page. --Cheminterest (talk) 21:21, 26 April 2010 (UTC)

Exoplanet naming scheme

Why do there seem to be two schemes of naming exoplanets? Science fiction has named planets "Name of star I", "Name of star II", "Name of star III"... for many decades now. Real exoplanets, however, are named "Name of star b", "Name of star c", "Name of star d"... Why is this? There has been a simple naming scheme for decades, so why was a new one invented instead? JIP | Talk 15:16, 23 April 2010 (UTC)

• Extra-solar planets from the Institute of Physics Reports on Progress in Physics (2000) has this to say: "Object names such as 70 Vir (for 70 Virginis) reflect standard astronomical (constellation-based) nomenclature, while other designations reflect discovery catalogues or techniques variously labelled with catalogue running numbers (e.g. HD 114762) or according to celestial coordinates (e.g. PSR 1257 + 12). The International Astronomical Union is in the process of formulating recommendations for the nomenclature of extra-solar planets (cf Warren and Dickel 1998), meanwhile the de facto custom denotes (multiple) planets around star X as X b, c, . . . , according to discovery sequence."
• Following the reference above, W.H. Warren, from the United States Naval Observatory / NASA Marshall Space Flight Center / Hughes STX, had this to say to the IAU General Assembly in 1997: Nomenclature for Extrasolar Substellar Objects: A New Challenge _{HTML version}. Primarily the issue lies in defining a unique and unambiguous way to refer to a specific object which is currently on the edge of detection. If somebody else detects "something else", which might actually be found later to be the same substellar object, we must find a way to ensure that two independent nomenclatures can somehow merge together.

Ultimately, the problem is one of consistency. We don't really know what we are looking at when we see a "stellar wobble," for example. Because extrasolar planets are on the current edge of detectability, we can't be certain of the parameters (including orbital distance, or even sequence number from the star, in the case of multi-planet extrasolar systems). So, to be sure that we refer to the same object, the name is determined by when it is first observed, rather than some parameter (like distance from its star). After significant scientific observation, we might find that (the hypothetical) α-Vir-a, discovered before (hypothetical) α-Vir-b and α-Vir-c, actually lies between those two in orbital radius. Nimur (talk) 15:50, 23 April 2010 (UTC)

Does this mean that extrasolar objects are, when they are first discovered, named with letters, and after they have been confirmed to be planets and their order is known, they get Roman numerals, but it's just that in real life, we have never actually got to the confirmation stage? If this is the case, then I can see the point. But why do the letters start with b? If it's to allow for a to be discovered later, why don't they start in the middle of the alphabet then? JIP | Talk 20:10, 23 April 2010 (UTC)

The method of naming planets with Roman numerals is contained only in science fiction. Even if the order were known for certain, the letter designation would still be used. As the convention of using Roman numerals preceded the discovery of the first extrasolar planets, we can see it as an attempted guess at future planetary nomenclature that, so far, has not panned out. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 20:37, 23 April 2010 (UTC)

I think in response to JIP's question about starting with b - this is because in some conventions, α-Vir-a refers to the star, in other words, to the "primary" at α-Vir. α-Vir-b therefore refers to the first substellar object (either an extrasolar planet, a brown dwarf, or some other "UFO") detected at the location of the α-Vir system. I agree that this nomenclature is not ideal. Nimur (talk) 22:23, 23 April 2010 (UTC)

The star already has a designation: α-Vir. Why make α-Vir-a mean the same thing? Or does α-Vir refer to the entire system? JIP | Talk 06:45, 24 April 2010 (UTC)

In binary systems (those that have two stars) that have only one designation like this, the two stars are givin capital letters so there's α-Virginis A and B. In this sense, the designation for the system is "α-Virginis" and that of the star is A, B, etc. I'm not sure why exoplanet nomenclature starts with b. It's possible that the scheme originally assumed that the principal body would be A/a and subsequent bodies would be B/b, C/c, but then we have examples like 16 Cygni Bb, 30 Arietis Bb, and HD 178911 Bb. BTW, "α-Virginis a" would be the designation of a planet orbiting both α-Virginis A and α-Virginis B (since that is a binary system) though I don't believe this kind of orbit has been detected yet. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 19:23, 24 April 2010 (UTC)

III

What does the (III) in something like Nickel(III) mean? —Preceding unsigned comment added by 76.230.229.37 (talk) 15:23, 23 April 2010 (UTC)

That is called the oxidation state, and is roughly derived from a simplified description of the number of electrons exchanged in the ionic bond. Nimur (talk) 15:26, 23 April 2010 (UTC)

In other words, it refers to a nickel atom with three less electrons than neutral nickel, or alternately a +3 oxidation state. Most metals have multiple oxidation states, so it is usually necessary to indicate which oxidation state a metal has in a particular compound (for example, to distinguish between a +2 charged nickel ion and a +3 charged nickel ion). The roman numeral is omitted in unambguous cases, which are basically group IA and IIA metals, and a few random other ones (Aluminum is always +3, Zinc is always +2, and silver is always +1, so we omit the roman numerals for those as well). Other than IA, IIA, Aluminum, Zinc, and Silver, you should always include the roman numeral beside the metal name in a compound to indicate which oxidation state the metal is in. --Jayron32 15:33, 23 April 2010 (UTC)

The use of Roman numerals in parentheses following a chemical element's name of symbol is part of Stock nomenclature, a naming system for chemical species.

Ben (talk) 15:45, 23 April 2010 (UTC)

When did chemistry textbooks used in high school switch from some other nomenclature (like prefixes to indicate oxidation state) to the Roman numerals? I seem to recall a different system. Edison (talk) 22:21, 23 April 2010 (UTC)

The older system used the "-ic" and "-ous" suffixes for the oxidation states. Thus, Cu¹⁺ = cuprous and Cu²⁺ = cupric. The problem with that system is that its relative to the element in question; so while Cu²⁺ = cupric, Fe²⁺ = ferrous (since Fe³⁺ = Ferric). So, you still can't tell from the name directly what the actual oxidation state is. However Copper(I) and Copper(II) are unambiguous. Plus, what do you do with an element like Manganese, which has at least 3 common oxidation states (2+, 4+, and 7+) and a slew of other less common, but documented ones. The roman numeral system is MUCH clearer. --Jayron32 00:45, 24 April 2010 (UTC)

IUPAC has been standardizing nomenclature and advocating for standardized chemistry education since around 1913 - but I can't find a definitive date for the introduction and mainstreaming of the roman-numeral system for inorganic compound names. Textbooks may have changed many years after recommendations were made. I learned both systems, and I strongly prefer the numeric system - the "ic"/"ous" system requires much more memorization. As far as elements with more than two oxidation states, there are additional prefixes: per- and hypo-, and there are also common names for certain compounds (for iron oxide, there is ferric and ferrous oxide, also known by common names, including wustite, hemtatite, magnetite, maghemite, and so on). This system reeks of the alchemic origin of chemistry - cryptic code-words and poorly-explained, vaguely latin-ish prefixes and suffixes to designate astrological significances loosely tied to the specific process for generating specific compounds. Nimur (talk) 06:03, 24 April 2010 (UTC)

So the old chemistry set bottles labelled "Cupric Sulphate" and "Ferric Ammonium Sulphate" would now be called what? Edison (talk) 03:28, 25 April 2010 (UTC)

Copper(II) sulfate and Ammonium iron(III) sulfate, respectively. Interestingly, both Cupric sulphate and Ferric ammonium sulfate (but not Ferric Ammonium sulphate) redirect to the correct articles. Buddy431 (talk) 05:27, 25 April 2010 (UTC)

Sulphate is used in Britain, while sulfate is used in America. Neither of them is wrong. --Cheminterest (talk) 21:24, 26 April 2010 (UTC)

Now there is a redirect from Ferric ammonium sulphate to the more pedestrian term. Edison (talk) 02:23, 27 April 2010 (UTC)

The basic assumptions of GR

The basic assumptions of GR are not clear. Steven Weinberg discussed this in his 1972 text. One assumption is nonlinearity. Imagine a satellite attracted to the earth and the sun. In Newtonian theory, the force on the satellite is the vector sum of the forces due to the earth and the sun. According to Weinberg, the force would contain a third term, the attraction to the gravitational fields of the sun and the earth. It is not clear how one calculates this force, nor has anyone tried to verify it. It is critical that we discuss basic assumptions. —Preceding unsigned comment added by Sanford123445 (talk • contribs) 18:14, 23 April 2010 (UTC)

I'm sorry, what is your question? Gabbe (talk) 18:51, 23 April 2010 (UTC)

In newtonian physics, gravity is considered instantaneous, and the force is directly toward the object. In relativity gravitational force moves at the speed of light, so the force is actually directed to where the object was, not necessarily where it is now. Frame-dragging can also cause the direction of gravitational force to be different from where newtonian physics expects. I hope I understood your question. Ariel. (talk) 22:49, 23 April 2010 (UTC)

Again and again and again, critics of GR describe gravity as a "force." In the context of GR, gravity is not a force. It is amazing that this simple point is so hard to grasp: in Einstein's General Relativity, GRAVITY IS NOT -- REPEAT IS NOT -- A "FORCE." Why is it so hard to assimilate this extremely simple, straightforward statement? Repeat after me: in GR, gravity is not a force.63.17.40.87 (talk) 02:38, 26 April 2010 (UTC)

Empty balloons

Ignoring the casing, how much extra buoyancy would a rigid balloon "filled" with a perfect vacuum give over, say, a hydrogen or helium balloon? And since I'm here, a follow-up question: Ignoring the prohibitive cost and availability issues, could you construct a buoyant "vacuum balloon" out of carbon nanotubes which would remain rigid against atmospheric pressure? GeeJo ^(t)⁄_(c) • 18:27, 23 April 2010 (UTC)

Looks like the density of helium is 0.2 g/L, and the density of air is 1.2 g/L. This means that helium is already around 85% as buoyant as vacuum. Hydrogen is around 0.1 g/L, which is even closer. Paul (Stansifer) 18:42, 23 April 2010 (UTC)

There have been a number of lengthy discussions here about this topic. here is one from 2006 and here is one from 2007. APL (talk) 19:19, 23 April 2010 (UTC)

And "ignoring the casing" completely changes things. If you count the casing, the extra buoyancy is totally negated by the container needed. It's difficult to even get a vacuum balloon that's lighter than air, much less lighter than a hydrogen balloon. StuRat (talk) 19:26, 23 April 2010 (UTC)

I asked myself this question once, many years ago. So, in different units:

1000 cubic feet of a vacuum has a lifting power of 80.7 lbs.

1000 cubic feet of hydrogen has a lifting power of 76 lbs.

1000 cubic feet of helium has a lifting power of 74 lbs.

The shell would have to therefore need weigh no more than 4,7 lbs. just to equal the lifting power of hydrogen. I came to the conclusion that using Carbon fiber-reinforced polymer (there was no such thing as nano-tubes back then) it would just be possible to construct a sphere of 1000 cubic feet displacement, with enough strength to withstand a mild vacuum. However, it would be very susceptible to suffering from sudden and catastrophic crushing if it was subjected to the slightest deformation. In other words: providing that the skin was in 'pure' compression -it would withstand atmospheric pressure. Larger spheres would of course displace a larger ratio of air for the given mass of carbon fibre skin. Yet the vulnerability of the skin to crumpling, makes any likelihood that this would be practical proposition outside of a laboratory very remote, to my mind at least. Carbon nano-tubes promise to be stronger and more ridged but I imagine that even hydrogen would be safer to use in any practical application. Also, because of the higher pressure differential present with a vacuum system, it would also lose buoyancy faster than hydrogen and helium. A helium dirigible takes a long time (days) to lose noticeable lift due to a puncture. I later had thought that it would be better to replace the air with water vapour. A slug of ²³⁸plutonium (plus lead shielding) would produce enough joules of heat to keep a large version of such a craft, aloft for years. Hey! and it would be immune to volcanic ash. --Aspro (talk) 19:56, 23 April 2010 (UTC)

Also, you said "mild vacuum", which I would take to mean a pressure lower than 1 atmosphere but significantly higher than 0. To get the extra bit of lifting power, you need something pretty close to a true vacuum or else you might just as well use hydrogen. --Anonymous, 03:55 UTC, April 24, 2010.

I just used the word 'mild' to indicate it was to the practical limitation one faces due to the plastic 'out-gassing' and I have no recollection now of what that was, nor what we could achieve with fibre bonding resins such as epoxy. The difference though, is a loss of lift which is a magnitude or more too small to bother about. Another problem that appears when trying to scale up to larger sizes, is that being under compression the skin will tend to resonate. This would be in the form of waves, with the direction of amplitude on radial axes. The number of waves dependant on the size and thickness of the skin(and air density, etc., etc.). Then there is the problem that greater air pressure at the bottom will tend to flatten the sphere at that end. This causes peek of higher stress around some of the resonance nodes. All this modelling convinced me, that the only application where these new materials have made a real contribution to mankind is than we can now buy some really good fishing rods.--Aspro (talk) 08:57, 24 April 2010 (UTC)

Number of mammals in the world

I was curious how many mammals there are in the world, not species, but individual citizens of my class, from the smallest infant bat to the largest blue whale. My estimates would put it in the billions, assuming that most mammalian species have less than a million members and there are at most 50 mammalian species as populous as us, but that's basically a guess.--Prosfilaes (talk) 18:53, 23 April 2010 (UTC)

I don't have a source, but I recall hearing that the mouse / rat is the most populous kind of mammal with ~200 billion individuals. Dragons flight (talk) 18:58, 23 April 2010 (UTC)

For the more common domestic mammals, there are 1.3 billion cows, 0.4 billion dogs, 2 billion pigs, and 1 billion sheep. As you can see, these numbers are totally swamped by small mammals like mice and rats. Googlemeister (talk) 19:04, 23 April 2010 (UTC)

 ! These sorts of numbers should not be proliferated without a source! Nimur (talk) 22:24, 23 April 2010 (UTC)

Laugh. I'm inclined to agree. Vranak (talk)

See Cattle, Dog, Pig, and Sheep. Googlemeister (talk) 13:47, 26 April 2010 (UTC)

Which is interesting, if a little problematic without a definition of which type of kind we're talking about. But given that, I'd guess I'm looking at under a trillion mammals, all told, unless there are way more squirrels and bats than I'd assume.--Prosfilaes (talk) 19:13, 23 April 2010 (UTC)

Oil Depth

How deep down and wide does an oil patch or field have to be to be considered worthwhile to drill? —Preceding unsigned comment added by 71.137.251.25 (talk) 19:40, 23 April 2010 (UTC)

That will depend on a lot of factors, so we can't give a very satisfactory numeric answer. Some considerations are; pressure of the oil in the well (higher pressure means less cost to get oil out), price oil is expected to fetch when production comes online (if you have a higher sale price, you can be less efficient), level of impurities in the oil (it costs money to get out stuff you don't want), viscosity of the oil (high viscosity needs to be heated for it to flow well), transport distance to refinery (cheaper to ship oil 5 miles then 500) and method of transport (pipeline, ship etc... cost different amounts). Costs are higher for offshore oil, and while a small patch might be worthwhile if it is 200 ft down, the same patch would not be worthwhile if it was 8,000 ft down, or under 2000 feet of water. Googlemeister (talk) 19:50, 23 April 2010 (UTC)

The ease with which the oil can be produced is crucial to the viability of an oil accumulation, this will depend on both the nature of the oil (light v. heavy) and the permeability of the rock that forms the reservoir. There have been very large oil discoveries that are unlikely ever to be produced due to poor reservoir permeability, such as the Ellida discovery offshore Norway, lots of excitement at the time [4] but no indication that it will ever be produced.[5] Mikenorton (talk) 21:45, 23 April 2010 (UTC)

Hydrocarbon exploration is the task of guessing how much oil is under the ground. Of course, it is almost always easier to get oil if it is shallow. If the oil flows to the surface, that's even better! If it's very deep underground, it's much more expensive to locate and extract it. So, a very complicated set of estimations takes place when somebody thinks they have found some oil, especially if it's very deep underground. Remember, we don't ever really know how much oil is underground until we drill it and extract it; and drilling costs money - so the whole process always boils down to "do we think there is enough oil to outweigh the cost of drilling?"

First, the location is determined as carefully as possible, using a combination of geology, stratigraphy, seismic imaging, exploration wells, and dumb luck. (The percentage of each ingredient varies from company to company, and region to region - in some parts of Saudi Arabia, you don't even really need to look, and wildcat wells, drilled at purely random locations by wealthy oilmen who enjoy casino roulette games, turn up wet often enough to be profitable). Other people do not like making financial decisions based on guess-work, so they prefer a scientifically-informed guess.

In geologically interesting parts of the world, like the Gulf of Mexico, the oil is very deep and far below the water and hidden underneath pesky salt diapirs. The probability of finding petroleum under 4 miles of seafloor below an 8000 foot deep ocean is very low, unless you know where to look. That is where the magic of seismic imaging comes in: using extremely low frequency sound waves, a sonic image of the rock layers is produced, and with a little geology and a lot of luck, you might be able to identify a reservoir. Next, a series of 3D models are designed to estimate how much fluid could possibly have been produced in that region, and the physics of the flow is modeled with very large computers. These extremely accurate numerical physics calculations that are basically giant "for-loops" modeling the fluid dynamics of the entire reservoir over many possible parameters; or focusing the seismic images; and so on. The software can take many months to run, meanwhile earning millions of dollars of profit for contract geophysical processing companies. When the programs are done, the results are plotted on to huge reels of paper (well, it's all digital now, but some still print out the seismic). Next, a geologist uses colored pencil on these printouts and draws the edges of where they believe the reservoir is. Then a numerical physicist computes a precision volume integral bounded by the color pencil sketch, and a petrophysicist multiplies this resulting volume by a porosity value and an extraction factor ("percentage efficiency" of getting oil out of the ground). We now know "how much oil is in the reservoir." If the fluid physics matches the seismic images, a businessman makes a risk analysis and decides whether the color-pencil drawings and the numerical calculations are probably correct. If they are all in order, things move on to the next step. Now the business man calls his economics team, who guess what the price of oil is going to be for the next few years. And the petroleum engineers look at the geophysical results and estimate what kind of expensive technology is needed to drill this prospect, and how quickly the oil can be brought out of the ground. An easy decision is made: if the total value of the volume of extractable oil, integrated over the production curve estimate for the next few years, will cost less than building the rig and operating the boats, then the well will be profitable. At this point, the businessman responsible for this prospect calls up his boss and asks to borrow the company's 600 million dollar drilling rig to float out to his new hydrocarbon prospect. If things go great, the physicists and geologists were right, the well is wet and oil and natural gas flow. If the contractors are lucky, nothing goes wrong and nobody dies in a horrible fiery explosion and the $600 million dollar rig doesn't sink, creating loss of life, an ecological catastrophe and an economic disaster, and everbody profits. Nimur (talk) 15:26, 24 April 2010 (UTC)

Of course, if the oil accumulation is too shallow, you may have to worry about biodegradation of the oil.

As a geologist, I'd just like to point out that I've only used my coloured pencils twice in the last ten years, I spend my days sat in front of a computer workstation where I look at, and interpret the seismic images using specialist software that's been around for more than 20 years. Mikenorton (talk) 15:40, 24 April 2010 (UTC)

I admit it was an unfair jab at the geologists; really I intended to point out the ironic juxtaposition of extremely accurate and extremely inaccurate techniques in the estimation of geologic and economic risk parameters. Everybody, including the physicists, engineers, and economists, have a few "color pencils" in their toolbox to draw over the uncertain estimates. Nimur (talk) 15:46, 24 April 2010 (UTC)

That's OK, I've worked with lots of geophysicists over the years, some of them have difficulty coping with the often enormous uncertainty involved in the geological model, whereas geologists are used to that sort of thing - I was once asked to estimate the age of the formation at the bottom of a proposed well and I replied "definitely Phanerozoic", meaning that I wasn't even sure whether it would be Mesozoic or Paleozoic, but that's just how it is sometimes in frontier exploration. Mikenorton (talk) 15:56, 24 April 2010 (UTC)

GLYCOLYSIS video(s) in µm/Å-scale

Ok, I'm just learning about GLYCOLYSIS today. I'm watching many of the 10 Step Processes done in excellent 3D graphs and chartworks. My question, and note, I don't know a thing about Microscopy. Just naming off some randoms here: Transmission Electron Microscopy Area (TEM), or Positron emission tomography (PET). These types or others, do we even have the capability to watch the 10 Steps of Glycolysis, and/or just basic MitochondriaWorks with Microscopy/Video? If I'm doing video searches, if there are such videos, what to type on me search? Cheers, --i am the kwisatz haderach (talk) 19:57, 23 April 2010 (UTC)

an example of what kind of videos I'm looking for is this youtube vid done on CELL BIOLOGY by:phoenixfilmandvideo. It was made back in 1981, and has a very Cecile B. Demille 10 Commandments-like Narrator. It's chunking together basic Cell Biology infos in just 17 mins. The Microscopy parts, he just skims over. I'm looking for videos where it breaks down each segment, with way smaller in there. Even if not on the Nets, do you have an suggestions on pretty good Biology DVD's with MUCHO-MUCHO ELECTRON MICROSCOPY FEEDS? --i am the kwisatz haderach (talk) 22:39, 23 April 2010 (UTC)

What's the point in some reflexes?

I can see how some reflexes e.g. how the pupils react to changes in light are beneficial to us. But others, I can't see how they would convey any evolutionary advantage at all! For example the knee jerk reflex, the brachioradialis reflex... how can reflexes such as these help our survival? Thanks RichYPE (talk) 20:15, 23 April 2010 (UTC)

I believe they're side-effects of other, more useful reflexes. For instance the knee-jerk reflex is part of the feedback loop that helps us stand upright without consciously worrying about balance. Unfortunately, The Patellar reflex article only dedicates about a sentence and a half to this. APL (talk) 21:14, 23 April 2010 (UTC)

As I understand it, the knee-jerk reflex triggers naturally every time you take a step, causing your lower leg to extend and therefore exert a force to support your weight. It is an essential part of walking. This doesn't mean that every reflex has a function, though -- some might be relics of evolutionary history. Looie496 (talk) 23:25, 23 April 2010 (UTC)

Hi guys thanks for your responses, are there any sources you can cite as I would like to look into this further. Thanks RichYPE (talk) 15:45, 24 April 2010 (UTC)

I would say that all reflexes are protective by definition as they are instinctive in a physiologic way. The knee-jerk reflex is a just a great example of a reflex that has been misappropriated by the nomenclature, in that we call it a knee-jerk because of the way in which it as a reflex, as representative of all or most reflexes are working in the body. But if you're standing against a wall and you doze off and your knees buckle, your quadriceps is extended by the pulling motion of the tendon over the knee area and your Golgi tendon organ is activated by this tension. It then sends a message for your quadriceps to flex, thereby re-establishing equilibrium. DRosenbach ^{(Talk | Contribs)} 02:24, 25 April 2010 (UTC)

Most reflexes have a use, even though they might not be fully understood.--Cheminterest (talk) 21:26, 26 April 2010 (UTC)

Abdomen

Is there a term for the area of abdomen between the belly button and the groin? (ie the bit that hangs below your belt)--79.76.130.158 (talk) 21:27, 23 April 2010 (UTC)

Left lower quadrant (abdomen) or right lower quadrant (abdomen)? ~AH1^(TCU) 21:33, 23 April 2010 (UTC)

The supra pubic area? —Preceding unsigned comment added by 86.4.186.107 (talk) 21:52, 23 April 2010 (UTC)

Wait, you wear your belt around your belly button? I thought belts were worn just over the hips. —Preceding unsigned comment added by 99.254.8.208 (talk) 22:24, 23 April 2010 (UTC)

MY wife and I have this debate. I wear my pants around my hips, and her waistband crosses her belly button. Its apparently not a settled matter... --Jayron32 00:31, 24 April 2010 (UTC)

Hypogastrium --Arcadian (talk) 00:40, 24 April 2010 (UTC)

Ok then, what is the reason for protruding hypogastrium in older women, when they are not necessarily fat?--79.76.130.158 (talk) 11:28, 24 April 2010 (UTC)

Poor tone of abd muscles, esp from previous stretching during pregnancy. It's called a paunch. Also fat, even when limbs are not obviously fat. alteripse (talk) 11:34, 24 April 2010 (UTC)

Ok how can this tone be improved? Sit ups?--79.76.130.158 (talk) 12:52, 24 April 2010 (UTC)

Yes, though crunches may be better. See also leg raise. Abdominoplasty (surgical procedure) is also a rather drastic possibility. --220.101.28.25 (talk) 18:53, 24 April 2010 (UTC)

scuba

how long air will a scuba tank give u? and what compression is used on it? —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:13, 23 April 2010 (UTC)

Diving_cylinder#Breathing_Time --Aspro (talk) 22:24, 23 April 2010 (UTC)

Note that your dive time is usually limited not by the air in your tank, but by your careful adherence to the dive tables or to your dive computer; you have to come up before decompression sickness becomes inevitable. Here is a long FAQ about tank filling, with a little picture of their fill station, and lot of information for technical diving. Comet Tuttle (talk) 22:38, 23 April 2010 (UTC)

The pressure is about 2,900 to 4,400 psi. Ariel. (talk) 22:53, 23 April 2010 (UTC)

The OP seem to be asking for a ball park sort of generalisation. Since a lot of people never get beyond trashing around ( a technical term for a certain swimming style) in depths of no more than 30 feet, for some 20 minutes at a time, on a 70 l tank. Adherence to decompress times is unlikely to take up much time at all. Beyond this however, it is as Comet Tuttle above points out – a more complex question.--Aspro (talk) 23:00, 23 April 2010 (UTC)

yes i just need a generalization. i heard that but it might be hard to control the flow of 2000 PSI tank? does it use a flow regulator? —Preceding unsigned comment added by Tom12350 (talk • contribs) 00:00, 24 April 2010 (UTC)

SCUBA specifically refers to the combination of a pressurized tank and a diving regulator. I have seen an instructor breathe out of an unregulated cylinder by carefully cracking the valve (which is stupid and dangerous). If you dive to shallow depths (where the fun stuff is, anyway), you can get as much as 40 minutes or an hour out of a 3000 psi tank. Your breathe-rate varies by at least a factor of two based on how calm and controlled you are - inexperienced divers waste air and run out long before they otherwise would. At greater depths, you typically consume air faster (because the regulated pressure is higher); but this also depends on controlled breathing. It is possible, but dangerous, to breathe less often when you are breathing high pressure air - your oxygen partial pressure is higher and you can "survive" longer off of each breath; this extends the down-time, but contributes to a variety of hazardous conditions, including decompression sickness. If you need more down-time, technical divers carry multiple bottles and/or use other gas mixes. As has been pointed out, in most deep dives, the limiting factor is not quantity of air, but safety due to compression hazard and nitrogen narcosis, oxygen toxicity, and decompression sickness. Nimur (talk) 01:52, 24 April 2010 (UTC)

The person at the lower right just breathed out.

where does the air you breathe out go? also why is it dangerous to breathe out of a unregulated cylinder ?

To question 1: It depends on whether or not you are using a rebreather or an open-circuit Scuba set. Rebreathers trap exhaled gas, while in open-circuit systems your exhaled breath just bubbles away. And breathing from an unregulated cylinder is very dangerous because it is unregulated. A sudden burst of high-pressure air into your head can cause all sorts of damage to your lungs and breathing system. Having your lungs pop like a balloon because you opened the valve on the cylinder too far doesn't sound like a good idea. Also consider the Newton's third law of motion problems with opening the valve too far. Doesn't sound like fun to me... --Jayron32 04:36, 24 April 2010 (UTC)

Of course our article Scuba diving will be of interest. Comet Tuttle (talk) 06:33, 24 April 2010 (UTC)

how does the air "just bubble away. " is there an exit valve? what about on the scuba fireman where?

The mouthpiece has a second set of valves, including a demand valve and a backpressure valve. The diagrams in our article illustrate how complicated all of this is - but basically, the air is delivered at the correct pressure when you breathe in; and when you breathe out, those valves close and your exhaled air blows out an outlet valve and bubbles into the water. The design of all of these valves is necessarily complicated to make sure that both the correct pressure is delivered, and that water is unable to flow into the mouth or the air tank. Nimur (talk) 22:46, 24 April 2010 (UTC)

The 'U' in 'SCUBA' stands for "underwater" (Self Contained Underwater Breathing Apparatus) - so the things that firemen wear isn't SCUBA gear. SteveBaker (talk) 01:21, 25 April 2010 (UTC)

muscle fuel

I can start walking any time I want, so there must be some sort of fuel stored in each individual muscle cell, ready to be used any time. I can keep walking for hours at a time, or I can run for ten minutes, before I have to stop. Did the muscle cells start with enough fuel in each one to work for that long, or are they being refuelled through the blood while I'm walking? If they are being refuelled, is there a fuel storage area in my body where I keep the extra fuel after digesting it but before distributing it to a cell? —Preceding unsigned comment added by 99.254.8.208 (talk) 22:18, 23 April 2010 (UTC)

Now that's a good question. Look at Glycogen and Mitochondrion.--Aspro (talk) 22:32, 23 April 2010 (UTC)

Aerobic vs. anaerobic exercise may be helpful as well. Short runs are typically anaerobic sprinting, while long, endured exercise is more commonly aerobic. These are qualitatively different metabolic processes and utilize different biochemistry to release energy. Nimur (talk) 01:55, 24 April 2010 (UTC)

THe only usable form of energy is adenosine triphosphate. Glycogen and glucose only form and reform the hydrogen bond between the last two phosphate ions. 99.13.216.93 (talk) 02:34, 24 April 2010 (UTC)

True, but ATP is the last step in many long processes which produce energy for cells. Its like saying that your lights come on because you flip the switch on the wall, and then ignore the process that got the energy to the switch. ATP is the ultimate source of energy for cells, but the role of substances like Glucose and Glycogen in the transport and storage of energy cannot and should not be understated. --Jayron32 03:17, 24 April 2010 (UTC)

The fuel is glycogen and it's stored in your muscles and liver. So in that case, the fuel storage area will be the liver. Your body refuels its glycogen reserves by converting stored fat in the body. --41.177.6.108 (talk) 09:31, 24 April 2010 (UTC)

Fat is not to any significant extent converted to glucose (which is a necessary intermediate for making glycogen). See Glyconeogenesis, especially the section Entering the pathway. The glycerol part of triglycerides can be converted to glucose, but the fatty acids cannot. --NorwegianBlue ^talk 10:12, 24 April 2010 (UTC)

Yet it seems I can exhaust the supply in the muscles and liver by jogging for an hour, and some refuelling in the form of juice or other sugar is needed for continued exertion. Is it like a car with a very small gas tank? Edison (talk) 03:32, 25 April 2010 (UTC)

I believe your observation is due to the following effect: Fatty acids are broken down through beta oxidation to the two-carbon acetyl-group (in the form of acetyl-CoA), which combines with oxaloacetate, as the first step of the citric acid cycle. Oxaloacetate and the other intermediates of the citric acid cycle are not consumed in the cycle itself, but may be used as fuel through other biochemical pathways. During prolonged excercise, the level of citric acid cycle intermediates decreases (see), leading to less efficient oxidation of acetyl-CoA, and therefore less efficient usage of fat as fuel. Intake of carbohydrates will lead to production of citric acid cycle intermediates, and again allow you to burn fat more efficiently. There may be a bit of OR/speculation in the above, I would have liked to have sourced it better. --NorwegianBlue ^talk 10:49, 25 April 2010 (UTC)

April 24

Energy used in travel

How many joules of energy are expended by each of the following 16 entities? (Additional details for each of the 16 entities: Please deal with entity variations by providing minimum and medium and maximum values; or please specify a typical specimen and provide a value for that specimen. Please assume that there is no wind in the air and no current in the water.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)
[I am inserting the underlined text. -- Wavelength (talk) 03:34, 24 April 2010 (UTC)]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.. --Jayron32 03:34, 24 April 2010 (UTC)

None of these questions is a homework question. I am simply curious about all of them. -- Wavelength (talk) 03:39, 24 April 2010 (UTC)

In that case, these are insansely complex problems anyways. The work done by each body in traveling one kilometer. Its a rather complicated problem, since in a perfect frictionless system, the work = 0 if the movement is at a constant velocity. So the work done in traveling one kilometer is the work done overcoming friction. These systems are fantasticly complex; you could calculate joules of energy consumed in traveling that distance for some of these. For example, given a car with a fuel efficiency of 30 km/gallon of gasoline you could calculate the mass of gasoline burned and then the joules of heat released in burning that gasoline from the Heat of combustion value for gasoline. For the human examples, there are ways of calculating "food energy" consumed per minute for various activities, but these are usually pretty inaccurate measurements. Still, you can find calculators online that will do this for you. Then you just need to convert from food calories to joules. --Jayron32 03:49, 24 April 2010 (UTC)

Remember that in both air and water, drag is really important as speed increases (drag increases with the square of the speed). So the speed needs to be known for all the mechanical systems. There are also questions of efficiency. Some engines are more efficient at high speed -- airplane engines are more efficient at the low temperatures of high altitude. The air is also much thinner there. At 1 km altitude, air friction would be quite high and the engines not as good. An aircraft blog I visited earlier gave an economy of ~2.7L/100km/passenger for a Boeing 777-300ER and ~3.1L/100km/passenger for an Airbus A330 and that's overall with most of the flight at ~10km altitude and Mach 0.82 or so (see comment 9 here). -- Flyguy649 ^talk 04:28, 24 April 2010 (UTC)

Also, another difficulty is that airplanes weigh anywhere from a couple hundred pounds to over a million pounds. The An-225 would use an absolutely incredible amount more energy than the CriCri, and the engines are optimized for completely different altitudes. The same (in terms of the weight) goes with automobiles (though not as extreme) and the other things you mention. Even amongst airliners, there will often be a significant difference between types. Falconus^{p t c} 05:02, 24 April 2010 (UTC)

My clarification about "entity variations" applies to all those variations. -- Wavelength (talk) 21:31, 24 April 2010 (UTC)

Extended content

Energy used in travel: by a man walking How many joules of energy are expended by a man walking along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man running How many joules of energy are expended by a man running along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man bicycling How many joules of energy are expended by a man bicycling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man swimming How many joules of energy are expended by a man swimming along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man pedaling a pedal boat How many joules of energy are expended by a man pedaling a pedal boat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man rowing a rowboat How many joules of energy are expended by a man pedaling a rowboat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a rider How many joules of energy are expended by a horse carrying a rider along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a carriage How many joules of energy are expended by a horse pulling a carriage along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a motorcycle How many joules of energy are expended by a motorcycle traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an automobile How many joules of energy are expended by an automobile traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a bus (omnibus) How many joules of energy are expended by a bus traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a ferryboat How many joules of energy are expended by a ferryboat traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a steam locomotive How many joules of energy are expended by a steam locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a diesel locomotive How many joules of energy are expended by a diesel locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an airplane (aeroplane) How many joules of energy are expended by an airplane flying along a distance of one kilometer in a straight line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a helicopter How many joules of energy are expended by a helicopter flying along a distance of one kilometer in a straight and horizontal line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)

16 questions from Wavelength collapsed, all identical except for the vehicle. Comet Tuttle (talk) 06:30, 24 April 2010 (UTC)

Could they please be removed? They're screwing up the Table of Contents 82.43.89.71 (talk) 23:41, 24 April 2010 (UTC)

They were not a problem to the Table of Contents until they were collapsed in a recent revision. If they are removed, the discussion will be hanging without the complete context. If the collapsing is not going to be undone, the main heading can be reworded to say "Energy used in travel (collapsed subheadings non-functional in links)", that is to say, including the links in the Table of Contents. But However, I prefer that the collapsing be undone. -- Wavelength (talk) 05:45, 25 April 2010 (UTC)

[I am revising my post of 05:45, 25 April 2010 (UTC). -- Wavelength (talk) 15:31, 26 April 2010 (UTC)]

Are you sure this is what 82.43 is referring to? My guess is the complaint is about the very large TOC due to the 16 additional items (that's aboutmore then the average, and possibly median, of a whole days worth), not the inability to navigate to the individual sub-questions; and that problem occured both before and after the collapsing Nil Einne (talk) 06:35, 25 April 2010 (UTC)

See Bicycle_performance#Energy_efficiency for figures for three of the above. 89.243.216.99 (talk) 13:11, 25 April 2010 (UTC)

You'll be able to find some details for cars, planes etc in Part I of Without Hot Air by David MacKay. 131.111.30.21 (talk) 16:14, 26 April 2010 (UTC)

Thank you, 89.243.216.99 and 131.111.30.21, for your replies and those links. -- Wavelength (talk) 22:10, 26 April 2010 (UTC)

Why no plastic beer bottles?

Why do I never see beer in plastic bottles sold anywhere? Why are they either in aluminum or glass? --70.179.176.30 (talk) 04:09, 24 April 2010 (UTC)

Beer is often sold in plastic bottles at punk/skinhead/metal/etc. gigs. It hurts the singers and band members less when people hurl the bottles at their heads. Also makes it harder to use bottles as weapons when the crowd start beating on each other. :) --Kurt Shaped Box (talk) 04:20, 24 April 2010 (UTC)

(edit conflict) Well, not demonstratably true. For over a decade Anheuser-Busch has sold beer in plastic bottles, and they weren't the first, Miller started some time before they did. Plastic bottles are not as popular as beer sold in cans or glass, tradition being what it is, but they certainly exist. You see them a lot more at major events like ball games or rock concerts, where glass is a concern for safety reasons. However, you can find them in grocery stores and other places where you can buy beer. --Jayron32 04:22, 24 April 2010 (UTC)

I'm pretty sure that I've bought plastic 500ml bottles of Bud in England before, FWIW. --Kurt Shaped Box (talk) 04:29, 24 April 2010 (UTC)

Aye, well, most bottled water is sold in plastic. :) --KägeTorä - (影虎) (TALK) 18:18, 24 April 2010 (UTC)

http://www.packaging-gateway.com/features/feature79/ has some comparisons and consumer info. You can do your own research with Google on beer plastic bottles. PrimeHunter (talk) 04:38, 24 April 2010 (UTC)

Interesting link — it seems to claim the major reason is that more oxygen gets into the bottle while it's on the shelf; but I thought plastic was airtight, and don't particularly see why the cap on a plastic bottle would let in more oxygen than the cap on a glass bottle. Comet Tuttle (talk) 06:28, 24 April 2010 (UTC)

Interesting enough, it also mentions cost. I presume this is in comparison to aluminium cans rather then glass bottles but don't really know. This [6] mentions cost as a factor in 2001. As an aside, plastic bottles are common in stadiums as has been mentioned, but while not as dangerous as glass, they still pose a threat, particularly of course when full and sealed. Stadiums sometimes limit bottle size (even for brought in bottles) as a result. Similarly, tap beer with paper or plastic cups for the beer [7] Nil Einne (talk) 07:24, 24 April 2010 (UTC)

The plastic is not airtight! The plastic allows diffusion of gas, depending on the exact material this diffusion is varying. The oxygen diffuses into the beer and changes the taste by oxidation reactions. There are certain surface treatments necessary for beer bottle to lower this diffusion. There is a book about the properties of polymers which has a good introduction [8] --Stone (talk) 08:12, 24 April 2010 (UTC)

For me, drinking beer from a plastic bottle would be like drinking water from a muddy puddle. It's just not preferred, when inert glass is available. Vranak (talk) 14:25, 24 April 2010 (UTC)

Glass and aluminium cans are much more recyclable than plastic - going to plastic bottles would be a retrograde step. SteveBaker (talk) 18:04, 24 April 2010 (UTC)

To me the Q shouldn't be why beer isn't commonly sold in plastic bottles, but why soda-pop is. It goes flat much faster in plastic, because the plastic isn't airtight, and the bottle may also leach chemicals out of the plastic, into the contents. StuRat (talk) 18:18, 24 April 2010 (UTC)

Similar question: Why in the US is water not sold in 2 liter bottles? This came as a shock to me when I tried to buy it, and had to settle for two 1 liters. Staecker (talk) 22:43, 24 April 2010 (UTC)

Because it comes in gallons. Like milk. How it's decided what is sold in gallons and what is sold in liters is one of the great mysteries of life.

Of course ...while I can understand a single serving, it feels pretty crazy to buy an entire gallon of tap water that someone has put into a bottle. I get that stuff literally piped into my house! APL (talk) 03:15, 25 April 2010 (UTC)

I suspect that the answer is that US manufacturers tend to stick with traditional units (ounces, pints, quarts, and gallons; in this case), until they reduce the size and want to hide this fact from consumers. Then they switch to metric to maximize deception and confusion. This happened with car engines, where a muscle car engine went from 455/460 cubic inches to 5.7 L, so nobody would notice that it was now 3/4 as big. This prevented consumers from trying to pay 3/4 as much. I wonder if any company has then done the reverse, and switched back to traditional units, when they next need to deceive consumers about another decrease in size. StuRat (talk) 07:18, 25 April 2010 (UTC)

Well it's easy to buy 1 liter of water (or soda), even though this is slightly more than a quart. Staecker (talk) 11:59, 25 April 2010 (UTC)

But were the previous bottles a quart (32 ounces), or maybe 36 ounces, slightly larger than a liter ? StuRat (talk) 15:00, 25 April 2010 (UTC)

Catabolic breakdown of muscles

Hello. I've heard many a bodybuilder say that catabolism starts breaking down muscles after about six hours of fasting. However, it seems quite exaggerated to me, so I've come here to seek a scientific answer. For an average person, how much time without eating does it take for the body to start breaking down muscles noticeably to feed itself?

(By "noticeably", I mean to the point that the bodybuilder may lose the muscle mass he has gained by working out during the day, or more). Thank you guys! --95.120.13.224 (talk) 08:35, 24 April 2010 (UTC)

Since they aim to get their fat to muscle ratio to the minim I expect their energy reserves are low. This is an area that the military have long been interested in, maybe another wikipedian knows of a good s reference. You might find of interest some of the things gone into on this site [9]. Fasting adds a complication because metabolism tends to slow down under these conditions.--Aspro (talk) 09:39, 24 April 2010 (UTC)

We may simplify anabolic/catabolic relationships as follows (for an average adult): 1. For about 3-4 hours after a mixed meal, glucose and amino acids and free fatty acids are coming from the gut into the blood; insulin levels are high and glucose is actively moved into liver, kidneys, and muscle, where it is stored as glycogen in all three, and amino acids are moved into muscles and incorporated into protein. From about 4 to 16 hours after a meal, insulin levels fall gradually, and blood glucose levels are maintained by glycogenolysis from liver and kidneys (not muscle), and there is little net uptake or output of amino acids from the muscle. By 16 hours (with wide variation), liver and kidney glycogen is depleted (not entirely gone) and insulin levels are low enough to allow catabolism of both fat and muscle for purposes of making glucose by gluconeogenesis. This is also when ketogenesis from fat breakdown begins. See Cori cycle. This is somewhat oversimplified, as there is considerable overlap between end of glycogenolysis and start of gluconeogenesis, but perhaps is a useful way to think about it for clinical and physical culture purposes. alteripse (talk) 11:13, 24 April 2010 (UTC)

It seems to me that the time frame would change dramatically based on activity levels, with each step taking far longer when asleep than while running a marathon. So, what activity levels were assumed for those values, Alterprise ? Also, doesn't the nature of the last meal matter, with sugars being digested far quicker than fats ? StuRat (talk) 11:19, 24 April 2010 (UTC)

Overnight resting. The major fuel source for muscle activity is muscle glycogen, which is used in muscles during exercise, and not for ordinary between-meal blood glucose maintenance. This partial separation reduces the exercise effect on whole body metabolic balance but amplifies it for in-muscle glycogen balance. Speed of digestion has an early effect which is why I specified mixed meal, but has little effect on the timing of the later stages. We use cornstarch to prolong digestible glucose intake in people whose glycogenolysis and gluconeogenesis is defective but it only adds a couple hours at best. So does a huge high fat meal. alteripse (talk) 11:27, 24 April 2010 (UTC)

Number of cells in a human body

How many (approximately) cells are there in a (an average, adult) human? RJFJR (talk) 13:10, 24 April 2010 (UTC)

Close to 50 trillion cells. However, that conflicts with Human_flora#Gut_flora which declares it to be about 10 trillion cells and Cell (biology) at a 100 trillion. Is this assuming a standard human of 70 kg I wonder? Looks like we will have to do a little proof correcting on these articles. --Aspro (talk) 13:38, 24 April 2010 (UTC)

Do you mean total number of cells, or number of Human cells? I've read somewhere (sorry, no reference yet) that the number of non-human cells (for example, bacteria in the gut and on the skin) out-number the cells that actually have your own human DNA.24.150.18.30 (talk) 15:11, 24 April 2010 (UTC)

The OP's word "in" an average human must include gut flora. Cuddlyable3 (talk) 15:39, 24 April 2010 (UTC)

And do we include dead cells ? A good portion of the skin is dead, so that makes a diff. StuRat (talk) 15:20, 24 April 2010 (UTC)

This must be a harder thing to estimate than it at first appears, as I can't find any references to this in my human physiology text books nor on any of the human genome sites, etc. To give the OP a figure could we say: The average human adult is composed of cells numbering between the magnitude of 1 x 10^13 and 1 x 10 ^14. --Aspro (talk) 16:10, 24 April 2010 (UTC)

Well, Human_flora#Gut_flora and Cell (biology) are compatible, as there are indeed roughly 10 times more non-human than human cells in a human. So Cell (biology) apparently counts all the cells that are inside a person. --Stephan Schulz (talk) 20:06, 24 April 2010 (UTC)

What is strange here is that humans are colonies of cells. So, you have intelligent colonies of cells that have difficulties estimating how many cells they themselves consist of :) . Count Iblis (talk) 20:46, 24 April 2010 (UTC)

Katla

Hi. If Katla were to erupt, how much water vapor would be released into the atmosphere and how much sea level rise would occur from the melted glacier (I previously calculated a figure of 0.3 mm)? Considering both the vapor released into the troposphere and stratosphere, what would be its equivalent CO₂e warming effect as an increase in equivalent carbon dioxide concentrations in ppm? Finally, would the net result from the combination of the ash, sulfur, and vapor ejected from the volcano produce net warming or cooling of the Earth globally in terms of surface temperature, or is this indeterminate? Thanks. ~AH1^(TCU) 13:43, 24 April 2010 (UTC)

I believe volcanoes typically cool the Earth, since the additional sunlight and heat reflected back into space from the ash clouds outweigh all the other factors. StuRat (talk) 15:17, 24 April 2010 (UTC)

I agree. To get a significant warming effect, you need to have an enormous eruption in which huge quantities of CO2 are emitted. Then, because of the long atmospheric lifetime of CO2 (far longer than that of the dust and aerosols), you can get a warming effect. Note that H20 only has a short atmosheric lifetime. I think that even supervolcano eruptions are not large enough; they will still produce a net cooling effect. But large flood basalt eruptions, such as the one that formed the Siberian Traps, will lead to a net warming effect. Count Iblis (talk) 15:52, 24 April 2010 (UTC)

CO2 lives in the upper atmosphere for thousands of years. So I'd expect there to be a short-term cooling effect due to the light colored clouds produced by the volcano - but that effect can't last for more than a year - so the longer term effect can only be to contribute to global warming. SteveBaker (talk) 01:15, 25 April 2010 (UTC)

Stratified Italian soda + cold cream => Salt fingers??

A fluid mechanics professor and myself are a bit stumped on this question:

Go to your local cafe, order an Italian soda. Make sure the barista/server pours the soda in very gently so that the syrup & soda remain as stratified as possible. Now get the carafe of cold half & half & pour in 1-2 tablespoons. The cream is significantly denser than the soda and sinks quickly. However, the syrup is denser than the cream and so the cream is stopped abruptly at the syrup/soda interface. (Side note: the breakdown of large -> small turbulent structures at this point is really cool!)

After ~10 seconds, small fingers of cream appear to drop into the syrup layer ... and look a LOT like salt fingers (see wiki article + links on those). Salt finger theory relies on the lower layer being cold and the upper layer being warm such that thermal diffusivity causes displacement instability (i.e. a bit of warm upper fluid is randomly displaced downward, quickly loses its heat to the ambient cold layer, and continues to fall downward because its density just increased through loss of heat).

In the case of the Italian soda, the cream (upper layer) is COLD and the syrup (lower layer) is warm/room temperature. This SHOULD be a STABLE configuration provided that the syrup is indeed denser than the cream, because any parcel of fluid that falls into the syrup should get warmer, lose density, and rise back to the point of equilibrium. Yet these fingers clearly fall into the syrup.

I thus present this conundrum to the reference desk. I highly recommend you try it!

128.193.45.125 (talk) 20:46, 24 April 2010 (UTC)

I'm afraid I haven't been able to get you a complete answer. Poking around the web, I find these figures for the specific gravity (density) of

• Half and half: 1.031 g/cc at 4.4°C, and 1.024 g/cc at 20.0°C;
• Pure water: 1.000 g/cc at 4°C, and 0.998 g/cc at 20°C;
• The densities for the flavor syrups will depend on the manufacturer and the particular syrup. For Torani brand, there appears to be between 15 and 23 grams of sugar per 30 mL (1 fluid ounce) serving; you'll have to find the tabulated densities for sucrose solutions (the primary contribution to the sugars is cane sugar: sucrose.

Hopefully you'll find what you're looking for. TenOfAllTrades(talk) 21:30, 24 April 2010 (UTC)

Here's my guess: the syrup curdles the cream, creating globules (curds) that are denser and therefore fall into the syrup until the density finds an appropriate equilibrium. Any chemists out there know if syrups are acidic enough to do this?128.193.45.125 (talk) 22:11, 24 April 2010 (UTC)

You might be right - but I suppose there is another possibility. I suspect that the syrup and the cream are very similar in density - with the cream being very slightly the denser. As the cream descends through the liquid, the density gradient will reduce the downward force on the cream to the point where there isn't enough density difference to provide a force that will overcome the viscosity of the liquid. Hence, I'd expect the cream to stop moving just before it's at the right density level. What we have now is a slightly unstable situation - but without enough energy in the overall liquid to overcome the viscosity barrier. But there is still small-scale random motion going on - so it's only a matter of time when two or three streams of liquid flow that happen to be heading in the same direction join and together provide enough energy to overcome the viscosity of the syrup. Hence, the cream breaks through in these "fingers" that appear more or less at random. Once they get started, they can be self-sustaining and will eventually allow the cream to flow to the very bottom.

It would be interesting to get an accurate measure of the densities of syrup and cream...but because either can absorb water and other 'stuff' in this complex mixture, it may be that they absorb other parts of the liquid at different rates. Any system as complex as this is going to be very tough to analyse.

SteveBaker (talk) 00:32, 25 April 2010 (UTC)

Salt fingers require Double diffusive convection. You have to consider both the diffusion of the heat and the diffusion of salt (or sugar in this case). These problems are not trivial even with knowing all the properties of all the components. I went to a course on DDC (and started the Wikipedia article on it) but it was too long ago. --BozMo talk 19:55, 26 April 2010 (UTC)

First human

This may sound oversimplified, but evolutionarily speaking, would the mother of the first homo sapien have been a different species than her offspring? Spellcast (talk) 20:49, 24 April 2010 (UTC)

Strictly speaking no. Because to breed, both parents would need to be of the same species in order to produces fertile offspring. Yet, I have this feeling that some one will post... Yeah But !... --Aspro (talk) 22:14, 24 April 2010 (UTC)

Here is the Yes But bit Neanderthal#Interbreeding_hypotheses. --Aspro (talk) 22:24, 24 April 2010 (UTC)

Yeah but "able to reproduce with fertile offspring" isn't really a satisfactory definition of species. See Species#Definitions_of_species for 14 different definitions of what constitutes a species, of which "fertile offspring" is just one. Most of these definitions would say that the mother was indeed the same species as her child, assuming that she was pretty much like her child in most respects. Which would make the child not the first homo sapien, leading to a paradox. Conclusion: there is no single definition of what exactly constitutes a species, and you have to be comfortable with some blurry boundaries between one species and another. Staecker (talk) 22:41, 24 April 2010 (UTC)

Species is a fuzzy, fluid concept, so there's really no point in trying to establish a final cut-off on who was human and who was just a dirty ape. Vranak (talk)

Interesting argument by Dawkins here Count Iblis (talk) 23:21, 24 April 2010 (UTC)

Ah yes, I'm glad you linked to that interesting article, which I now recall reading years ago. Dawkins' mention of ring species is quite useful in applying here. Spellcast (talk) 01:30, 25 April 2010 (UTC)

Yes, an excellent article by Dawkins. Thanks Count Iblis. It reinforces the notion that a new or different species is identified in retrospect rather than at its first appearance. When a number of creatures are determined to be different to other similar creatures we say they represent separate species of the same genus. It won't necessarily be unambiguous so there is likely to be learned debate about where the boundary lies between the two species. (Genetically, there are millions of differences within any one species.) There is also likely to be speculation about how many thousands of years ago the two species diverged. It certainly won't be possible for the mother of a new-born to say Whoops, I've given birth to the first member of a new species. Dolphin (t) 07:00, 25 April 2010 (UTC)

If we had a solid definition of what is a human - some kind of a bright-line measurement (or set of measurements) - then you could say that the mother of "the first human" was (by definition) not human. However, we don't have a measurement like that. When we look back through the hominid fossil record, we see slow, continuous, change from something that's clearly an ape-like non-human to something that clearly is human with perhaps a couple of million years between those two fossils. We cannot put a stake in the ground and say that at on April 12th on 2123456 BC there was a sudden change between the "obviously not human" and the "obviously human" in the fossil record.

Evolution isn't like that...well, mostly it's not like that. If we look at a specific attribute of what makes us what we are, there are abrupt changes. The one I usually trot out at times like this is the evolution of lactose-tolerance in adults. There is a very specific change on chromosome 2 that flips a switch between lactose tolerance and lactose intolerance - there is no halfway house here. You are either one or the other. So we know for sure that the first lactose-tolerant human child was born of a lactose-intolerant human mother (probably around 4,000 to 6,000 years ago in some part of the world where people started to farm sheep and goats on a large scale).

So if you found some single, special feature of humanity that was controlled by an "on/off" gene like that - then you'd be able to point to that specific baby that had that specific gene and say "definitely human" - and to the mother of that baby and say "definitely not human". But we don't have such a specific gene...if we did, we'd probably be able to point to a specific skull in a long line of them in a museum someplace - and say "that one is human - that one isn't" - but we can't do that, so there is no single gene that we've chosen to mean "human" or "non-human".

That's not to say that we couldn't do that - we could look at our nearest relatives (chimps, gorillas, etc) - find a gene that we have that the chimps and gorillas don't have - and label that "the human gene". But doing that would be extremely controversial. Suppose we picked a particular gene on the long arm of chromosome 7. A child born with a rare genetic condition called "Williams disease" might well be missing that gene. Are we then going to label that child "not-human"? Of course not! But if we picked a bright-line definition of "human" then this kind of thing would happen all the time. I don't think we have the cold-hearted scientific rigor to do something like that.

Our modern definition of "human" is something like "born of a human mother" (although "born from an egg produced by a human mother" might be a better choice if we were to develop artificial wombs or something in the future). But that definition leaves us with a very definite "chicken and egg" problem.

So we have to accept that "humanity" isn't a black-and-white thing. There have been animals around in the past that have been "almost human" and others that are "somewhat human" - but nowhere has there been a step where a "definitely not human" gave birth to a "definitely human" child. What happened was that a "49.9% human" mother gave birth to a "50.1% human" child, the child looked, behaved and performed more or less identically to his/her brothers and sisters - looked like his/her mommy - maybe was slightly better at the "walking upright" thing - maybe fractionally more intelligent - maybe a tad less hairy...but not so much that you'd notice.

In the end, like so many RD:Science questions, this is not about science - it's about the definition of a word. What the OP is asking is a matter of linguistics. I recommend reading Chicken or the egg - an odd article - but actually very meaningful in the context of this question.

SteveBaker (talk) 00:13, 25 April 2010 (UTC)

Since lactose tolerance in adulthood is determined by a single gene, as you say, it probably occurred multiple times spontaneously, which complicates it. --Tango (talk) 01:13, 26 April 2010 (UTC)

The current evidence is unclear but it's possible only one lactase persistence mutation persisted, see Lactose intolerance#History of genetic prevalence and also [10] [11] [12]. Nil Einne (talk) 14:26, 26 April 2010 (UTC)

I think Tango was (pedantically) commenting on Steve's statement that the first lactose tolerant person was born while people were farming goats for milk. Since it (ie lactose tolerance) is determined by a single gene, it quite likely randomly came up at a previous time when there wouldn't have been any selective pressure to support it. 41.213.125.249 (talk) 15:17, 26 April 2010 (UTC)

See http://www.onelook.com/?w=homo+sapiens&ls=a. - Wavelength (talk) 00:25, 25 April 2010 (UTC)

...and in what way does that help? All of those dictionaries say things like "The primate species of mammal to which modern humans belong. Homo sapiens is Latin for knowing man or wise man."...but that completely fails to draw a bright line between this species and other, older species. It also fails in that the word "species" is a totally fuzzy, inadequate term. There is nothing in any of these definitions that would allow you to say "This creature is a human...that one isn't"...and that's what it would take in order to provide a "Yes" answer to our OP's question. Without such a 'bright line' definition (which would undoubtedly have to be genetic in order to be useful) - the answer is a clear "No" - there is no small step along the way from ape to human at which you could say that the mother was non-human and the child was human. SteveBaker (talk) 06:59, 25 April 2010 (UTC)

While there have been good answers, no one has linked to Speciation which discusses the general concept. Nil Einne (talk) 16:29, 25 April 2010 (UTC)

The question is invalid, like the one about chicken and egg (you can find that article on Wikipedia, too). Also consider that the brown bear and the polar bear routinely mate in the wild, when they are obviously on diverging evolutionary paths. Imagine Reason (talk) 11:52, 26 April 2010 (UTC)

Indeed - and if you need an example that's from a pair of animals that have diverged a little further than that, consider the situation with horses and donkeys (which produce mules) and between lions and tigers (which produce tigons and ligars). In those cases, the divergence produces offspring that are generally infertile. (I believe the offspring of brown and polar bears are fully fertile). As divergence increases still further, producing live offspring from mating becomes impossible - and with yet more divergence, even mating becomes impossible. Like so many things in biology, there is a rather smooth/continuous variation between "same species" and "different species" and coming up with useful, firm definitions for words like "human" and "species" is impossible. SteveBaker (talk) 12:36, 26 April 2010 (UTC)

And you have the "humanzee", the mythical human-ape hybrid- In 2008 a Scottish scientist wanted to give it a try [13]. Ethical problems abound. From the last link "The Human Fertilisation and Embryo Bill prohibits the placement of animal sperm into a woman The reverse is not prohibited. It's not even mentioned.".

We don't an article on blynxes, a hybrid of bobcat and lynx: "In 2003, DNA analysis confirmed that five odd-looking felines found in Maine and Minnesota were bobcat-lynx hybrids, dubbed blynxes."[14] --Enric Naval (talk) 15:54, 26 April 2010 (UTC)

A better latter link would be to Canadian lynx (Lynx canadensis), since the bare 'linx' links (ha!) to the Genus, which of course includes the bobcat (Lynx rufus). 87.81.230.195 (talk) 20:15, 26 April 2010 (UTC)

April 25

relation between the expansion of orbits and of the universe

It seems quite reasonable that because orbits like the Moon can expand that such expansion could the explanation for the expansion of the Universe since orbits seem to be a Universal phenomenon, pun intended. Indulging this line of thought consider that somewhere then there must be a center about which everything orbits which probably contains the center of mass as well. What science denies that such a center exists and that orbit is only a local phenomenon and not one that is totally universal? Plain vanilla with chocolate chips (talk) 05:28, 25 April 2010 (UTC)

I'm sorry - but what you are suggesting makes zero sense.

Why would you think that the gradual expansion of the moon's orbit would have anything to do with the expansion of the universe? The gradual increase in the moons' orbit is caused by gradual consumption of the moons' kinetic energy as it raises tides - there is no such mechanism happening in the universe as a whole. You can't just say "Thing A is expanding because of reason B, hence the expansion of thing C must also be because of reason B."

So I'm not going to "indulge this line of thought" - because it's 100% wrong. There doesn't have to be a "center" about which everything orbits or a "center of mass" because this whole orbital theory of yours is not remotely true:

• We know the universe is expanding because we see redshift in light from distant galaxies.
• Einstein field equations of general relativity explain why this is happening in mathematically specific form.
• General relativity is an exceedingly well tried and tested theory.
• Furthermore, many experiments - including the decisive observations of the cosmic background radiation) prove conclusively that space has been expanding ever since the big bang.

To be credible, your "explanation" would have to explain why Einsteins' field equations are somehow incorrect and explain why we observe all of the other effects of general relativity and somehow find another explanation for all of those experiments which you are (in effect) saying must be false.

Science does not allow you to just come up with a mental model that (to you) explains something you don't understand. You also have to tie that in to all of the other aspects of physics that relate to that idea. You won't be able to do that - which is why we know you're wrong.

I suggest you carefully read Metric expansion of space which explains what we know - how we know it - and (crucially) which experiments have been done to show that these theories correctly explain our observations...but "orbits" have nothing whatever to do with that.

SteveBaker (talk) 06:48, 25 April 2010 (UTC)

Gravity is often depicted as an indentation on a grid. How do you express the moon's expanding orbit on this grid? Does the grid become flatter and flatter in the area of the moon's orbit and it so what happens if it becomes entirely flat? Same question for the Universe assuming there is a center around which everything else orbits? Would not this flatter and flatter grid represent the expansion of the Universe as the area of orbit furthest from the center just like we see in galaxies? Plain vanilla with chocolate chips (talk) 09:06, 25 April 2010 (UTC)

The indentation stays the same, since the mass of the Earth doesn't change. Imagine you have a big bowl and roll a marble in it - depending on how fast you roll the marble, it will go around the bowl at different heights (it will gradually move lower due to friction, but that's a limitation of the analogy - there is no significant friction for the moon). The tidal interaction between the Earth and Moon just changes the height of the orbit since it changes the speed of the moon. --Tango (talk) 13:49, 25 April 2010 (UTC)

The moon doesn't move outwards due to consumption of energy, really, (that doesn't make much sense - energy is conserved, so it is just transferred not consumed). It is due to the lag between the moon's current, always moving, position and the tidal bulges it causes (the bulges take time to move, so lag behind the moon). The gravitational interaction between the moon and those bulges results in a transfer of angular momentum between the Earth and moon. --Tango (talk) 13:49, 25 April 2010 (UTC)

Indeed, energy never "goes away" it's just converted to another form. However, we don't usually go around talking about how the batteries in our flashlights transferred all of their energy to this and that form - we say that it ran out of energy and those who care about those kinds of things understand what we're talking about. So, sure, the kinetic energy of the moon is converted into heat and into making the earth rotate a bit faster...both a consequence of tidal effects. But the bottom line is that the moon loses kinetic energy due to tidal effects and that's causing it's orbit to slowly get bigger. SteveBaker (talk) 18:11, 25 April 2010 (UTC)

I would be inclined to agree partially with the original post in that the earth revolves around the sun, the solar system aroung the galaxy and the galaxies around some greater point, what is that point?

There is no evidence that the galaxies are rotating around "some greater point". They rotate about their own centers - but precisely because there is no "center" to the universe - there is no larger scale rotation going on. That's yet another reason why this idea is a non-starter. It's tempting to think that because moons orbit planets and planets orbit stars and stars orbit galaxies, that there should be some higher order rotation - but there isn't...so right there (and in a dozen other ways) this theory falls to the ground. It is as I said before - you can't understand the universe by just thinking stuff up in your head - your hypotheses have to fit in with all the other bits of known science - and this hypothesis of yours doesn't do that...not even close! In your mind, this idea "fixes" something you evidently don't understand about the metric expansion of space - but it "un-fixes" a million other things we know with great certainty! SteveBaker (talk) 18:11, 25 April 2010 (UTC)

Some of the larger galaxies do have smaller satellite galaxies orbiting them. The OP might also be interested in the Local Group article, which describes what the Milky Way, and the Andromeda Galaxy etc are doing, the Virgo Cluster and Virgo Supercluster articles, which describes how they are bound to other groups, and the large-scale structure of the cosmos article which describes the situation in general. CS Miller (talk) 22:14, 25 April 2010 (UTC)

See the true expansion of gravity Plain vanilla with chocolate chips (talk) 09:50, 25 April 2010 (UTC)

We can measure the distance to the moon and theorise about what ought to happen to that distance. There is no significant discrepancy between the measurements and the predictions, so we don't need to try and come up with another explanation. --Tango (talk) 13:49, 25 April 2010 (UTC)

(To the question three paragraphs ago about orbits): What is your evidence that "the galaxies" are in orbit around some point? --ColinFine (talk) 14:04, 25 April 2010 (UTC)

I have not read Ismail Kaddah's article at Academia.Wikia. All I have seen is the diagram he uploaded which shows a theoretical (IMHO) center of the Universe around which things that orbit each other orbit so you will have to ask him. Plain vanilla with chocolate chips (talk) 15:58, 25 April 2010 (UTC)

Academia.Wikia is not a peer reviewed journal (their "peer review" process doesn't seem to include any verification of credentials, so cannot be consider to be peer review), so you shouldn't trust any theories posted there. If the theory was likely to have any validity, it would have been published in a real journal. --Tango (talk) 17:54, 25 April 2010 (UTC)

That wikia piece is complete incoherent gibberish. You should ignore it. Wikia is a terrible place to go to find truth and fact. Wikia's policies allow anyone to write anything. I could write an article saying that electricity is carried around by tiny little green men in recycled WalMart shopping bags - and it would be accepted there. Without any kind of control of reliability (such as we have here on Wikipedia) - you simply cannot trust anything that's written there. It truly is a waste of disk space. SteveBaker (talk) 18:11, 25 April 2010 (UTC)

If an object is orbiting below the synchronous rotation orbit height, then it will slow down, and reduce its orbit height until it either enters the atmosphere or collides with the surface, see tidal acceleration. CS Miller (talk) 22:25, 25 April 2010 (UTC)

Someone mentioned that part of the energy drained from the moon is transfered to earth's rotation, speeding it up. That's not correct. The earth is actually slowing down its rotation. Dauto (talk) 15:34, 26 April 2010 (UTC)

Physics-Question regarding Vacuum

What happens when a fan is switched on inside a perfect vacuum? Imagine a glass room that is completely sealed. Perfect vacuum is maintained. A battery is kept in and a fan be connected to it. If we switch it on with any remote controller, will it run or what happens? —Preceding unsigned comment added by Srvnbv (talk • contribs) 06:17, 25 April 2010 (UTC)

It is very easy to answer this question without having to achieve a vacuum. Simply remove the fan blades and run the electric motor. Without a load on the motor it runs at its zero-load speed. Contrary to what you might imagine, the unloaded electric motor doesn't keep accelerating forever. Electric motors have an equilibrium speed determined by their power source and their system of magnetic field and wiring. With no load, the motor will run at its no-load speed. When the motor is loaded, such as with a fan, it runs at a speed somewhat slower than its zero-load speed. Have a look at Synchronous motor. Dolphin (t) 06:25, 25 April 2010 (UTC)

Also, I suspect that the motor may overheat, since it lacks moving air to cool it. Radiation cooling is still possible, as is conduction cooling to the case, but probably wouldn't be sufficient to cool a motor designed to use forced air cooling. StuRat (talk) 07:02, 25 April 2010 (UTC)

If the motor has internal friction (as all "real" motors do) - then the fan would run quite a bit faster than it would in air - but the system would quickly reach an equilibrium at which point all of the electrical energy coming from the battery would go into overcoming friction. If you imagine a totally frictionless motor - then it would either continue to speed up faster and faster so long as you kept a charged battery connected to it...or it would cease to draw power from the battery when it reached a certain maximum speed. (Which of these things would happen depends on the design of the motor). SteveBaker (talk) 07:07, 25 April 2010 (UTC)

There is a limit on how fast the magnetic polarity of the motor's electromagnets can be swapped, which must occur at least twice per revolution (and for most motors, a lot more). This in turn limits the speed of the motor. CS Miller (talk) 09:14, 25 April 2010 (UTC)

If we're talking about the portable battery operated fans that we use in our motor-homes, hobby shacks, etc. then it would be a cheap-an'-cheerful brushed DC motor . It would speed up a bit with no load but the back Electromotive force being generated would limit its maximum speed . As the article Brushed DC electric motor explains As As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current through the motor drops as the rotational speed increases, and a free-spinning motor has very little current. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases. So it would run a bit cooler without load, but without some gas present to aid cooling, it would get hotter and hotter. The cheap-an'-cheerful bearings are unlikely to be lubricated with vacuum grease (nor employ dry running ceramic ball bearings) so there goes your hope of maintaining a perfect vacuum. The insulating vanish on the windings would start out-gassing with the rising heat too. The plastics would also 'out-gas' and you'd lose perfect vacuum that way too. You would lose vacuum faster than you could pump out the vapours and thus the motor would then start to lose heat. A quick consideration of the tribological effects of the vacuum and one has to ask what happens as the lubrication evaporates and the bearings dry. Without their lubrication (and protective oxide layers) the metal will (or may, depending on different things) start to form many temporary 'micro-welds' creating heat and the micro-weld particles and rough surfaces produced from this, increasing the friction. The carbon brushes will also wear out and fail in a very much sorter time when run in a vacuum. Another phenomena you might witness as the commutator spins: that without the presence of air to quench all those little sparks, a low voltage Corona discharge may lead to speed loss due to shorting. Putting all that together: The fanless fan, would most likely seize first, and if there is no current trip, the windings will (in places) short and glow about 'cherry red' (at which point it will be radiating heat more efficiently), until the conductors sublimate into space/vacuum and an open circuit condition is achieved. If NASA could ignore these problems, it could buy most of its stuff from RadioShack and space exploration would be a lot cheaper. --Aspro (talk) 09:38, 25 April 2010 (UTC)

And why (not) on Earth would NASA want to create a fan capable of functioning in a vacuum ? StuRat (talk) 14:55, 25 April 2010 (UTC)

Say an evil extra terrestrial alien bent on World domination turns up. Do you think we could win with our puny weapons? But it wouldn't matter if this evil little **** hits the fan first :-) --Aspro (talk) 19:37, 25 April 2010 (UTC)

:-) StuRat (talk) 20:50, 25 April 2010 (UTC)

power in watts used when sending a phone text message.

any estimates for this ...sending a text phone message , a tweet, a facbook update? I know the phone powers up as you can hear interference on electrical equipment. —Preceding unsigned comment added by 89.241.1.51 (talk) 11:45, 25 April 2010

According to Mobile phone radiation and health, a GSM phone emits a peak power of 2W, other technologies rather less. The actual power radiated will not depend on the content, but on how accessible the base station is. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

The watts used depends on how far the base station is. But a text message transmits for a very short time - just a chirp, rather than the continuous transmission with voice. Your phone makes these "chirps" anyway, even without a text message, all the time, so that the base station can keep track of it. Ariel. (talk) 08:14, 26 April 2010 (UTC)

What is suprastine

I'm assuming that this was intended to be a separate question, and have made it into a heading. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

I don't know. Wikipedia and Google both say "Do you mean suprastin?". In WP that redirects to Chloropyramine. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

I would agree. Suprastine is a misspelling of suprastin. Ariel. (talk) 08:16, 26 April 2010 (UTC)

Riding a bicycle - reducing energy used per mile

Air resitance increases with the square of speed, but what about rolling resistance? I recall hearing that it decreases with speed, is that correct? My own experience of going on long rides using a conventional bike is that it feels like you are using less energy per mile the faster you go. Is that impression correct please? Is there an ideal speed that balances wind resistance and rolling resitance?

I have always cycled in old jeans and so on. Would I notice any difference in air resistance if I wore the lycra fetish clothes that racing cyclists wear? I probably only cycle at about 10 miles per hour, although I may get fit enough and practiced enough to go faster.

I like going for long rides of say 40 miles through the english countryside. I am not particularly interested in speed, but am very interested in what is best regarding doing long rides without getting very tired on the way home. Thanks 89.243.216.99 (talk) 13:36, 25 April 2010 (UTC)

Hi 89.243, I can't answer your question off the top of my head, but Bicycling Science by D G Wilson is excellent. I think the gist of it is that the most cost-effective way of reducing rolling resistance is making sure your tires are pumped up (and not using knobbly MTB tyres if you're on the road). Bicycling Science also has extensive chapters on energy consumption and air resistance which will be of use to you. Some informed speculation for you: unless you're wearing MC Hammer-style trousers, I don't think switching to lycra will save you much energy: Richard's Bicycle Book (in one of its incarnations at least) says that shaving ones legs will only take about 0.125 seconds off someone's time for a 40km time trial, or there abouts. I would be surprised if the advantage is much more pronounced between jeans and tights. Most people I know find that shorts surpass jeans when it comes to comfort over distance, as there's less to flap about, it's cooler, there's less chafing, your knees are more free to move and if you get wet you don't get stuck in cardboard-like soggy denim! Happy cycling. Brammers (talk) 15:55, 25 April 2010 (UTC)

Thanks, I read parts of the book, but could not see anything about rolling resistance and speed unfortunately. 89.243.216.99 (talk) 17:50, 25 April 2010 (UTC)

Had a rummage for you (would have done it sooner but I left my copy at home and I'm at uni now). This chart shows that although rolling resistance is velocity-dependent, the difference in rolling resistance at two (fairly extreme) speeds decreases sharply with tyre pressure. The data is for car tyres, but I think that since bicycle tyres are pumped to about 5 bar (70 psi) and travel at much slower speeds, the change in rolling resistance with speed would be negligible. Brammers (talk) 10:33, 26 April 2010 (UTC)

One correction - the horsepower required to overcome air resistance increases as the CUBE of the speed - not the square. The power to overcome rolling resistance increases roughly linearly with speed. So from a pure mechanical energy consumption perspective, slow is without doubt better. However, this is a human-powered system - and humans are not simple machines. It takes a certain amount of energy to pump your legs, breathe, maintain body temperature and all sorts of other things that may be completely independent of speed. In that case, getting there quickly has benefit to you - even if you have to apply more power to the bicycle to do it. The trouble is that doing analysis with a human in the loop takes this out of the realm of simple mechanics and into complicated biochemistry stuff...which is the point where I have to shrug and say "I dunno". SteveBaker (talk) 17:46, 25 April 2010 (UTC)

Agreed. But the secret to avoid getting "very tired" on the way home is to eat some carbs while on the bike (or on a break - I'd rather have a nice plate of pasta than the chemical paste used by racers). Once you've run down your glucose levels, the body goes into energy saving mode, and every km hurts. I once rode down from Trento to Lake Garda with a nice backwind, and found out to late that all shops and restaurants were closed. The way back was somewhat less than pleasant... --Stephan Schulz (talk) 20:24, 25 April 2010 (UTC)

Power increases with the cube of speed, but the OP isn't talking about power (which is energy per unit time), but rather energy per unit distance. That cancels one of the speed factors, so turns the cube to a square. Alternative proof: Air resistance, as a force, is proportional to the square of speed (this is well known). Energy=Force x distance (for constant force, which we have), so energy per unit distance is just force. --Tango (talk) 21:20, 25 April 2010 (UTC)

Above ten miles an hour, you're always going to use more energy the faster you go. The most important factor for rolling resistance is your tires -- you want the thinnest, smoothest tires with the highest air pressure. The problem with pushing that to the limit, though, is that with "racing" tires you get a heck of a lot of flats (and keeping them inflated is a bore). The next most important factor is to have good bearings that are well lubricated. The next most important factor, I think, is the frame, and particularly the fork -- a carbon fork is very springy and doesn't absorb much energy from the roughness of the road. Looie496 (talk) 21:56, 25 April 2010 (UTC)

The most important factor is actually getting a well-fitting bike. Bikes are quite efficient machines, so you are bound to lose more energy due to bad ergonomics than due to rolling resistance. And, surprisingly, all other things being equal, a fatter tire has a lower rolling resistance than a slimmer one. Slimmer ones are lighter, have less air resistance, and are faster to accelerate, but at the same pressure, they actually have higher rolling resistance. --Stephan Schulz (talk) 22:20, 25 April 2010 (UTC)

Recumbent bikes have far less air resistance than normal ones, especially the fully enclosed ones. Thus they need less energy to move, or your top speed is far higher. CS Miller (talk) 23:27, 25 April 2010 (UTC)

Would changing from knobbly tires to smooth ones make much difference in the energy required to travel a particular distance please? 78.151.144.28 (talk) 11:30, 26 April 2010 (UTC)

Yes, it makes a noticeable difference, but the pressure in the tires makes even more of a difference (in my experience). Looie496 (talk) 17:21, 26 April 2010 (UTC)

What to do with left over cooking oil?

Is the any way to convert this into electricity (quietly) in a domestic situation? I have a small brick garden shed and a first floor flat with an attic, and it is possible to send a 240 volt cable from shed to my flat. Also, is there any way to power my 36 volt electric bike by the same method? [Trevor Loughlin]80.1.88.25 (talk) 14:28, 25 April 2010 (UTC)

There is a way to use used cooking oil to power an internal combustion generator, basically all you need to do is filter the oil and maybe make a few adjustments to the engine. So, you could power a generator. You would get an odor, but it actually smells good, like fried food. The noise is another problem, as neighbors wouldn't want to hear that at night. You could charge the batteries on the electric bike using such a generator, too. However, you would need large quantities of used cooking oil to make this all worthwhile, which usually means you need to have restaurant(s) willing to donate their oil to the cause. StuRat (talk) 14:48, 25 April 2010 (UTC)

(EC) You can find plenty of homebrew guides for making biodiesel from used/waste vegetable oil online. [15] [16] [17] www.ehow.com/how_5254968_make-biodiesel-out-waste-oil.html www.squidoo.com/Making-Biodiesel-At-Home-Using-Waste-Vegetable-Oil. I presume many diesel generators should work with this either directly or blended with regular diesel. (Generally people do it for cars where the conversions to run on waste vegetable oil are expensive, and damage and problems due to the oil difficult and costly to repair, and the tolerances and conditions required more difficult.) It's a lot of effort if all you have is a small amount of oil from home use however.

A quick search also finds plenty of references to generators that can use the oil directly. E.g. [18] [19] [20] [21].

However most of these look big so I'm guessing cost quite a bit and I somewhat doubt they'll be cost effective unless you want such a big generator for other purposes (e.g. if your house is completely off the grid) particularly if your only supply is from your home, unless you run some sort of home-business where you deep fry stuff and have large amounts of oil. This one for example is targeted to restaurants [22]. (Actually even a say $250 generator is not going to be cost effective but it's less extreme then buying a $5000 generator to use it for 30 seconds.) And getting another supply may not be easy, many restaurants are already selling their waste oil I believe (see Vegetable oil#Waste oil).

You can of course try making or converting a generator yourself [23] [24] but I'm guessing this may be beyond your capabilities.

BTW Vegetable oil fuel may be of interest.

Incidentally, I wouldn't recommend running a mains wire by yourself, especially one that is exposed to the elements.

Nil Einne (talk) 15:15, 25 April 2010 (UTC)

What you need is a diesel generator - these cost between $800 and $1500 (new). You can filter the oil and take measures to remove the water - and use that to power the generator - which in turn can drive electrical appliances - or power the battery charger for your bike. You do need quite a lot of oil to make this worth-while though. If you have just a couple of pints a week - or even a couple of pints per day - then the cost hand hassle of the generator would probably not be worth it. You'll need a diesel generator though - doing this with a regular gasoline powered generator would require converting the oil into gasoline and that requires a lot of complicated chemistry. See: Vegetable oil fuel and Biodiesel SteveBaker (talk) 15:58, 25 April 2010 (UTC)

It's easy to spend more money than your going to get back. The article on Domestic_energy_consumption show more energy is consumed (whether as gas, electric, oil etc.) for heating than for lighting. A Micro combined heat and power unit might be more economical if you are able to do the plumbing yourself. They can use gas (of most types) too, if you run short on oil. You might find Microgeneration a useful article to read for more inspiration. Also, make sure you have your roof fully insulated (there are all sorts of grants available for some of these things) and ask your down-stairs neighbour to turn his heating up in the winter, which will help save on your heating costs.--Aspro (talk) 16:31, 25 April 2010 (UTC)

You could perhaps try a model steam engine with a dynamo or a thermo-electric generator. Burning the oil direct like a candle has a fire risk and may be unhealthy like secondary smoking. 89.243.216.99 (talk) 18:33, 25 April 2010 (UTC)

If you heat with heating oil you might be able to just dump the stuff in your tank. And what do you know, we have an article on that: Bioheat. Ariel. (talk) 08:08, 26 April 2010 (UTC)

Oil won't burn as readily, so it wouldn't be feasible to use it to run an engine, which needs a quick-burning fuel like gasoline to provide the sudden thrust of power.--Cheminterest (talk) 22:24, 26 April 2010 (UTC)

What if I built my own multi-cylinder Stirling Engine to run a generator, with a series of candle-like wicks to heat the bottom of the cylinder, but with the cooking oil instead of wax as the fuel? As for the amount of oil, my own fry-ups already amount to a gallon this month.

homoaromaticity in dimedone?

I'm trying to figure out why dimedone is almost as acidic as barbituric acid, compared to other diketones (3 pKa drop). One thing I've been thinking about is homoaromaticity (and the aromaticity-stabilisation for barbituric acid probably is significantly reduced because of the number of heteroatoms and EWGs involved). John Riemann Soong (talk) 17:23, 25 April 2010 (UTC)

Oh the same inquiry especially goes to Meldrum's acid, which would appear to have 6pi electrons. John Riemann Soong (talk) 17:28, 25 April 2010 (UTC)

This is continuation/follwup of Wikipedia:Reference desk/Archives/Science/2009 November 23#acidity of dimedone, barbituric acid and acetylacetone. DMacks (talk) 17:54, 25 April 2010 (UTC)

Anyone? This is a REALLY curious phenomenon. Why is it so ill-studied? John Riemann Soong (talk) 03:01, 26 April 2010 (UTC)

If you draw your ideas out in ChemDraw, I'll happily have a think about them. At the moment it's a bit difficult to see what you're seeing.

Ben (talk) 11:43, 27 April 2010 (UTC)

Volcanoes

How do volcanoes make lightning? In the news a few days ago, they showed a picture of that volcano in Iceland with lighting coming out of the ash cloud. Also, the cover of my physics textbook has a picture of Sakurajima with a bunch of lightning coming out of it. --75.34.67.8 (talk) 17:49, 25 April 2010 (UTC)

Somewhat off the top of my head, I believe it is just static electricity generated through friction, similar to 'normal' lighning, though it appears the exact mechanism, as for lightning, is not understood completely. See Dirty thunderstorm, also a mention in the WIkipedia Lightning article. This site might help thunderbolts.info though it seems rather "fringe science" on a quick look (looks like your Sakurajima piccy too). This National Geographic article, Volcanic Lightning Sparked by "Dirty Thunderstorms" and this one New Lightning Type Found Over Volcano? seem more reliable. And this IEEE—Volcanic Lightning article. Try this pic from Chile Chaitin volcano, May 3 2008 Awesome! There is actually a lot on the net, try Googling "volcano lightning cause" for more info.--220.101.28.25 (talk) 19:00, 25 April 2010 (UTC)

Here is a site that has some good technical attempts to explain the phemomena. geology.com --220.101.28.25 (talk) 19:32, 25 April 2010 (UTC)

Is this correct?

An atom is moving in the +x direction and a laser beam is headed in the -x direction. The atom absorbs a photon and emits it in the -x direction. What is the photon's energy?

Answer: I think that in the atom's reference frame, the photon's energy is hf*sqrt(1+v/c)/sqrt(1-v/c) before absorption. After emission, the photon's energy is still hf*sqrt(1+v/c)/sqrt(1-v/c) in the atom's reference frame. However, blueshifting this into the lab's frame gives hf*(1+v/c)(1-v/c) = hf*(1+2v/c). Is this correct? --99.237.234.104 (talk) 18:01, 25 April 2010 (UTC)

This is a very tricky question, but I think the energy does not change. Are we assuming the photon is emitted with the same frequency that was absorbed (relative to the atom)? The light is blueshifted relative to the atom when absorbed. The photon is then redshifted relative to the atom when emitted and ends up back where it started. The atom basically did nothing - it picked up the photon, and then let it go. Perhaps the assumption is that any energy absorbed is then emitted? That gives the same result. Are you wondering if the atom can give the photon energy in some way? From the atoms point of view, it's not moving, and has no energy to give the photon. The only way the system as a whole can transfer energy from the atom to the photon, would be to slow down the atom, and speed up (well, "mass up") the photon, but conservation of momentum does not allow that, because a heavier photon would give the atom a larger kick - but then the atom is actually moving faster, not slower. Ariel. (talk) 07:48, 26 April 2010 (UTC)

(OP here) What do you mean by "the photon is then redshifted relative to the atom when emitted"? Assuming that the atom's momentum is much larger than the photon's, the photon should have the same frequency relative to the atom as it did before absorption: in other words, hf*sqrt(1+v/c)/sqrt(1-v/c). However, in the lab frame, moving at speed v relative to the atom, the emitted photon should appear blueshifted: E=hf*sqrt(1+v/c)/sqrt(1-v/c) * sqrt(1+v/c)/(sqrt(1-v/c). This is approximately hf(1+2v/c). I think this should be the answer, but I have an answer key that contradicts this, saying that E=hf if only terms first-order in v are considered. --206.130.23.2 (talk) 16:25, 26 April 2010 (UTC)

You are right, I meant observer not atom. Let me start over. The observer is located at -x. He sees the photon emitted, with no shift. The atom sees the photon with a blueshift, and absorbs it. The atom then emits the same (higher) frequency it absorbed. To the atom this emitted photon in not shifted, but it is at a higher frequency that it started. To the observer the emitted photon is redshifted, because the emitter (the atom) is moving away from the observer. The end result is no change. Ariel. (talk) 20:47, 26 April 2010 (UTC)

If you make your frame of reference the atom, then the atom absorbs and emits the same, unchanged (from it's point of view) frequency. How do you know the atom did not change speed? Because it absorbed momentum by catching the photon, it then lost exactly the same momentum be emitting it. So it could not have changed in speed. No (net) change in speed for the atom means the photon's energy could not have changed. Ariel. (talk) 21:14, 26 April 2010 (UTC)

If you choose the +x observer instead, then you might think that when the photon is emitted from the atom it's blueshifted - since it's heading toward you. But actually, think about it in a different way. The photon is emitted with full speed, but the motion of the atom is away from the direction of the photon, meaning that the photon now is slower (since the motion of the atom robbed it of some speed). Photons are not actually slower, instead it red shifts. This also is correct if the observer is at -x. It's actually correct for all observers. Because the motion of the photon, and atom are opposites, it makes no difference where the observer sits. Ariel. (talk) 21:14, 26 April 2010 (UTC)

That makes perfect sense. I don't know what I was thinking; I was just having another mental block. Thanks. --99.237.234.104 (talk) 21:53, 26 April 2010 (UTC)

Small windmill for electricity

I saw what looked like a home-made windmill recently, about a meter in diameter. It had blades all the way around, like the old fashioned things used on farms for pumping water, so it was not just a propeller. It was turning what may have been a bicycle dynamo. Has anyone any idea how much average power it would provide under average conditions? Thanks 89.243.216.99 (talk) 18:01, 25 April 2010 (UTC)

I don't think a one meter windmill is going to do you much good. A carefully constructed (but homemade) three meter windmill on at least a 20 meter pole (to get it above roof and tree height) will produce about 1kW.hr per day in the right location. Most homes consume 10 to 20 kW.hr per day...so don't get too excited about living off the grid! You can basically use the thing to drive a car alternator and thereby charge a bank of car batteries - and then use an inverter to turn that into mains A/C voltage so you can run things from it. If you have the tools and the DIY expertise, you could probably knock one up for a couple of hundred bucks. People who spent a lot of money (like maybe $15,000) on small, commercially made, windmills have had very mixed results. Some find that they perform no better than the home-built contraptions, on occasion not producing enough energy to run their own electronic control modules! Others seem to be getting maybe 50% of their household power from them. But that's not gonna be remotely cost-effective. If your electricity bill is (let's say) $200 a month - and the windmill is saving half of that - then it's going to take 150 months to pay for itself (well, actually more than that because you could have invested that $15,000 and made interest from it). Will the windmill actually last the 15 to 20 years it takes to pay for itself? I very much doubt it. The trouble with wind power is that it's horribly bad at small-scale installations. If you could get a few hundred neighbors to invest in a one megawatt windmill that you'd all share, then probably it would be worthwhile - but at the scale you can manage by yourself, I don't think windmills are the answer. Solar panels offer much more opportunity for cost-effectiveness - but only if you live somewhere with year-round sunshine. From every angle I've investigated, by far the most cost-effective thing you can do is to conserve energy with better home insulation, energy-efficient appliances and that kind of thing. SteveBaker (talk) 19:26, 25 April 2010 (UTC)

Depends. In the UK the grid companies are now obliged to buy the power back from you at three times the grid price, even if you use the power yourself (ie they have to sell what you use back to you for a lot less than they just paid you for it). They pay about 30p a unit whereas cheap rate night power in the UK is about 5p a unit and peak rate about 10p a unit. Reasonably site gives about 8 years payback on that basis. The societical sense is a bit more arguable but the political argument is that this is the only way to get enough units built to get the cost down. --BozMo talk 19:46, 25 April 2010 (UTC)

That seems ripe for someone to find a cheap way to draw and store as much 5p power as possible and sell it all back for 30p. Dragons flight (talk) 22:14, 25 April 2010 (UTC)

Hmmm... now how does one go about building a pumped storage hydroelectric generator, I'm sure no-one will notice if I flood the abandoned quarry at the top of the hill. I'm going to be rich! 131.111.185.69 (talk) 22:33, 25 April 2010 (UTC)

30p a unit? I wonder if that makes buying a "proper" windmill a good investment.

I have always been intrigued with the idea of having a twelve volt wiring system in a house in addition to the 220v (or 110v) one, and using the fittings designed for caravans, such as 12v lighting, 12v fridges, and 12v TVs. Then you might be able to avoid using mains electricity completely. Since its only 12v, it should be safe for competant non-electricians to do the wiring. Even very inefficient home-made windmills that cost very little could be worth having, and you could have several. Energy-saving lightbulbs only use a few watts, so perhaps they could be run although there would be the problem of stepping up the voltage.

Sometimes old houses have wells in the garden, so I wonder how much money would be saved by going completely off-grid in the Uk or elsewhere? 78.151.144.28 (talk) 09:39, 26 April 2010 (UTC)

You would need some seriously fat wires to run things at 12 volts. You would not save any money at all going off grid - you would spend much more. If people could save money going off grid everyone would be doing it already. Also, if you wire an entire house with 12 volts, you would have a ton of amps going through those wires - any mistake in the wiring and you would have a fire. So, going 12 volts will not let a non-electrician do the wiring. You might not electrocute yourself, but that's not the only hazard available with electricity. Ariel. (talk) 09:54, 26 April 2010 (UTC)

I'm doubtful you would get a "ton of amps" off a 12v car-battery set up. 78.151.144.28 (talk) 10:09, 26 April 2010 (UTC)

Car batteries (lead-acid batteries) have a very low internal resistance and they can pump out hundreds of amps in the case of shorts (which is useful for starter motors, but not for house wiring). --antilived^{T | C | G} 11:24, 26 April 2010 (UTC)

People have been electrocuted and died with as little as 3 volts - and you can easily take a 1,000,000 volt shock from an electrostatic discharge with no ill effects. It's not the voltage that kills you! You can most certainly be killed with the current from a car battery - and you can also start fires that way. SteveBaker (talk) 12:22, 26 April 2010 (UTC)

Best solution for home generation if you are already on or are close to the grid is an inverter so you can use ordinary AC appliances. But you could have one DC socket straight from it, for example to charge an electric car or perhaps to heat water for storage. Itsmejudith (talk) 17:09, 26 April 2010 (UTC)

Mass wrapping around a rod

Mass m is attached to a post of Radius R by a string. Initially it is at a distance r from the center of the post and is moving tangentially with speed v₀, and as the mass moves the string wraps around the rod. What is the final speed of the mass?

That angular momentum is not conserved I understand. But according to: http://physics141.uchicago.edu/2002/hw6.pdf (middle of second page) the total energy is conserved. I don't see why the tension wouldn't do any work. —Preceding unsigned comment added by 173.179.59.66 (talk) 18:05, 25 April 2010 (UTC)

It depends whether how much you your professor wants to simplify, and assume that the string is perfect/ideal/does not stretch or deform. In that case, the string length is exactly constant, and the only change in radius is due to the string wrapping around the pole. If you want to add complexity, you can add two parameters to the string: elastic stretching, which you can model with Hooke's law; and inelastic deformation, which you should model based on an empirical estimate. In any case, angular momentum is always conserved; it is just that you are only considering the rod/string in this problem; those do not constitute a closed system. The angular momentum is transferred outside of that system, to the person holding the rod (or to the Earth, if the rod is planted in the ground); and can be ignored for your considerations.

To estimate a spring constant for the elastic stretching of the string, I would suggest treating the string as an extremely stiff spring (say, thousands of newtons per meter for the spring constant). Of course, this value depends on the type of fiber the string is made of. For the inelastic deformation, we are modeling how much the string permanently degrades (fibres unwinding and changing microscopic position and shape). This is very hard to model, but easy to estimate from measurements. Work is done on the string to deform those fibres; some energy goes into heat, and some goes into the process of changing the material properties of the fibre. How much energy is used will depend on the fibre properties.

You can use the elastic model to simulate dynamics - but you should use a Lagrangian mechanics formulation, because you have multiple variables in an arbitrary coordinate-system (radius, height above ground, and string stretching displacement); each coordinate is described with its own set of kinetic and potential energy terms. Adding the inelastic term will be sort of like adding a "frictional loss" term; it may be best to simply approximate that with an "engineering fudge factor" numerical constant, so that you can match the modeled velocity and wind-up time to experimentally observed times. This is the "work" that is being done by the tension (really, only the inelastic deformation constitutes "work" / energy loss - the elastic stretching will cause a dynamic oscillation, but the net work done by that component is zero). (Well, if you want to be very complicated, you can use a more sophisticated spring law than Hooke's Law; then you could model separate dynamic losses for the oscillation that are distinct from the inelastic deformation; but this adds parameters that you need to experimentally measure, and it is not clear that the oscillatory loss would be caused by a different physical effect than the inelastic deformation anyway - so modeling it separately is dubious).

In any case, you can see that the added complexity may require messier math, more parameters, and (possibly) require a formulation of physics, Lagrangian mechanics, that has not been introduced to you yet (though you could try to do this with strict Newtonian mechanics, the algebra and the integrals will be very ugly and hard). Furthermore, it is reasonable to assume that the string stretching is "small" for most real problems (aside from rubber bungees). So, it may be easier to simplify than to include this added terms. Nimur (talk) 18:37, 25 April 2010 (UTC)

I'm assuming the string is ideal (and based on your answer, I'm glad I am). It's just that...as the mass starts falling in, isn't the tension applying a force which isn't perpendicular to the velocity. If it's pulling in the mass, it seems to me that it must... 173.179.59.66 (talk) 20:52, 25 April 2010 (UTC)

Actually I see it now, thanks. But what force applies the torque??? Is it the contact force between the rope and the string? Because then R and F would be parallel, and so I would expect no torque.173.179.59.66 (talk) 20:59, 25 April 2010 (UTC)

Note that the string pulls on the mass at any given time in the direction of the edge of the pole where the string touches the pole. As the string is winding itself around the pole, that point is changing, but what is important to realize is that the direction of the force is always some point on the edge of the pole and not the center of the pole.

So, you see that the torque relative to the instanteneous contact point of the string on the pole is always zero, but then the torque relative to the center of the pole is not zero. Count Iblis (talk) 21:54, 25 April 2010 (UTC)

Any chance of getting a reactionless drive out of this method?[Trevor Loughlin]80.1.88.1 (talk) 10:59, 27 April 2010 (UTC)

Detonations and the like

I should really know this but if I filled a small plastic fizzy drinks bottle with a liquid and the liquid blew off both ends (classic flower petal each way) does that definitely mean the liquid detonated? I was trying to blow the bottle up (essentially with compressed gas) but I was a bit surprised to see both ends go because I did not think the mixture was detonable. Presumably the drinks bottle are designed with a failure mode and I daresay it got hot but I cannot see why unless the pressure rose significantly on a timescale similar to the acoustic time between the ends one end shouldn't inevitably go first... what am I missing? --BozMo talk 19:41, 25 April 2010 (UTC)

If you slowly raise the pressure, you are likely to get a single point of failure, that's true, but it is still possible to get multiple, simultaneous points of failure, as you also get in an explosion. StuRat (talk) 19:47, 25 April 2010 (UTC)

Hmm. You said the bottle was full of liquid, but then you said you were trying to blow it up essentially with compressed gas. Please clarify. Looie496 (talk) 21:40, 25 April 2010 (UTC)

What did you fill it with? --Dr Dima (talk) 22:39, 25 April 2010 (UTC)

When we work with explosives, we use terminology very carefully (just like everything else). Usually we use detonation to describe the type of exothermic chemical reaction which produces supersonic gas - a shock front or shock wave. It is compared to deflagration, the type of exothermic chemical reaction that produces subsonic gas products. In your case you are not actually creating a chemical reaction at all - you are simply using a pressurized gas to expand explosively - so what you really have is a BLEVE - neither detonation nor deflagration - just rapidly expanding liquid and exploding vapor. Because you are using fizzy soda pop, your BLEVE gas is carbon dioxide, which is actually not ever in liquid state (only dissolved in water) - so the quantity of energy you release is small by comparison (the CO2 never boiled from liquid state, it just came out of solution). Also, carbon dioxide does not burn (in fact, it is a common fire extinguisher ingredient). So, your BLEVE is actually just a "EVE" - expanding vapor explosion. Do not try to create a BLEVE with other gases - some will rapidly combust on contact with atmospheric oxygen if the pressure and shock front conditions are right, and can not be easily extinguished. Nimur (talk) 00:23, 26 April 2010 (UTC)

(nighttime in the UK intervened) I was using the words carefully I thought and was asking about detonation. The mixture I was using was finely powdered mixed citric acid and KMnO4 with a dribble of water. I got banned from Chemistry as a school child for this mixture because of its delightful property of doing nothing for nearly a minute before eruptively evolving CO2 furiously and smothering everything with boiling MnO2 which is very destructive to teacher's clothing, skin etc (sigh, happy memories). But in general it just got hot and evolved gas. With the right proportions (no clues) sealed in a pop bottle it turns out it blows both ends of simultaneously. I am surprised if it is detonable but perhaps with the heat and pressure of the bottle it can be? --BozMo talk 06:25, 26 April 2010 (UTC)

FWIW though I think StuRat is probably right it was probably a coincident failure of the ends. --BozMo talk 10:42, 26 April 2010 (UTC)

I'm no expert, but I am pretty sure that permanganate-acid reactions do not create a shock-front (it is a very slow reaction as you are already aware). All you have done is over-pressure your container, which is not a detonation, properly. High explosive detonates even if uncontained; that is what makes them "high" (dangerous) and subject to legal and logistics controls. If you performed the same reaction without a soda-pop bottle, your reaction would fizz a bunch, but there would be no "exploding." Nimur (talk) 16:14, 26 April 2010 (UTC)

Again, just for the sake of droning, do not play with dangerous chemicals unless you know what you are doing. I mean, we're just random people on the internet and we can't stop you from doing whatever you are doing - but if you were thrown out of chemistry class, it's probably because you did something unsafe. Energetic materials can be a lot of fun, but you need to follow proper, cautious procedures - and the only way to do so is to learn from experts. At the high-school level, those experts are your chemistry and physics teachers. If you satisfy all of their (not so difficult) intellectual and safety criteria, you can move on up to playing with more interesting things - but it doesn't matter what kind of rocket scientist, construction engineer, or military demolition expert you are - people who work with energetic materials do not tolerate recklessness. (This includes splashing even harmless chemicals on lab benches. It sets a bad precedent). Nimur (talk) 16:25, 26 April 2010 (UTC)

In so far as this is directed at me, this is a reasonable remark but a little out of context. A couple of decades ago I spent a few years in industrial research blowing up some fairly major bits of kit (three people working for me had "fit persons" licences for high explosives and we had fun). I am now more interested in bucket chemistry to do with my own kids which is why I would rather avoid possible detonations. Mn2O7 of course detonates and permangate with strong acid is therefore worth avoiding. But as you I am reasonably sure that unlike nitrates etc it is otherwise relatively ok. I made fireworks as a kid myself and am kind of looking for something safer. --BozMo talk 16:37, 26 April 2010 (UTC)

It seems at least theoretically feasible to get an explosion (if not detonation) that way. If the reaction is slow enough that a lot of CO2 dissolves into the liquid, then once the pressure is released by one end of the bottle blowing, the CO2 will start to come out of solution, further raising the pressure. Another factor is that when one end blows off, conservation of momentum will cause the liquid inside to be hurled in the other direction. If the bottle was being held in place by something (not specified here), it seems like this could easily be enough force to blow out the other end. Looie496 (talk) 17:19, 26 April 2010 (UTC)

It is not a permanganate-acid reaction. Any reducible carbon compound (most of them are) such as sugar can be used, but some are better than others. The MnO2 is a staining solid. You could react permanganate with glycerin to produce gas, or just react baking soda with 10M hydrochloric acid. It will probably burst the bottle if you can find a way to detonate it once the lid is closed. It may be considered deflagrating though. --Cheminterest (talk) 22:21, 26 April 2010 (UTC)

This is the reaction that was going on:

12 KMnO₄ + 2 C₆H₈O₇ → 12 CO₂ + 2 H₂O + 12 KOH --Cheminterest (talk) 22:29, 26 April 2010 (UTC)

April 26

Stingray question

Do stingrays make a sound. I have looked extensively and have not found anything about stingrays making noises of any kind. thank you for considering this question. :)174.97.235.163 (talk) 00:45, 26 April 2010 (UTC)pat

Somehow I doubt it, as most fish don't (at least nothing we can hear). StuRat (talk) 00:51, 26 April 2010 (UTC)

Did you have something in mind, particular to a stingray? I used to have an electric catfish as a pet and it made lots of noise at night while electrocuting the minnows. Perhaps a stingray makes a sound (in the most general sense of 'making a sound') when it thrashes it's stinger into predator/prey...I mean, more so than a goldfish, let's say. DRosenbach ^{(Talk | Contribs)} 01:27, 26 April 2010 (UTC)

In this youtube video you can hear a clicking noise and you see a stingray: Octopus Attack - Fuertaventura 2009. Cacycle (talk) 06:53, 26 April 2010 (UTC)

Of course every type of fish makes sound as a result of water sliding over its body. When it comes to other types of sound, I wasn't able to find any reports in a quick Google Scholar search. There are apparently certain types of fish that "vocalize" by vibrating their swim bladders, but elasmobranches (sharks and rays) don't seem to be among them as far as I can tell. Looie496 (talk) 17:10, 26 April 2010 (UTC)

is there an exit valve? what about on the scuba fireman where? and on oxygen tanks in a ambulance or hospital?

Firemens SCBA apparatus.

where does the exhaled air go —Preceding unsigned comment added by Tom12350 (talk • contribs) 01:36, 26 April 2010

This question was answered above. Look for the section about 2-3 days ago labeled "scuba". --Jayron32 02:40, 26 April 2010 (UTC)

no they answered about scuba not scuba fireman where and on oxygen tanks in a ambulance —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:21, 26 April 2010 (UTC)

In a hospital or ambulance oxygen is normally given in two ways. In an emergency where a patient has collapsed and respiration is administered with a mask and pump bag the pump bag apparatus has an exit valve. When oxygen is given over a longer period with a light mask or little tubes at the entrance to the nose then the excess oxygen just dissipates into the atmosphere as there is no closed circuit to contain it. I suspect that the equipment used by firemen is similar in design principle to an underwater scuba, a closed circuit with a one-way exhaust valve. Richard Avery (talk) 07:21, 26 April 2010 (UTC)

On the side of the mask. See if this article helps: Firemens SCBA apparatus and and Oxygen maskAnd see diagram on the right --Aspro (talk) 07:23, 26 April 2010 (UTC)

And again, to be pedantic - the firemans' apparatus is an "SCBA" because the 'U' in "SCUBA" stands for "Underwater". SteveBaker (talk) 12:17, 26 April 2010 (UTC)

you say "light mask or little tubes at the entrance to the nose then the excess oxygen just dissipates into the atmosphere as there is no closed circuit to contain it."

but hows that because isint the mask tight? like is this pic  ?

http://thumbs.dreamstime.com/thumb_54/1145221626xhnGC8.jpg

or this

http://fransonchiropractic.files.wordpress.com/2009/04/oxygen20mask.jpg

or this

http://www.watersafety.com/rescue-and-response-equipment/images/4225023.jpg —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:07, 26 April 2010 (UTC)

milk

can buffered solutions like milk be used to naturalize acids or will it not work cause its buffered. —Preceding unsigned comment added by Tom12350 (talk • contribs) 01:55, 26 April 2010 (UTC)

So long as you don't exceed the buffer capacity of the milk, yes, it can be used to neutralize acid. The property of a buffer is that it works to neutralize BOTH acid and base (more properly, a buffer is something that maintains a constant pH with the addition of either acids or bases). See buffer for more info. --Jayron32 02:39, 26 April 2010 (UTC)

what is the "the buffer capacity of the milk" —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:20, 26 April 2010 (UTC)

Please start signing your posts by using four tildes like this: ~~~~. Please read the Buffer solution article for more info. A buffer is basically an acid and its conjugate base. That is, it consists of a pair of compounds that differ by a hydrogen ion, for example a solution that contained both acetic acid, HC₂H₃O₂, and the acetate anion, C₂H₃O₂^1- would be a buffer. It works because, by adding either acid or base, the conjugate acid/base pair works by reacting with either an added acid OR an added base, and so neutralizes either. Also, because the system is a dynamic equilibrium, the system obeys Le Chatelier's principle such that it resists all changes to return to its initial state. The buffer capacity merely means that the buffer only exists so long as both parts of the conjugate acid/base pair exist in the solution. If you add so much acid that you use up the base part of the buffer, then you no longer have a buffer, and you have exceeded the buffer capacity. --Jayron32 05:27, 26 April 2010 (UTC)

Additionally, you should probably also read up on Brønsted–Lowry acid-base theory which is the basis for understanding how buffers work. --Jayron32 05:30, 26 April 2010 (UTC)

i already read those. what is the "the buffer capacity of the milk" —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:35, 26 April 2010 (UTC)

I just explained that. A buffer consists of an acid and its conjugate base mixed together in water. If you add too much additional acid, you will consume all of the base, and thus destroy the buffer. --Jayron32 12:02, 26 April 2010 (UTC)

I'm not sure but perhaps the OP wants to know what the buffer capacity of milk actually is, not what it means. Having said that I wonder whether the OP actually properly understands buffer capacity or thinks it's a simple value that tells you precisely how 'powerful' a buffer is. In any case, the buffer capacity would vary depending on the type of milk I presume. Edit: These should provide a basic overview on what the buffer capacity of milk actually is [25] [26] [27]. Also [28] if you can find it. Nil Einne (talk) 12:32, 26 April 2010 (UTC)

With a complex solution like milk, it would be quite impossible to calculate directly. You could certainly do an experiment to find the value for yourself. You would need to titrate the milk dropwise with a strong acid, and track the effect of the added acid on the milk's pH. Then you would need to do the same experiment, but with fresh milk and a strong base. The resulting graphs should tell you roughly how much acid or base you can add before exceeding the buffering capacity of the milk. (after edit conflict) It looks like Nil Einne found the results of some of those experiments above. --Jayron32 12:46, 26 April 2010 (UTC)

Yes [29] is probably the most useful but needs a subscription. I have a tendency to reply and then search so often add my results after. I guess I should stop WP:AGF that the OP actually did a simple search before asking the question :-P Nil Einne (talk) 13:18, 26 April 2010 (UTC)

i dont need a exact value just a estimate. anyone know? —Preceding unsigned comment added by Tom12350 (talk • contribs) 21:56, 26 April 2010 (UTC)

From the article that requires a subscription: At pH7, the buffering capacity (dB/dpH) looks like it's around 0.02. It changes a lot depending on pH - eg. at pH 6 it's closer to 0.03. Aaadddaaammm (talk) 13:43, 27 April 2010 (UTC)

Source of pneumonia in bedridden elderly?

From what sources do the elderly often contract pneumonia? I'm thinking of bedridden individuals in nursing homes who are not likely to be able to spread it to other individuals in similar conditions, and who (because they're in the nursing home, not in hospital) by definition can't get hospital-acquired pneumonia. I don't see anything in our article that discusses the question, since it seems unlikely to me that the large number of elderly people who die from it are all infected with fungi, parasites, pneumonia-causing bacteria, or pneumonia-causing viruses when those around them don't have any of these problems. Nyttend (talk) 02:29, 26 April 2010 (UTC)

I think part of the problem is a lack of ability to clear the lungs while bedridden. Thus, any standard cold or flu can cause fluid accumulation in the lungs, which can suffocate the bedridden person. I am pretty sure that is the impression I get from the issue. I could be wrong though. --Jayron32 03:50, 26 April 2010 (UTC)

Also see the short article Aspiration pneumonia, which describes any non-infectious pneumonia caused by the inhalation of material, including one's own saliva and mucus. My guess is that this could explain many of these elderly, bedridden pneumonia cases. There's also Idiopathic interstitial pneumonia, "Idiopathic" being doctor speak for "We haven't the faintest clue what is causing this". --Jayron32 05:37, 26 April 2010 (UTC)

Hubble's "visible spectrum" image of the Carina nebula

I'm wondering what the moon, or the earth would look like if an image were compiled in the same way that the Carina nebula was. (wavelengths detailed here). Is it relatively simple to attempt this? 219.102.220.42 (talk) 02:30, 26 April 2010 (UTC)

If you could obtain the raw images taken at those wavelengths which record those spectral colours then yes. One could easily do the next stage of combining and balancing them in to one image. This image manipulation could be done with GIMP (which I have noticed the Jet Propulsion Laboratories in Pasadena have used) or Photoshop, etc. This web page explains in plain language, the technical bits about what needs to be recorded .Cameras and H-a Emission Nebulas. And what would Earth and the Moon look like? Well I sure: if people were able to mentally work that out, there would be no point using these imaging technique in the first place. However, the United States Geological Survey Spectroscopy Lab has some images of Earth. And the Jet Pro Lab has some images of the moon. [30] As always, Wikipedia has some articles:Imaging spectroscopy, Moon Mineralogy Mapper.--Aspro (talk) 08:00, 26 April 2010 (UTC)

Which elements do you want to use to make your images of the moon/earth? The picture basically shows areas where one element or another are more concentrated. If you use elements in the earths atmosphere, you'll have a white circle and nothing more, since those are basically perfectly mixed. If you choose elements on the ground, you'll see colors showing you where the elements you chose are more/less concentrated. Ariel. (talk) 08:05, 26 April 2010 (UTC)

Those nebula are emission nebulas wich emit light at particular wavelengths in a line spectrum. The earth and moon reflect are much more continuous spectrum, and so are not so easy to establish elemental composition by transition lines. In visible light what you see will be a good clue, eg yellow iron oxide, green chlorophyll. Graeme Bartlett (talk) 09:10, 26 April 2010 (UTC)

Dibenzodiazepines follow-up

I notice all the compounds listed in Category:Dibenzodiazepines are antiaromatic. So it must not be a coincidence. I guess the antiaromaticity destabilisation must not be very large? I'm curious about the relationship between conformation and agonism / antagonism of the target receptors. AFAIK lysergic acid compounds are planar ... right? Or are they? I notice some resonance structures are antiaromatic in LSD too. John Riemann Soong (talk) 03:24, 26 April 2010 (UTC)

What counts most for receptor binding are shape and charge. Antiaromaticity per se does not have a direct effect on binding (whereas aromatic rings allow for specific interactions such as pi stacking). Cacycle (talk) 06:49, 26 April 2010 (UTC)

Regarding LSD, the indole part is definitely aromatic. If you're considering "all the resonance possibilities" (treating them as distinct structures that contribute to the overall "real" average structure), you can mostly disregard antiaromatic ones if there are others that are aromatic. If you have an alkene or lone-pair or something that "maybe could resonate into a ring, but that would make antiaromaticity", that piece of the structure probably does not do that, and thus acts like an independent functional group. DMacks (talk) 08:47, 26 April 2010 (UTC)

Thanks... I was wondering because it doesn't appear to be a factor in LSD, whereas I can envision resonance structures in clozapine that would make it aromatic, not antiaromatic, e.g. by simply drawing benzene a different way. You know what I mean? John Riemann Soong (talk) 20:11, 26 April 2010 (UTC)

If you're interested in stereoelectronics in medicinal chemistry, you might like to get a good book on the topic, like this one, or search the literature. I did a quick Google search for "stereoelectronic QSAR" and found several interesting-looking articles, including Dynamic QSAR: A New Search for Active Conformations and Significant Stereoelectronic Indices.

Further Wikipedia articles of interest:

• Electronic effect
• Pharmacophore
• Quantitative structure-activity relationships

Books you could borrow from a library:

• A. J. Kirby (1996) Stereoelectronic Effects (Oxford Chemistry Primers)

Ben (talk) 19:16, 26 April 2010 (UTC)

Life expectancy of nuclear power plants.

What is the average life expectancy of a nuclear generating station? How do plants built in the US differ from ones overseas in terms of longevity? ataricom (talk) 05:00, 26 April 2010 (UTC)

According to Nuclear power#Economics, a reactor can last as long as 40-60 years. Dismas|^(talk) 07:27, 26 April 2010 (UTC)

Ant for ID

ID and extermination advice?

Hello! I must catch 10 of this type of ant everyday in my house. Is this a fire ant or a carpenter ant? What is the best way of getting rid of them, sort of calling an exterminator as a last resort? Could they be living outside my house in nests or in my house's foundation? I've found winged ants in my house, as well, which, as I understand, are the ones who help reproduce. Is that a bad sign? Any advice appreciated. Thanks.--el Aprel (^facta-_facienda) 08:17, 26 April 2010 (UTC)

If this was Australia I would say you had a sugar ant. Fill up all the holes they may come in through. You can spray poison around, but may poison you and may not last either. Graeme Bartlett (talk) 09:04, 26 April 2010 (UTC)

I'm not sure, but it does look like Camponotus sayi, red carpenter ant, to me. Red link for the red ant - isn't it ironic? Not really a harmful critter, there are much worse than it; but it can build nests (colonies) in wooden structures which is not something homeowners generally like. This article gives suggestions on how to deal with them, if that ant is really what I think it is. As I said, I am not sure. --Dr Dima (talk) 10:07, 26 April 2010 (UTC)

There are some more photos of Sayi on Wiki Commons [31]--Aspro (talk) 12:50, 26 April 2010 (UTC)

Thanks! Forgot to mention I live in Florida. Are Camponotus sayi ants common here?--el Aprel (^facta-_facienda) 19:30, 26 April 2010 (UTC)

No. Unless of course, their there on vacation. 'Florida' has however, narrowed it down a bit. Here's our next suggestion. Go to | Florida Ants. On the right hand column, under the heading 'Tools” is a link entitled - Florida ants in Google Earth. This link then gives you a map of which ants occur in which localities. I don't know how accurate it is but it looks impressive. In the mean time, see if they like water with some sugar added, because then use could try using borax.--Aspro (talk) 20:43, 26 April 2010 (UTC)

Did you mean to type "THEY'RE there on vacation"? Cuddlyable3 (talk) 23:45, 26 April 2010 (UTC)

• Mix a little jam with borax and smear it inside saucers, jar lids or the like, and leave them near where you find the ants. Replace daily. The ants come and eat the jam, and the borax poisons them. You get borax from places which sell old-fashioned cleaning materials (it's jolly useful stuff). DuncanHill (talk) 22:02, 26 April 2010 (UTC)

You could also get borax (sodium tetraborate decahydrate) at the grocery store. It is normally sold there for laundry freshening and a host of other uses. Are you sure you aren't talking about boric acid though? --Cheminterest (talk) 22:16, 26 April 2010 (UTC)

Not many grocers here sell borax anymore. I get mine at Boots the Chemists, and some old-fashioned hardware shops have it. Yes, I'm sure I mean borax. DuncanHill (talk) 22:32, 26 April 2010 (UTC)

I had a look at the "Florida ants" website, and think this is a Camponotus decipiens ant. I will try the borax solution. I remember treating another ant species, fire ants, with a powder poison that tricked worker ants to take back to their queen as food and exterminate the colony by killing the queen. Is there any poison like this for these carpenter ants? My guess is the borax solution only kills the ants that forage for it.--el Aprel (^facta-_facienda) 22:53, 26 April 2010 (UTC)

I think the powders of which you speak will contain borax or boracic acid. I've used the sweet borax mixture before, and after a few days what had been a steady stream of ants had reduced dramatically. DuncanHill (talk) 23:15, 26 April 2010 (UTC)

You will know if you have made the solution too strong because you will see dead ants. You want them to live long enough to get back and feed the others. The advantage of using borax has been already mention – its useful for so many other things and easier to buy.--Aspro (talk) 23:30, 26 April 2010 (UTC)

Mold

Is mold killed by pouring boiling water on it? 87.108.22.140 (talk) 09:02, 26 April 2010 (UTC)

Yes if you can heat it to close to 100 degrees. Eucaryotes are not good at surviving high temperatures. You may be left with a stain however. Graeme Bartlett (talk) 09:06, 26 April 2010 (UTC)

Thank you! I knew I could rely on Wikipedia! 87.108.22.140 (talk) 09:10, 26 April 2010 (UTC)

Also remember that mold is not just the blue stuff on the surface, but has hyphae in the material ti is decaying, you have to heat that too. And also mold may make poison in food, so don't just rely on boiling to make it fit for eating (if it is food). Graeme Bartlett (talk) 10:31, 26 April 2010 (UTC)

100 degrees C, right? Also, for what it's worth Aflatoxin is the stuff you still have to worry about even after the mold is dead. --144.191.148.3 (talk) 18:35, 26 April 2010 (UTC)

Yeah 100° F will just make it wet. Graeme Bartlett (talk) 21:44, 26 April 2010 (UTC)

Using a solution of sodium hypochlorite will kill mold too, and turn whatever it is poured on white. --Cheminterest (talk) 22:13, 26 April 2010 (UTC)

CCs?

Are CCs listed on Wikipedia?

eg, 10cc ( or 10ccs )

- 193.61.111.53 (talk) 11:15, 26 April 2010 (UTC)

Try HERE. Dolphin (t) 11:31, 26 April 2010 (UTC)

Unless you mean the music group, 10cc. AlmostReadytoFly (talk) 11:52, 26 April 2010 (UTC)

Also, see our orders of magnitude series entry for examples of things of a given volume: 1 E-5 m³. Paul (Stansifer) 12:17, 26 April 2010 (UTC)

Should I point out that this is probably a student of Loughborough College you're trying to get sense out of!--Aspro (talk) 12:21, 26 April 2010 (UTC)

Just to be explicit about it, when doctors on television say things like "10 ccs of adrenaline, stat!", the "cc" are an abbreviation for cubic centimeter, which happens to be the same volume as a milliliter. Other senses of the abbreviation can be found, not surprisingly, on the page cc. -- 174.24.208.192 (talk) 15:32, 26 April 2010 (UTC)

"Worst case of ice-cream induced brain freeze I've ever seen, administer 10 cc's of hot fudge, stat !" - Simpsons Ice Cream Social. StuRat (talk) 16:26, 26 April 2010 (UTC)

Another abbreviation for cc is cm³.--Cheminterest (talk) 22:14, 26 April 2010 (UTC)

Kepler mission field of view

Is it true that field monitored by NASA Kepler telescope roughly 24 times bigger then Moon angular diameter (as visible from Earth surface)? 70.52.182.184 (talk) 14:01, 26 April 2010 (UTC)

According to our article section Kepler_Mission#Mission_details its field of view is about 12 degrees. As the moons diameter is about half of one degree that seem to be about right.--Aspro (talk) 14:08, 26 April 2010 (UTC)

(EC) Kepler's field of view is approximately 10 degrees square. The moon subtends an angle of approximately 0.54°. So about 20x or so, yes. --Tagishsimon (talk) 14:10, 26 April 2010 (UTC)

Chromoscope pictures of the galaxy

on the site.. http://www.chromoscope.net/ when we observe the X-ray picture of our galaxy, we can see sumthing like the picture has been struck by a tiger paw or sumthing like that, like torn up in between, where none of the other images show such a thing. what makes it so? Prady —Preceding unsigned comment added by 116.73.242.109 (talk) 15:04, 26 April 2010 (UTC)

It looks like missing data. Dauto (talk) 15:39, 26 April 2010 (UTC)

Yes, it's missing data. This is more of a problem with X-ray telescopes because of their much narrower field of view. Other space telescopes do record the same thing, but over time they record the missing bits with a second or third pass. Why this happens can be understood if one just considers the sinusoidal curved black streak. This was the part of the celestial sphere hidden from the telescope by the sun. If you look at this website you will see an animate representation of the the celestial sphere. [32] Refer to the section: The tilt of the Earth's spin axis with respect to the ecliptic plane results in the Sun tracking out an seemingly sinusoidal path on the celestial sphere when viewed in the projection with the celestial equator horizontal. So, in short, the streaks and other black pixels are due to the fact that it is an incomplete scan of the of the celestial sphere.--Aspro (talk) 17:25, 26 April 2010 (UTC)

Who turns the machine off from a terminally ill patient?

If a decision was taken to turn the machines off, so that a terminally ill patient will die, who does physically push the button (or pulls the cable or whatever)?--Mr.K. (talk) 15:59, 26 April 2010 (UTC)

I'm guessing a nurse would do that. Dauto (talk) 16:00, 26 April 2010 (UTC)

That might make them legally liable, if it's later decided that proper authorization was lacking. For this reason, they may have the family member who requested that they "pull the plug" be the one who actually does it. StuRat (talk) 16:20, 26 April 2010 (UTC)

Do you have a reference for that? Matt Deres (talk) 16:56, 26 April 2010 (UTC)

(ec) Hmm. Do you have a source for that statement? It strikes me as very dubious. Looie496 (talk) 16:58, 26 April 2010 (UTC)

In general, a hospital's legal department would already have reviewed any request to "pull the plug" and certify that the requester has the proper authority and complies with any existing advance directives, etc. Once the lawyers sign off, I'd assume that the nurse is pretty well covered. Dragons flight (talk) 17:07, 26 April 2010 (UTC)

I do also believe that you if it is legally allowed (and it is), there must be a way of doing it without being sued for it. However, I am still not sure that a nurse will do it. Isn't it a huge psychological burden on a nurse, if she has to constantly kill people?Mr.K. (talk) 17:15, 26 April 2010 (UTC)

There are many psychological burdens in nursing. Compared to telling parents that their child has just died, removing a feeding tube from an unconscious person who is shortly going to die anyway is not that high on the list. Looie496 (talk) 17:38, 26 April 2010 (UTC)

I wouldn't say telling parents their toddler went to heaven is a heavier burden than actually killing someone. In the former case you can just use a euphemism and comfort yourself with the thought that it was unavoidable. In the latter case, Jesus, how can you don't think about what you are doing? Mr.K. (talk) 17:51, 26 April 2010 (UTC)

a) It is not up to the nurse/physician to tell parents their child "went to heaven". b) Turning off life support is distinctly different than "killing" someone. c) Don't assume for an instant that the doctors and nurses involved in the care of a terminally ill person do not think deeply about what is happening on a daily basis. Let's keep this discussion about facts and not emotionally charged rhetoric. --- Medical geneticist (talk) 22:59, 26 April 2010 (UTC)

I'm pretty sure you're all looking too much into this. The decision to pull the plug isn't made by the nurse, so they isn't responsible for the death even they did pull the plug physically. In the UK I think you need to have two consultant doctors who permit for life support to be switched off with the next of kin's consent, whereupon the nurse would switch it off. There is no real reason to feel guilt as I'm fairly confident the nurses will be of the same opinion as the doctors--that the person is dead anyway, merely being kept alive on machine. Regards, --—Cyclonenim | Chat  18:02, 26 April 2010 (UTC)

Besides which, there's always the possibility that the patient will stay alive even after the life support is removed... --TammyMoet (talk) 18:35, 26 April 2010 (UTC)

Not really. They go through thorough tests to make sure the person is really dead (which actually include disconnecting the machines for a while to see if the patient tries to breath on their own). While it is always possible that they have a mistake, the probability is negligible. --Tango (talk) 21:24, 26 April 2010 (UTC)

This is a reference desk. Please provide references when you give answers, instead of guessing. Here (page 4) is an article in which someone present at such an event wrote that a doctor and nurse were present, and the nurse switched off the breathing machine. Comet Tuttle (talk) 20:04, 26 April 2010 (UTC)

I second that. The first two answers were "I'm guessing" and sheer speculation. The original poster should look at the list of items under life support. Cessation of medical therapies (inotropes, total parenteral nutrition, dialysis etc.) are ordered by the physician. Feeding tubes and central IVs can be removed by nurses or doctors. Withdrawal of mechanical ventilation is performed by a respiratory therapist. Any of these steps would be discussed in detail with the next of kin or medical power of attorney. Hospital legal or ethical consultation would only be needed if there were a conflict between the medical team and the patient's family. --- Medical geneticist (talk) 23:11, 26 April 2010 (UTC)

According to this source (very small area is visible), the physician may also be the one to flip the switch. The book cited, Sourcebook on death and dying by James A. Fruehling seems like it would also be a good source regarding the possibility of a physician being criminally prosecuted in such an instance, though you'd need to purchase the book to find out for sure. Matt Deres (talk) 22:39, 26 April 2010 (UTC)

According to my wife (who used to be an operating department Nurse many years ago), any of the medical team might actually "flip the switch". The decision is the doctors' - but whoever happens to be standing next to the machine at the time might physically throw the switch - which could be the doctor, a consultant, a nurse, an OR tech or the anesthesiologist. It would be unlikely to be a relative or friend of the patient. She says it's like a prescription - the doctor takes the decision and is responsible - everyone else is just doing what they are told...following instructions...nothing more...it's just like administering any other treatment. Of course the actual making of the decision is an exceedingly complicated and legally 'careful' process involving lots of people. SteveBaker (talk) 02:47, 27 April 2010 (UTC)

No medical person would ever ever ever ask a relative to unplug a respirator. Horrible and cruel idea. Doctors or nurses do it when they are convinced that doing so is not killing the person since they are already dead. Often if any of the care team seem squeamish about it but do not actually oppose doing to, a more senior person will take the responsibility for flipping a switch. It isnt a daily event even in a busy ICU and it is treated seriously by those involved. And all institutions have careful brain death protocols with multiple tests and independent consultations. Been there done that. alteripse (talk) 04:00, 27 April 2010 (UTC)

Reactivity of Na or Ca

Is sodium or calcium more reactive? --Cheminterest (talk) 22:12, 26 April 2010 (UTC)

The elementary answer is at Reactivity series and boils down to "sodium". No doubt others will explain why my GCSE Double Science (which was the last time I heard of that) is inadequate and the question is really rather complicated. 128.232.241.211 (talk) 23:04, 26 April 2010 (UTC)

Yes, sodium is more reactive because it has only one electron in its outer shell, whereas calcium has two. Since sodium only has one, it is much easier to get rid of, making it more reactive. --The High Fin Sperm Whale 00:04, 27 April 2010 (UTC)

That's not actually a good explanation. Having more electrons in your shell increases electron shielding, causes things like spin pairing, etc. which actually makes electrons easier to get rid of -- assuming ENC is constant. The reason why sodium is more reactive than calcium is that calcium has an effective nuclear charge of about 2 while sodium only has an ENC value of around 1. John Riemann Soong (talk) 05:06, 27 April 2010 (UTC)

Both calcium and sodium metal are strong reducing agents: reactive enough to react with water. But compare the reactions: sodium vs. calcium. Buddy431 (talk) 00:41, 27 April 2010 (UTC)

Protein

1) What happens when someone does strength training and doesn't eat much protein afterward? How do the muscles repair themselves? Thanks. --Mudupie (talk) 23:33, 26 April 2010 (UTC)

Difficult to answer absolutely. What do you mean by 'much protein'? Lack of any nutrient will very likely lengthen post exercise recovery time. But more is not necessarily better.
Note that in the early stages at least, strength can increase without increase in muscle mass, as the muscles are learning the new 'skill' of lifting weights.

In the 'west' we tend to eat far more protein than we need. If you have a good all round diet, you may not need any extra protein. Which I cannot judge. This website here has figures that seem consistent with current nutrition standards (Please don't pay too much attention to the ads for 'protein powders' etc!).

This one at (Massachusetts General Hospital) is aimed at adolescents, Weight lifting and training, from which I quote: (my bolding)

"Since adolescents in the United States already eat a diet high in protein, there is no need for most adolescents to take protein supplements during weight training. And scientific studies have not supported any enhancement of muscle growth or strength from protein intake greater than the recommended amounts." para. 7, © 2010 Massachusetts General Hospital

• Recommended 'normal protein' RDA (Recommended Dietary Allowance) is 0.8 grams per kilogram of lean bodyweight (1 kilogram=2.2 pounds).
• If you exercise you need more.(Pregnant women need even more than weight lifters!)
• For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended.
  • I think many of us exceed that intake, whether we exercise or not.(see quote above)
• Too much protein can be bad for you (or give no advantage).[33][34]
• As is too little. see Protein-energy malnutrition

See also Body building#Protein, Protein (nutrient), Outline of nutrition, Nutrition, Human Nutrition, Diet (nutrition),and any related articles. This ref Desk question from about 3 day ago may interest breakdown of muscles.

Feel free to ask more questions if I have not fully answered your query --220.101.28.25 (talk) 12:22, 27 April 2010 (UTC)

Addendum: Don't take what is here as 'gospel' truth. I suggest you read the references here, or in the articles I have referred you to yourself. Also, for personalised nutritional advice, consult a nutritionist or dietician. --220.101.28.25 (talk) 13:33, 27 April 2010 (UTC)

American scientists recently advised all but some professional athletes to stop taking protein supplements. They are not necessary. Imagine Reason (talk) 14:27, 27 April 2010 (UTC)

That is one of the the points I was trying to get across, though I was assuming 'normal' amateur training. If you have a link to the data you mention I'd like to read it. :-) --220.101.28.25 (talk) 14:35, 27 April 2010 (UTC)

Soda Bottle Rocket

In science we are doing a project that involves us making rockets out of ordinary 2 liter soda bottle. We are allowed to modify the bottle in any way that we want. I could not find any information on how to find an ideal nozzle size for a given rocket. The wikipedia article on water rockets says that many people create a nozzle 9mm in diameter. I did not know if there was a means of calculating from chamber diameter, or more likely pressure (around one hundred psi in my case) what an ideal nozzle size would be. Additionally that 9mm nozzle is for a water rocket, and the means of propulsion for our rockets is compressed air. I was also wondering if anybody knew a way to connect two soda bottles, for added chamber volume, that could withstand 100 psi. If so, how should chamber diameter be proportioned to chamber length?

I think you need some water in there - it is the water being pushed out by the compressed air that propels the rocket. --Tango (talk) 23:53, 26 April 2010 (UTC)

We've got an article - water rocket, and if you google soda bottle rocket you should find lots of "how to" guides to help you. DuncanHill (talk) 23:56, 26 April 2010 (UTC)

100 psi is pushing it - these bottles are rated at 100psi and tested to 150psi when new...but this site says they may start to deform at 80psi when you have used bottle. So be really careful - stand well back - and FOR SURE don't be tempted to push it over 100psi! I strongly agree with DuncanHill - you need water as propellant if you want to make this thing really fly well. I don't see how using two bottles can help. You double the energy stored in the rocket - but you also double the weight (more than double it, probably because you've got to attach them together somehow. Real world rockets benefit from having multiple thrusters because they have payload other than the motors themselves...and even then, they used a staged approach where they drop the first stage motor before firing the second stage - so the second stage doesn't have to lift the weight of the first stage. Because you can't increase the volume - and you can't (evidently) change the propellant - so the trick is going to be to keep the weight down and to get the nozzle diameter right.

The scientific answer here lies in the "Tsiolkovsky rocket equation". It says that the 'delta-v' of the rocket depends on the log of (the mass of the fully fuelled rocket divided by the empty mass of the rocket) - multiplied by the exhaust velocity. Notice that the heavier the fully-fuelled rocket - and the lighter the empty rocket, the faster it will go. That's why you need some water in there...air at 100psi weighs very little indeed compared to a 2 liter soda bottle...so ln(m1/m2) is only a little bit bigger than zero. So you need a hell of a lot of exhaust velocity...so we're back to that nozzle again. Picking a decent nozzle is probably going to require some experimentation...there are equations, but they are touchy. The shape of the outlet matters in ways that are hard to figure out without supercomputers and such...so experimentation is the answer. SteveBaker (talk) 01:14, 27 April 2010 (UTC)

I second Steve Baker's "experimentation" suggestion. The trick is that you want to fill with enough water, and design the nozzle and air pressure charge, so that the air pressure equalizes at the exact instant that you run out of water. That way, you aren't carrying heavy, useless water around with you as inert mass. At the same time, if you put too little water in, and you have air pressure left over when all the water has already sprayed out, your rocket isn't making the most efficient conversion of potential energy (air pressure) into momentum. Swapping out nozzles is hard - so start with one rocket with a reasonable size nozzle; and vary your experimental parameters: quantity of water, and pressure of air added. Keep in mind that stored energy in this case is equal to pressure times volume - and the water isn't compressing. So, your total stored energy will decrease if you add more water (because you have less volume of air, so the P V product is smaller; but if you add water, your total momentum may increase because you have added mass. So, the question all boils down to: what is the optimum ratio of water to air to maximize the mass of water and its exit velocity, integrated over time? Try changing your parameters and experimenting and recording/graphing the data. When you have a lot of experiments, change the nozzle and see what changes. It's not likely that a mathematical treatment will actually be very useful here, because the messy parameterization details are so uncertain that even a computational solution would be prone to error. Nimur (talk) 14:24, 27 April 2010 (UTC)

April 27

Methanol poisoning

This might sound really dumb, but I thought ethanol was the only alcohol used in, well, alcoholic beverages. Since when is methanol used, or is not actually used at all and this incident rose from an accidental addition of methanol, instead of ethanol? Regards, --—Cyclonenim | Chat  00:30, 27 April 2010 (UTC)

The case you refer to appears to have involved the sale of adulterated Waragi. Methanol is not used, for exactly the reason that it tends to lead to illness and death. --Tagishsimon (talk) 00:37, 27 April 2010 (UTC)

Snowflake symmetry

Why do snowflakes form exactly the same on all sides? With billions of molecules between the edges, how does water freezing on one side affect the other side? Thanks in advance, --The High Fin Sperm Whale 01:55, 27 April 2010 (UTC)

Note that all crystals tend to be symmetrical, not just snowflakes. However, many do end up "deformed", too. StuRat (talk) 01:58, 27 April 2010 (UTC)

The edges in a snowflake do not affect one another. Rather the same thing is happening on both sides, so you get the same result on both sides. The shape is determined by things like humidity, wind, temperature, altitude, etc. And all of that is more or less equal on both sides. Ariel. (talk) 02:00, 27 April 2010 (UTC)

Then why don't you get a sphere instead of a crystal? --The High Fin Sperm Whale 02:05, 27 April 2010 (UTC)

They are not perfectly symmetrical. There are usually lots of asymmetries (which our pattern-matching human brains tend to ignore because we perceive the similarities as greater). The physics of snowflake formation (and symmetry) is complicated and not fully understood. It is clearly some kind of fractal process, though, which produce lots of (approximately) self-similar objects in nature. --Mr.98 (talk) 02:42, 27 April 2010 (UTC)

You can see pictures of snowflakes at Snowflakes and Snow Crystals. -- Wavelength (talk) 02:49, 27 April 2010 (UTC)

According to our snowflake article, "The sixfold symmetry arises from the hexagonal crystal structure of ordinary ice, the branch formation is produced by unstable growth, with deposition occurring preferentially near the tips of branches." You start with a tiny hexagon, and new water molecules, in order to fit in, have to continue fitting in to the crystal, maintaining the hexagon shape. But this doesn't explain why one end of a snowflake is similar to the opposite end of that snowflake, but different from other snowflakes.

Scientific American has an more complete explanation: the snowflake grows slowly, and at the same speed in all directions. The ambient temperature controls how the crystal forms and changes frequently, but (because the snowflake is very small) is always almost precisely the same over all parts of the snowflake.

Snowflake#geometry covers what effects the various temperatures have. Presumably, snowflakes grown in a lab at a constant temperature would all look boring. The shape of a natural snowflake reflects the history of its formation. If two snowflakes stay near each other throughout their formation, they should have a family resemblance. Very cool! Thanks for making me look this up. Paul (Stansifer) 04:59, 27 April 2010 (UTC)

Here is another SciAm explanation (which also points out that it is not entirely symmetrical)... my understanding (from a talk I saw not too long ago) is that physicists hotly debate this particular question, that it is not totally understood yet in a way that everyone can agree upon. --Mr.98 (talk) 13:33, 27 April 2010 (UTC)

FWIW here's a bigger hexagonal mystery. Cuddlyable3 (talk) 13:04, 27 April 2010 (UTC)

Mechanics of motion sensors

According to Hollywood Sign, the famous sign is surrounded by motion sensors that call the police when triggered. Assuming that this is true (the source doesn't say that), how would such a sensor be able to avoid false alarms from large animals (the source warns readers that if they ignore security and try to reach the sign, they're at risk of being mauled by mountain lions) and yet always catch humans? Nyttend (talk) 03:22, 27 April 2010 (UTC)

Motion sensors only detect motion. They can't distinguish between motion by a person and a large animal. Dolphin (t) 04:36, 27 April 2010 (UTC)

I suppose you could design an infra-red motion sensing system to look for a "mostly vertical heat sources", which are presumably human, since we walk on two legs. However, people could crawl on all fours to fool it. StuRat (talk) 05:45, 27 April 2010 (UTC)

If I were building it, I would attach the motion sensor to a video camera. Then I could look ahead of time before calling the police. Also, you can make barriers that work pretty well against animals, but that humans can defeat. Ariel. (talk) 06:01, 27 April 2010 (UTC)

The article Hollywood sign mentions a 1994 installation of a $100,000 security system featuring video surveillance and motion detection. Cuddlyable3 (talk) 12:41, 27 April 2010 (UTC)

Those that have read Dune (novel) will remember the Thumper which had the same cadence, as the Fremen of Arrakis and so was used to distract the worms. Well, back here on Earth, Remote Intrusion Detection Seismic Sensors can be designed to detect the human cadence (between 1 Hz and 3 Hz), and not the higher cadence of four-legged animals. Find a reasonable flat bit of path where the intruder can walk at a regular step ( flat sections are sometimes created to draw intruders to where you want them) and bury a device along there. You can purchase them with radio senders to report back. WP appears to have missed this application out on Seismometer and yet they are becoming quite widely used. Needless to say, the way to pass by undetected is to employ the same technique that the Fremen taught Paul. Here is an external link with more info: [35]--Aspro (talk) 09:04, 27 April 2010 (UTC)

I fixed your link to the Dune novel and not just a hill of sand. Cuddlyable3 (talk) 12:45, 27 April 2010 (UTC)

Thanks. Aspro (talk) 13:25, 27 April 2010 (UTC)

microbes outside earth

Does the search for life on Mars and other space regions include microbes, especially bacteria which live in any extreme conditions? Or is the search meant for humans? - anandh, chennai

They are definitely looking for microbes. There's little hope of finding humans on Mars, so they don't even look for that. StuRat (talk) 05:20, 27 April 2010 (UTC)

They may have found such microbes. The research is still very scanty due to the extremely small samples, and the very sparce evidence in those samples, but there possibility has not been eliminated in as many as three meteorites found on Earth which originated from Mars. See Mars_meteorite#Possible_evidence_of_life. --Jayron32 05:39, 27 April 2010 (UTC)

SETI activities seek life forms with human-like or better intelligence but generally assume they will not be found living on the planets or moons of this solar system. Lack of evidence has not hindered people imagining fictional Martians some of whom are not very nice.Cuddlyable3 (talk) 12:29, 27 April 2010 (UTC)

Sea blue - Sky blue

Why, at times, is sea-blue darker than the sky-blue when it is just a reflection of sky blue by the sea water? - anandh, chennai.

Water is not blue because of reflecting the sky, that's wrong. Water actually is blue, by itself, but so slightly that you need a lot of it to see the color. The deeper the water, the deeper blue it will look. Adding salt, as in ocean water, makes it more of a greenish-blue. StuRat (talk) 05:18, 27 April 2010 (UTC)

Thanks. colour of water is an interesting topic. 125.21.50.214 (talk) 05:51, 27 April 2010 (UTC)

THe colour of the sea here in England is usually grey most of the time, blue on sunny summer days, and rarely green. 78.151.102.119 (talk) 09:14, 27 April 2010 (UTC)

Since we know the colour of the sea isn't a reflection of the sky, but intrinsic to the water, I can only conclude that the bright blue or dull grey sky must affect the intrinsic colour of the sea by some unknown means. 81.131.28.200 (talk) 11:24, 27 April 2010 (UTC)

Well, everything is darker outside on gloomy cloudy days compared to bright sunny days. Is that what you're talking about? Zain Ebrahim (talk) 11:55, 27 April 2010 (UTC)

In a mirror or on the surface of a still lake viewed at a low angle the reflected sky is as bright as the sky. However some of the light falling on a sea surface is refracted into the water so only a part is reflected towards the viewer who perceives a dark and diffused (because of waves) image of the sky. Colour of water is relevant only to seeing a light source deep in the water. Cuddlyable3 (talk) 12:20, 27 April 2010 (UTC)

Human-Animal perceptions

If human perception varies from that of animal perception, say for example, in case of 'eye sight,' what exactly is the property (like shape, colour etc.,) of the entity (any object). Should we say that the object is rectangular,spherical etc., according to the human view? - anandh, chennai

I don't think we particularly care about animal perception, in general. Only animal researchers, trainers, etc., would care, as it affects their jobs. So, if a dog sees a globe, he probably thinks "uninteresting object" and doesn't attempt to classify it further, but so what ? StuRat (talk) 05:27, 27 April 2010 (UTC)

This is an extremely complicated, almost impossible question. The notion of property is a learned, acquired one. You learn what "round" or "straight" or "wavy" means when you see or touch it; you do not know if every human sees it the same way, but every (or almost every) human learn to associate those properties with the same categories. Now, when people study the anatomy and physiology of the eyes, lateral geniculate nucleus, and visual cortex of humans and Old World primates (Catarrhini), it turns out that the structure and function is fairly similar (size and exact shape notwithstanding) across individuals and even across species. This allows one to argue that humans, chimps, and macaques really see those things the same way. Now, cats or rats have eyes and brains that are less similar to ours; birds, reptiles, and fish are further yet; and insects with their compound eyes and ommatidia-lamina-medulla-lobula early visual processing pathway are nothing like the humans at all. Yet bees can be taught to distinguish shapes, and even properties of shapes, such even as the abstract notions of "sameness" and "difference". Do they see the same way as we do? No. --Dr Dima (talk) 07:52, 27 April 2010 (UTC)

An even more puzzling to our hopelessly anthropocentric perception is the question of what qualia (if any) does a rodent have when it "sees" objects with its whiskers (vibrissae); or a pit-viper has when it "sees" objects with its heat sensing organs, or a bat when it "sees" objects with its ears. --Dr Dima (talk) 08:04, 27 April 2010 (UTC)

Well, if you look at the center of a flower you may see a half dome where a bee might "see" a star shape http://en.wikipedia.org/wiki/Bee_learning_and_communication#The_Neurobiology_of_Color_Vision However, that would assume that the bee interpreted the visual information it gets the same way a human with a "bee eye camera" would. IMHO that is highly unlikely. I've linked this story before, but it shows that even an untrained human brain has trouble interpreting shapes. http://nfb.org/legacy/bm/bm02/bm0211/bm021105.htm 99.11.160.111 (talk) 08:57, 27 April 2010 (UTC)

Yes we should OBVIOUSLY say that an object is rectangular, spherical etc., according to our human view. Cuddlyable3 (talk) 12:09, 27 April 2010 (UTC)

Ambidextrous people

how better are ambidextrous people in terms of intelligence, compassion etc.,than a left-hander or a right-hander, while the ambidexterity is obtained either by natural or acquired ways? - anandh, chennai

I would suspect you'd find them midway between "right-brain" and "left-brain" individuals, so be able to integrate logic and emotions. StuRat (talk) 05:29, 27 April 2010 (UTC)

While Lateralization of brain function is a real thing (certain tasks predominate in certain areas of the brain) the whole "artsy people are right-brained and scientific people are left-brained" is mostly pseudoscientific bull crap. There's no hard evidence that things like personality or aptitude is connected in this way to "brainedness". --Jayron32 05:36, 27 April 2010 (UTC)

Nope, I'm just as daft as everyone else :-)) 99.11.160.111 (talk) 08:58, 27 April 2010 (UTC)

The Wikipedia article Ambidexterity is mostly about performance in sports. Cuddlyable3 (talk) 12:05, 27 April 2010 (UTC)

What is this box?

There is a large blue metal box in the office in which I work. The footprint is about 8'x3' and it stands about 6' tall. There is a white box on the outside (maybe 2"x6"x10") with two pressure gauges attached. This white box also has a temperature gauge that goes from 50 to 100 degrees F. There is also an electrical junction box on the outside with a big handle type on/off switch. Next to that is a card which is dated from 1999 which lists when various PMs were done. Notes for those PMs include mentions of replacing or checking tension of belts and greasing motors. In black permanent marker, someone has written on the side of the blue box, "CYMER". I have no idea if the writing is in any way related to the box. The only identifying marking is a logo which I've taken a picture of. I ran the image through TinEye and it didn't come up with anything.

The office in which I work used to be a lab of some sort but it was converted to an office years before I got my current job. None of my co-workers know what this box is and we're all kind of curious what it is and/or what it did. I work in the semiconductor industry if that helps. Anyone know what I've described? I'm putting this question on this desk since the room used to be a lab and this box might have been used for something in that lab. Dismas|^(talk) 08:32, 27 April 2010 (UTC)

I don't know what the box is, but you should also take a picture of the whole box from a number of angles. Did you try opening it? Does it make noise ever? Ariel. (talk) 09:37, 27 April 2010 (UTC)

Cymer, Inc.'s website [36] describes the company as a supplier of excimer light sources for photolitography. Pictures of their equipment suggest it fits the general dimensional description you gave, although none of the pictures on their website shows a blue housing. This U.S. patent [37] may provide some clues to the presence of a temperature gauge and a motor. --173.49.9.93 (talk) 09:42, 27 April 2010 (UTC)

It's been powered off ever since I've been in here (about 7 months). So, no, it's never made any noise that I know of. Considering the "L" logo, I don't think it's a Cymer product. There is nothing to open. The outside is just blue sheet metal. I don't see any access panels. One of the blue panels has had a couple screws removed but considering the 8' length and the fact that I don't have any business poking around in the box, I don't feel comfortable trying to pop the panel off if it will indeed come off. My work has nothing to do with it, so it would be rather embarrassing if I couldn't get it back together again. Dismas|^(talk) 10:03, 27 April 2010 (UTC)

Inside you might find a pre-193nm laser with cooling apparatus as it might be cheaper to leave useless technology in place when there is a radical change in node size as it evolves. Currently the plan is to shift to EUV for manufacture below the 17nm node when the power of EVU is able to match that of current 193nm lasers. Your box probably contains a light source for manufacture of older and larger node sizes of very long ago. I would consider it a showpiece in that case like the MARK I computer at Aiken Lab and care for it like a baby and show it off to friends. Plain vanilla with chocolate chips (talk) 11:23, 27 April 2010 (UTC)

Think we need more info. What is the range of the pressure gauges. It sound like it could be a compressor but compressors often run hotter than 100 deg F. Stand on some steps and see if there are any vents or disconnected pipe work on top. Are the pipes iron, stainless steel or copper? If pipe were at one time attached, there may still be the signs of pipe brackets on the ceiling and walls. Are there any vents, what shape? Any more signs on roof of box. Any inspection or access panels up there?. How are they fixed and are lead seals attached (or bits of twisted wire where they once where). Can you follow the cable from the switch box back to the main switchboard for that floor. It maybe that the electrician labelled what piece of equipment was on that circuit. The company you work for will have a department responsible for looking after the building(s) itself. They will have records of all plant and equipment that is permanently installed. I have found a good approach for eliciting a response from such departments in a reasonable time is too say to them: “Is this large equipment cabinet still used or important? Because we are just about to drill a large hole through it!” A manager or executive officer ( or maintenance guy) should know the name and how to contact this department. Maybe their listed in the internal telephone directory under “Site Management or Estates Management or Work Engineering Department, etc. Do however, steer clear, of involving the PHB. Lastly, I would consider that unknown cabinet could well be a safety issue, for one is just trusting someone else did their job properly and ensured that there are no hazardous materials left in side.--Aspro (talk) 11:10, 27 April 2010 (UTC)

The "L" graphic may or may not be the manufacturer's logo. It seems to communicate something about liquid and temperature. Just a guess. --173.49.9.93 (talk) 12:20, 27 April 2010 (UTC)

Wow, what a bit of history! I work for what became of the company that made that. The "L" graphic is actually a really really old Liebert Corp. logo. If you do a google images search you can see what the latest incarnation was (before they stopped using the logo altogether about 2 years ago.) What you are looking at is probably some sort of industrial chiller, installed to provide cooling for the Cymer device that someone else described. --Jmeden2000 (talk) 14:46, 27 April 2010 (UTC)

Could be -well done! The logo symbol does remind me a bit of a Dewar flask with a thermometer stuck in it (the pressure gauges for first and second stage compression maybe). Anything like that (including a compressor) is going to need loads of cooling though. I'm not going to speculate more without more info – it like clutching at straws. After all, it might just be something very obvious; like the new Doctor has almost fixed the Chameleon circuit and the logo is just part of its disguise – but its still suck at blue! --Aspro (talk) 14:57, 27 April 2010 (UTC)

Light-straight line; but how many?

It seems to be a ridiculous doubt. Light travels in a straight line. How do we measure/count the total number of 'straight lines' in a particular 'lighted' region? - anandh, chennai

Just because something travels in a straight line, does not mean that it is a line. Lux and candela are used to measure light intensity, if that's what you're after, though I don't know much about them. Vimescarrot (talk) 10:55, 27 April 2010 (UTC)

{ec)If I understand our question, the answer is, we do not tend to count such things. An illuminated area is being bombarded by photons. The path of each photon can be considered to be a straight line. If you consider the very smallest point of an area being illuminated, there will be countless straight lines connecting that point to the source of illumination - such as the sun. Trace all of those lines, and you get a solid cone made up of countless lines, with the illuminated point at one end, and, for instance, the sun at the the other end. --Tagishsimon (talk) 10:58, 27 April 2010 (UTC)

The path of each photon is a wave. For example, in the double-slit experiment, the photons each travel through both slits. — DanielLC 14:52, 27 April 2010 (UTC)

Is the question "is space infinitely divisible"? 81.131.28.200 (talk) 11:40, 27 April 2010 (UTC)

A true line is an abstract thing with zero cross-sectional area. You could not make holes small enough in two walls some distance apart for a light beam passing through both holes to be reduced to a "line". Questions about how many infinitesimal quantities can add up to a finite quantity, such as how infinitesimal spots lit by lines of light can illuminate an area, are answered mathematically in integral calculus. Before calculus these subjects seemed paradoxical. Cuddlyable3 (talk) 11:47, 27 April 2010 (UTC)

1) Light only travels straight in the absence of gravity. The stronger the gravitational field, the more the path of the light will be bent. (There is an alternate way of looking at it that has the light straight and space-time curved, if you prefer that model.)

2) Light has a dual wave/particle nature. The particle models does have photons of finite size, so there would be a specific, very large, but not infinite, number of photons flying in any given room. StuRat (talk) 13:38, 27 April 2010 (UTC)

penury

Is the a mental disease characterized by penury? Plain vanilla with chocolate chips (talk) 10:53, 27 April 2010 (UTC)

No. Mental disease may lead to penury, but is not characterised by it. --Tagishsimon (talk) 11:00, 27 April 2010 (UTC)

penury noun: a state of extreme poverty or destitution. Cuddlyable3 (talk) 11:34, 27 April 2010 (UTC)

It's a pretty inevitable result of schizophrenia in the US. alteripse (talk) 12:06, 27 April 2010 (UTC)

Only if their family won't/can't take care of them. Dauto (talk) 14:30, 27 April 2010 (UTC)

Spiders

What is the biggest spider found wild in the UK? Is it rare? If so, what would be the largest commonly encountered spider? I'm talking in terms of legspan here, although it would be nice to know the largest in terms of mass also. Thanks