Wikipedia:Reference desk/Archives/Science/2011 October 24

= October 24 =

Reptile heat source
Do I really need to buy the $12.95 pet shop light bulb for my ball python or can I just get a Shoprite incandescent 4-pack for $1.99? UV-A and UV-B ehh...  DRosenbach  ( Talk 00:13, 24 October 2011 (UTC)
 * Hello old chap - this link seems to have a lot of information about lighting, heating and different bulb types - . Quintessential British Gentleman (talk) 00:20, 24 October 2011 (UTC)


 * (ec) If you need UVA and UVB, your standard incandescent bulb (even "full spectrum" ones) will not be sufficient. Here is a nice page that goes through all of the different lighting options and what they do and don't produce for your pet. It strikes me that trying to be cheap in this department will negatively affect your pet. --Mr.98 (talk) 00:21, 24 October 2011 (UTC)


 * Please make sure to use the correct light, no matter what you pay. I work with shelter/rescue groups that often take in various reptiles that haven't been cared for correctly, including the wrong or no light source.   Bad things can happen for the animal if something as seemingly simple as light is not given to the animals.  Dismas |(talk) 12:56, 24 October 2011 (UTC)
 * But it was explained to me at the pet shop that I don't even need a light -- I could have chosen a heat pad instead of a warm bulb, and that doesn't provide any UV light.  DRosenbach  ( Talk 01:52, 25 October 2011 (UTC)

Giant human skeleton
Are there any reliable sources for those pictures, ?--82.114.165.50 (talk) 02:00, 24 October 2011 (UTC)
 * No. L ANTZY T ALK 02:30, 24 October 2011 (UTC)
 * Snopes and the National Geographic cover some similar photos. Please note the reference to the square-cube law at the bottom of the Snopes article, and the links in the square-cube law article that show that if there ever would be giants like that then they wouldn't just look like scaled-up versions of humans.Sjö (talk) 05:17, 24 October 2011 (UTC)

Thanks a lot. What I want to understand is if such photos/articles are logical or just hoaxes as usual. Is there any Wiki article expressing similar material? To be more specific, I'm eager to know about human height history since their ancestors.--Almuhammedi (talk) 12:54, 24 October 2011 (UTC)
 * The human height article may be of interest to you. Dismas |(talk) 12:58, 24 October 2011 (UTC)
 * Thanks Dismas. That article seems to be focusing just on the history of past few years. If you look at this site,, you will find some exaggerated figures and I need to know if it were true and what reliable sources can also show this.--Almuhammedi (talk) 13:41, 24 October 2011 (UTC)
 * See also gigantopithecus. ~ AH1 (discuss!) 14:37, 24 October 2011 (UTC)
 * The site you linked to is unusually bizarre Creationist nonsense. It has nothing to do with actual science. --Mr.98 (talk) 02:22, 25 October 2011 (UTC)

breast cancer risk
Celibate and childless women are thought to be at greater risk of breast cancer. Is this because childbirth boosts the mother's immune system, and if so what is the mechanism?Pensioner.bsc (talk) 02:01, 24 October 2011 (UTC)
 * Does lactation change the susceptibility of breast tissue to cancer? 67.6.179.27 (talk) 02:38, 24 October 2011 (UTC)


 * There is an apparent correlation between menstrual cycles and breast cancer. Having children reduces the total number of menstrual cycles, which reduces the risk of breast cancer due to the correlation. -- k a i n a w &trade; 02:44, 24 October 2011 (UTC)


 * As for the question by 67IP: yes, lactation triggers changes in the breast tissue that make it less susceptible to cancer. 67.169.177.176 (talk) 05:48, 24 October 2011 (UTC)

-

→ Σ  τ  c. 04:59, 25 October 2011 (UTC)

A censor has removed the discussion on this subject, it was meant to be a scientific question, not a personal medical question. I don't suffer from breast cancer myself, as it is not common in men, but many women do, and sensible discussion on how to minimise the risk should be encouraged, not censored. Pensioner.bsc (talk) 14:24, 25 October 2011 (UTC)


 * I restored the top part of the discussion. Once it went into a person asking specifically how to control his/her (but likely her) risk of breast cancer, that is medical advice. It should not be asked here and cannot be answered. -- k a i n a w &trade; 14:46, 25 October 2011 (UTC)


 * Despite the phrasing of that question "Is that what women doctors advise?", it is actually not a request for medical advice to ask what doctors advise as an announcement to the general population. We see those all the time - cut cholesterol, keep blood sugar low, etcetera.  But to avoid further debate I'll rephrase the last question in academic terms:


 * Do pills for menstrual suppression or for artificially induced lactation reduce breast cancer risk? (Pensioner.bsc (talk) 21:12, 24 October 2011 (UTC) as rephrased by Wnt (talk) 15:06, 25 October 2011 (UTC))


 * That's OK, perhaps I shouldn't have mentioned the word "doctor", which triggered alarm bells!Pensioner.bsc (talk) 17:54, 25 October 2011 (UTC)


 * This is a huge topic and I'm just poking a pile of literature and reading what falls off the top. But for example,  speculated in 1992 that a birth control regimen might be devised to reduce breast cancer along with ovarian and cervical cancer; nonetheless estrogen and progesterone (in older women) can generally have an effect of increasing breast cancer risk  and is "positively dependent on oral contraceptive use" .  While the intended effect of contraceptives raises breast cancer risk, the fact that they increase it in older women makes me think it's more than that.  After all, breast cancer has a strong association with estrogen in general. Wnt (talk) 15:18, 25 October 2011 (UTC)


 * I've looked a little into the other question about induced lactation, but it's hard to find much about it in the scientific literature. If someone has done a study of breast cancer in wet nurses or women who practice erotic lactation in the long term, I didn't see it.  I didn't see anything about domperidone and breast cancer.  Bitter melon (Momordica charantia) is reputed to help lactation and might help against breast cancer  but the evidence is very sketchy and the mechanism might not be this.  I'm afraid I don't have a proper answer here. Wnt (talk) 17:18, 26 October 2011 (UTC)

To get some references down here, I made the quickest possible riffle through PubMed, to the beginning of page 5 of 12 out of "breast cancer childbirth". Late age at first full term birth (>30 yr) increased odds of lobular breast cancer in one study by 2.4-fold, and other types by 1.2, 1.3, and 1.7 fold. ( and also ). Another study found association of childbirth with breast cancer but not significant evidence that breastfeeding time was correlated  Perhaps mammary differentiation during pregnancy reduces breast cancer risk - but in mice, blocking that with dioxin slowed cancer formation after induction with a standard lab carcinogen   (I wonder how all this reconciles with a statement that abortion does not increase risk of breast cancer... )  Note also that there is a higher transient risk of breast cancer for a few years after pregnancy, which correlates a little bit with IGF-1 level and size of the infant (see  and some references I didn't bother to paste). Wnt (talk) 15:21, 25 October 2011 (UTC)


 * Thanks for the refs, as you say a huge topic, and a lot of people working on it. As I saw somewhere in the refs, historically women would be free from menstruation for long periods while pregnant or breastfeeding, and did not live so long. So if too many menstruations in modern women does increase the risk, it would seem sensible to space them out to quarterly instead of monthly. Complete suppression might be a step too far with unknown side effects.Pensioner.bsc (talk) 18:21, 25 October 2011 (UTC)

What color would the moon be
if it was seen from space, under pure white light, and the reflected light was averaged? With what shade does it tint the sunlight it reflects, and how strongly? Card Zero (talk) 12:22, 24 October 2011 (UTC)
 * Under visible light, there isn't really a preferred color, or specific wavelength where the Moon exhibits an unusually high reflectivity. The surface is pretty much shades of gray, just as it appears in photographs taken from space.  This article about the color of the moon addresses the point directly; our article on the geology of the Moon will tell you what the surface rocks are made of. TenOfAllTrades(talk) 13:21, 24 October 2011 (UTC)
 * I found that Universe Today article already, but didn't have complete faith in it because it links to a page which it says "explains how to get the right color of the Moon in Photoshop". That page in fact is about how to get the wrong color of the moon in Photoshop, by adjusting levels so that the moon appears on average white, and then increasing the saturation of what's left - it's about making a kind of false color image. However, if you agree that it's gray, too, I'll go along with that part. Card Zero  (talk) 13:30, 24 October 2011 (UTC)
 * Remember, though, that various minerals on the Moon including anorthosite may have tints that are locally shades other than gray. ~ AH1 (discuss!) 14:35, 24 October 2011 (UTC)
 * I am at a loss for a reference, but I want to say that it was during the Apollo 15 lunar excursion that the astronauts discovered one incredibly out-of-place bright orange rock. I seem to recall quite a scientific hullabaloo over this one lunar sample, debating whether it had formed in-situ, had ejected during an impact, or had deposited from space... but in any event, it was the only very non-grayish sample obtained on any of the missions.  I will try to track down exactly which mission discovered this sample.  Nimur (talk) 06:12, 25 October 2011 (UTC)
 * Ah, here we go: Orange Soil near Shorty Crater, discovered on Apollo 17. It is called a volcanic glass on this particular NASA page. Unfortunately, with only a few data-points of manned exploration, we don't really know how rare this stuff is on the lunar surface.   Nimur (talk) 06:15, 25 October 2011 (UTC)
 * More information from astronaut Harrison Schmitt, the first and only scientist (a geologist) to walk on the moon: "The Missions of Understanding," ... "Finding orange soil near Station 4 on Apollo 17 at the time when oxygen was running low kept us on the jump. We dug a trench 8 inches deep and 35 inches long, took samples of the orange soil and nearby gray soil...." This link includes more high quality, better true-color photos (including some from the Hasselblad camera), and some micrographs of samples that were brought back to Earth laboratories. An entire chapter in this book is dedicated to Beads of Orange Glass.   Nimur (talk) 06:21, 25 October 2011 (UTC)

Blue sky
Is it possible that the blue color of the sky has something to do with the water color reflection on the ozone layer? Some friends of mine seem not convinced with Rayleigh scattering and wanted me to further search about, reasoning that photos by satellites don't show enough blue color for land hemisphere.--Almuhammedi (talk) 13:01, 24 October 2011 (UTC)


 * No, it is not possible, why is the sky blue everywhere then? It is certain to be Reyleigh scattering, blue light is scattered more than red light as it has a shorter wavelength, and it has a shorter pathlength. At dusk and dawn, all blue light is scattered, and red light is seen, even though it hasa longer pathlenth. Plasmic Physics (talk) 13:50, 24 October 2011 (UTC)


 * Could the overland sky be less blue due to dust storms? ~ AH1 (discuss!) 14:33, 24 October 2011 (UTC)


 * Yes, it can. Plasmic Physics (talk) 22:07, 24 October 2011 (UTC)

Ice
why is ice slippery? — Preceding unsigned comment added by 203.112.82.2 (talk) 15:54, 24 October 2011 (UTC)


 * Ice is only slippery when it has water on the surface. Water acts as a lubricant. When ice is very dry, it is not slippery. However, it takes very dry and very cold air to produce ice that doesn't have a layer of water on the surface. Even pressure from standing on ice will cause it to produce a thin layer of water. -- k a i n a w &trade; 15:58, 24 October 2011 (UTC)
 * According to the academic genius of cracked.com this is disputed, here. Here is a NY times covering much of the same ground. There is no clear answer. Grandiose (me, talk, contribs) 16:24, 24 October 2011 (UTC)


 * Good articles. I'd like to invite them to northern Norway in February and ask them to try to slip on the ice. This is one of those things where scientists are stating one thing and people on the ground are walking around on non-wet ice (I'm avoiding the use of "dry ice") and noticing that it isn't slippery. -- k a i n a w &trade; 16:38, 24 October 2011 (UTC)


 * Northern Norway doesn't get nearly cold enough in winter for this to happen -- even Tromso and Hammerfest hardly ever get colder than about -15 C. Now, if you invite your friends to some place like Vorkuta or Norilsk, then it's a different story altogether.  Us Russians got antifreeze for blood... :-) 67.169.177.176 (talk) 04:39, 25 October 2011 (UTC)


 * There's not much snow in Tromso - kept too clean. Up the mountains - which is where I was stationed - it is all ice. Never slipped once. Then, took a ride to the airport to fly home. Slipped about 20 times walking from the airport to the plane. -- k a i n a w &trade; 16:28, 25 October 2011 (UTC)


 * Please keep in mind that it's always colder in the mountains than in Tromso itself. 67.169.177.176 (talk) 01:03, 26 October 2011 (UTC)


 * Point Barrow would also be a good place to demonstrate the non-slipperiness of ice in extreme cold conditions. 67.169.177.176 (talk) 05:29, 25 October 2011 (UTC)


 * From personal experience, clean ice is definitely still slippery at -25 C. Dragons flight (talk) 16:02, 25 October 2011 (UTC)


 * This means that in the city of Tromso, ice is always slippery because it never gets below -18 C. In Vorkuta, on the other hand, -40 C is commonplace and -50 is not unheard of, and Norilsk is colder still, so in those places you could walk on ice and not slip. 67.169.177.176 (talk) 01:07, 26 October 2011 (UTC)


 * The article Ice on wikipedia also says that your explanation is in doubt. — Preceding unsigned comment added by 203.112.82.1 (talk) 17:18, 24 October 2011 (UTC)

The surface of a piece of ice is always liquid, even at absolute zero. This fact and not that ice melts under pressure, is now believed to be the cause of ice being slippery. Count Iblis (talk) 17:13, 25 October 2011 (UTC)


 * So then, could you explain why ice ceases to be slippery at extreme cold temperatures (as Kainaw testified from personal experience, and as every bush pilot knows)? 67.169.177.176 (talk) 01:09, 26 October 2011 (UTC)


 * It's to do with contact - as soon as contact is made, the thin layer of water is no longer a surface, but an interface between two solid objects. This means that the layer of water at the interface, solidifies, and bonds the two objects together. This is true for any temperature at which ice is stable. The time it takes for the water layer to freeze and weld the ice to the touching surface is a function of time. The colder it is, the less time it takes to weld. The reason why why ice is slippery at relatively higher temperatures, is that it simply hasn't had the time weld together. You'll find that if you have a metal disk or other wise good thermal conductor, it will easily slide along on a flat sheet of ice. However, take that same disk and rest it on the ice for 5 minutes, and you'll find it stuck to the ice. Plasmic Physics (talk) 02:14, 26 October 2011 (UTC)


 * This is really under the domain of nanoscience. Plasmic Physics (talk) 02:17, 26 October 2011 (UTC)


 * Related to that answer is just how cold it was when I was in the Norwegian mountains and didn't slip. I was trained to use duct tape to seal up my tent. I couldn't. The glue on the tape froze before I could get it to stick to anything. I don't know the actual temperature because I only had a mercury thermometer and it went "mushy" on me. I figure it was close to -35c if not colder. So, I believe that any water on the ice would nearly instantly freeze. -- k a i n a w &trade; 02:24, 26 October 2011 (UTC)


 * Your report of the mercury getting "mushy" indicates that the temperature was close to -40 C (but not quite there). 67.169.177.176 (talk) 02:44, 26 October 2011 (UTC)


 * We just established that the thin film of water does not freeze, as long as it is on the surface and exposed, doesn't matter how cold it is. Regardless, it may have more to do with the glue being affected by the temperature than the ice. Plasmic Physics (talk) 02:51, 26 October 2011 (UTC)

How can a particle be its own antiparticle?
For composite particles like mesons, it makes sense, but for elementary particles with no apparent internal structure, it doesn't seem right, yet it seems that this is the case for all bosons (except the W boson). How does annihilation work in these cases? --Goodbye Galaxy (talk) 16:21, 24 October 2011 (UTC)
 * The article Antiparticle indicates that for particles which are their own antiparticle will annihilate when they interact with another of their kind. Such particles obey a certain equation known as the Majorana equation which explains their behavior (well, it would explain it to someone who understood it, which I do not).  -- Jayron  32  17:41, 24 October 2011 (UTC)


 * Jayron, the Majorana equation can only be used for fermions. Bosons will follow either a real Klein–Gordon equation if they have spin zero or a real vector boson equation if they have spin 1.By real I mean no imaginary numbers. If imaginary numbers are allowed than the particle and anti-particle equations are related to each other through complex conjugation. Dauto (talk) 18:20, 24 October 2011 (UTC)
 * Just adding a link to the Proca equation which is the spin-1 vector boson equation I was talking about. Dauto (talk) 18:35, 24 October 2011 (UTC)
 * That's good Dauto. You should fix the lead to the antiparticle article, because it implies that all particles which are their own antiparticle follow the Majorana equation.  I was only reporting what I was told.  -- Jayron  32  19:38, 24 October 2011 (UTC)
 * I removed the mistaken reference from the article. Dauto (talk) 17:04, 25 October 2011 (UTC)
 * So photons annihilate with other photons? Does this happen all the time? What do they annihilate into? More photons? --Goodbye Galaxy (talk) 18:05, 24 October 2011 (UTC)
 * Yes, photons can annihilate into more photons. It is called scattering of light by light - A purely quantum phenomenon absent from classical physics. Dauto (talk) 18:08, 24 October 2011 (UTC)


 * Although photons don't couple directly, they can interact through higher-order processes. See Two-photon physics.  Red Act (talk) 19:40, 24 October 2011 (UTC)
 * (EC)Pick up a pair of gloves. They're mirror images of each other. One is the particle and the other is the anti-particle. Which one is the particle and which one is the anti-particle? It's just a matter of arbitrary convention. Now pick up a pair of socks. They still can be seen as mirror images of each other except that they are completely identical. The particle and anti-particle are one and the same. What that means is that two Z-bosons (for instance) can annihilate each other. Dauto (talk) 18:06, 24 October 2011 (UTC)

Now my feet are cold. Thanks for the explanation! --Goodbye Galaxy (talk) 18:35, 24 October 2011 (UTC)
 * In fact there is a reason for calling some particles "particles" and their CP-transformed brother particles "anti-particles" and not the other way around. In the universe there is more matter than anti-matter, which has something to do with the CP-violation. So one calls the normal type of matter "matter" and the other type, from which there is nearly nothing, "anti-matter".--Svebert (talk) 17:03, 26 October 2011 (UTC)


 * Yes, that's the criterion generally adopted. But that's still an arbitrary choice and occasionally it is convenient to use other criteria. Dauto (talk) 21:37, 26 October 2011 (UTC)
 * Its the same, matter adn anti matter , Its jast revers in time   . thanks Water Nosfim

bird "song"
most of the birds I've seen make sounds that are too short (and repetitive) to be called "songs" are there any birds that really "sing"? like... making a melody or something? — Preceding unsigned comment added by 31.7.57.246 (talk) 18:58, 24 October 2011 (UTC)
 * How about this blackbird song, from our bird vocalization article: Looie496 (talk) 19:10, 24 October 2011 (UTC)
 * Come to Australia and listen to our magpies. HiLo48 (talk) 19:44, 24 October 2011 (UTC)

I am not a musician. But Western music does seem to rely on the existence of a melody which build tension and then resolves it within a key. Resolution (music). (Think of the very characteristic "dut dut dut DAH" end of a piece of classical music.) So far as I am aware, certain birdsong may have harmonic, or, better, tonic characteristics. (The Blackbird song seems to.)  But as far as I am aware, only human melody has tension and resolution. Perhaps some real musician can comment. μηδείς (talk) 02:33, 25 October 2011 (UTC)
 * Your example of Beethoven's Fifth there is extremely fortuitous; our article mentions that it may have been inspired by the song of the yellowhammer. Matt Deres (talk) 13:46, 25 October 2011 (UTC)


 * Good catch, but the funny thing is I wasn't actually consciously thinking of Beethoven's Fifth, but trying to summon to mind the dramatic flourish at the end of any symphonic piece. But yeah, I did know the attribution of the theme to a bird species. I am curious if parrots will sing entire songs.  I know some do dance to them. http://www.youtube.com/watch?v=sV5bxaLDG-w μηδείς (talk) 18:27, 25 October 2011 (UTC)

Some of these might help. http://birdsinbackyards.net/feature/top-40-bird-songs.cfm(I find the grey butcher bird partcularly melodic, and this doesn't fully capture it's essence. when all the birds go crazy together in my neighbourhood at dawn, the butcher bird seems to cap it all off with the resolution Medeis mentions. HiLo48 already mentioned the magpie. There's always the Canary. I'm not a musician, so can only say what i like the sound of.. these guys might also help http://www.folkways.si.edu/albumdetails.aspx?itemid=1106 ("The Lyrebird: A Documentary Study of Its Song")WotherspoonSmith (talk) 07:34, 26 October 2011 (UTC)

kinetic theory and compression: explaining Boyle's law
It's long been intuitive -- by operating any double-action bicycle pump -- that compression of a gas beyond atmospheric pressure takes work, and that balloons undergo explosive decompression in space.... but on a kinetic level, how does the energy get transmitted? I know it's force x displacement and so forth, but suppose I am compressing a piston and I move walls ever so slightly and frictionlessly (let's say, the length of one tenth of the mean free path).

I guess I don't get the Newtonian argument that restricting the motion of a bunch of colliding particles would increase its kinetic energy -- wouldn't it have the same KE, but less freedom? I get the idea that as the walls become closer, collisions against the walls are more frequent and so the force against the walls increase.

But suppose I moved the piston so slowly that for every discrete move, I only feel the "bump" of one gas molecule at a time. In the time that I don't meet a gas molecule, force is zero, so F x d is zero. Why would moving the piston walls a little closer (cutting the mean free path of the next gas molecule short) speed up the next gas molecule? After all, if I do it slowly enough, the magnitude of momentum change should remain the same, right? elle vécut heureuse à jamais  (be free) 20:37, 24 October 2011 (UTC)
 * Kinetic theory laws and properties cannot be understood that well individually, but make much more sense in "bulk". Think about these ideas like "temperature".  An individual particle cannot have a temperature, it also cannot exert a pressure, and we cannot think of the "volume" of a gas in terms of the volume of the individual particles.  The basic properties of Kinetic Theory just don't make sense on a particle-by-particle basis.  These properties only make sense in bulk, pressure and temperature and volume require mole-level numbers of particles to start to make sense.  When you start to think of reducing the properties to the level of individual particle behaviors, the model breaks down.  -- Jayron  32  21:22, 24 October 2011 (UTC)


 * Except, my professor used a particle-by-particle approach for a "proof", and then extrapolated to all particles. While this seems to prove having a certain pressure, given n, a volume and temperature, I was trying to think of a mechanism for transmitting K.E. elle vécut heureuse  à jamais  (be free) 10:55, 25 October 2011 (UTC)


 * Actually, you can improve your though experiment by moving the wall by a small step only when there are no molecules striking the wall. So, no energy is transferred via work to the gas at all, yet we are compressing the gas. Clearly, in this case the temperature doesn't increase.


 * If you think about how you would move the piston to make sure you don't perform work, you see that you must actually move it very fast. At any moment you have molecules very close to the piston and there is always a clear space between the postion and the nearest molecule. You can then move the piston very fast to let that distance shrink a bit without hitting a single molecule. Then you wait until there is again a clear space and repreat this.


 * Then this process violates the assumption of slow quasistatic changes under with the formula for work done by the gas of p dV is valid. If you increase the volume then it is more straightforward to see that increasing the volume slowly will lead to the gas doing work. But if you suddenly increase the volume, the gas won't do any work at all.


 * In a quantum mechanics treatment you recover this result. A gas in some volume can be in states will well defined energies (so-called energy eigenstates). These are wavefunctions psi_r(x1, x2, ..., xN; V) of the coordinates x1, x2, etc. of the N molecules that depend on the volume and on a qantum mumber r that enumerates the energy levels. The energy of this state then has some value that depends on the quantum number r and on the volume, we can denote it as E_r(V). If you change the volume V very slowly, then the probability that the system will jump from one quantum number r to another becomes very small. This then means that the change in the energy if the system is given by the change in E_r(V) for fixed r.


 * If you increase the volume of the system very fast, then the wavefunction of the system will not change. This means that the the expectation value of the energy will stay the same. Count Iblis (talk) 21:54, 24 October 2011 (UTC)


 * Count Iblis's initial paragraph, describing how you wait to move the wall until there are no molecules to hit, is a varient of Maxwell's demon, which is essentially a thought experiment which shows the breakdown of the laws of thermodynamics when taken to the level of individual particles rather than bulk materials; it would provide an excellent primer on the OPs question as well. -- Jayron  32  22:18, 24 October 2011 (UTC)


 * Knowing when to move the wall would require measuring the molecules hitting it, which cannot be done without energy exchange. I guess in theory it would be possible <ith very few atoms. Given that the average free path at 1 atm is 60 nm, it's not that simple...
 * There's a 2D simulation of particles confined between a thermal reservoir and a piston at opensource physics:  Lennard-Jones PVT System http://www.opensourcephysics.org/items/detail.cfm?ID=10857 download link at bottom, java .jar file. You can move the piston and in the top right you can enter the termal conductivity of the reservoir, 0 in this case.
 * DS Belgium (talk) 01:05, 25 October 2011 (UTC)


 * I'm thinking of the case of free expansion in vacuum. No work is done, but entropy increases (irreversibly), and yet the gas must heat up if attempt to compress it back into its original volume (adiabatically). It seems I could make the gas ridiculously hot by repeating this indefinitely. So we are dealing with a sort of path function. I guess my question is, why should moving the walls transmit K.E. on a molecular scale? I know it increases K.E. from a force * distance perspective. Kinetic theory says that smaller walls means more frequent collisions -- hence higher pressure, but it doesn't seem to imply a higher temperature. [in fact we can see that a smaller volume at the same pressure implies a colder gas].   elle vécut heureuse  à jamais  (be free) 10:55, 25 October 2011 (UTC)


 * When molecules collide with moving walls they gain energy, increasing the gas temperature. Dauto (talk) 12:42, 25 October 2011 (UTC)