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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 | Contribs)} 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 - [1]. 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 | Contribs)} 01:52, 25 October 2011 (UTC)

Giant human skeleton

Are there any reliable sources for those pictures [2], [3]?--82.114.165.50 (talk) 02:00, 24 October 2011 (UTC)

No. LANTZY^TALK 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, [4], 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. -- kainaw™ 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)

---

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

→Στc. 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. -- kainaw™ 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, PMID 1622631 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 (PMID 1622631) and is "positively dependent on oral contraceptive use" (PMID 21995151). 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 ([5]) 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. (PMID 21509772 and also PMID 19569233). Another study found association of childbirth with breast cancer but not significant evidence that breastfeeding time was correlated (PMID 20851603) 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 (PMID 20521247) (I wonder how all this reconciles with a statement that abortion does not increase risk of breast cancer... PMID 21557713) 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 [6] 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. -- kainaw™ 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. -- kainaw™ 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. -- kainaw™ 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. -- kainaw™ 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). --Jayron32 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. --Jayron32 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. --Jayron32 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. --Jayron32 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)

October 25

Speed of the average water molecule at room temperature?

Can anyone give the speed in miles per hour of an average H2O molecule in a body of pure water at 1 Atmosphere and 68° Fahrenheit? The proper equation would be nice. μηδείς (talk) 02:23, 25 October 2011 (UTC)

v_ave = √ [8k_BT ÷ π ÷ m]

Plasmic Physics (talk) 02:34, 25 October 2011 (UTC)

You need to apply the equipartition theorem, because a water molecule is not a point-particle. The equipartition theorem states that the energy will be equal in all modes (on the average); so, you need to estimate the vibrational and rotational modes of energy; then count all the degrees of freedom, and divide the average total energy per molecule amongst each mode. Then, compute the velocity that corresponds to the translational motion modes. Nimur (talk) 02:42, 25 October 2011 (UTC)

Here it is: Stowe's Introduction to Statistical Mechanics and Thermodynamics. I have a hardcover red copy that I refer to as my little red book of thermal physics (they changed the cover in the 2nd edition, apparently). Stowe's textbook is essentially the only physics books you will ever need (because everything else can be derived from these principles - at least in statistical ensemble - and what else matters, besides ensemble behavior?) Unfortunately, reading this text does require at least a little preparation and familiarity with some more elementary physics and mathematics concepts. Nimur (talk) 02:53, 25 October 2011 (UTC)

Well, I would actually be happy with an approximation for ideal point particles. I just want something accurate on an order of magnitude. And I can figure out the equations with the ideal gas laws, or at least follow the derivation. But I figure there are complications for liquids, given they are not gasses. And I was hoping there must be something more obvious for water than an entire book, based on something llike pv=nRt. μηδείς (talk) 03:39, 25 October 2011 (UTC)

Okay, well here is a summary from HyperPhysics, Molecular Kinetic Energy. Unfortunately, to compute this molecular translational velocity correctly, you have to dive deep a little bit - the physics of molecular motion is nontrivial, even treated in a purely classical non-quantized way. There's no practical utility in incorrectly approximating molecular motion. Be sure you understand the difference between average speed, most probable speed, expected-value of velocity in one dimension, and so on. Ideal gases follow the Maxwellian distribution, elaborated here. Water is not an ideal gas, because it has viscosity, its molecules are asymmetric, hydrogen bonding and van der Waals forces are nonnegligible, and so on. Nimur (talk) 05:56, 25 October 2011 (UTC)

The redlink above is probably in reference to the Maxwell–Boltzmann distribution (sometimes Maxwell distribution) Grandiose (me, talk, contribs) 21:20, 25 October 2011 (UTC)

Is k_B the Boltzmann constant? Dualus (talk) 04:36, 25 October 2011 (UTC)

Yes. Plasmic Physics (talk) 04:37, 25 October 2011 (UTC)

Is there such thing as an ideal liquid, or would that just be the same thing as an ideal gas at extreme conditions? (I am wondering what would happen to the p variable.) Yes, I understand the difference between mean, median and mode. Yes, I understand that water molecules are polar, and that the angle between the hydrogen atoms varies. I can even figure out that unless a body of water is moving, the net average velocity of its particles will have to be zero. But since the atoms are indeed moving it seems reasonable to me to ask for some average speed at a given temperature and pressure. All I can remember from the gas laws is that the answer is calculable and on the order of 1000mph (or was it kph?) for air molecules, with a mean free path of ~10cm, if I remember correctly. Surely there is some sort of analog for water molecules. μηδείς (talk) 11:27, 25 October 2011 (UTC)

The assumptions of an ideal gas are dilute concentration which, a liquid is not, and very low temperatures. Plasmic Physics (talk) 11:38, 25 October 2011 (UTC)

The Van der Waals equation gives a fairly good description for a liquid while still keeping the math reasonably simple. Dauto (talk) 12:34, 25 October 2011 (UTC)

The system not being an ideal gas is irrelevant here . The translational part of the partition function factors out, so barring quantum effects, you have the Maxwell distribution for the velocity. Also that H2O is not a point particle is also irrelevant, because, again, the partition function for the translational part factors out of the configurational part rotational, vibrational parts (note that these vibrational, rotational and other internal parts may not factorize as they are coupled, but the translational part will factor out due to physics being invariant under translations).

The only issue with H2O being a liquid as far as the velocity distribution is concerned, is that there will be strong correlations between nearby molecules. Count Iblis (talk) 15:23, 25 October 2011 (UTC)

In other words, the only issue is that the actual molecular velocity depends on the non-ideal parts? I agree whole-heartedly. Except for the non-ideal parts, water is an ideal gas. The ideal velocity can ideally be calculated by ignoring any non-ideal effects. PV = nRT and such, for n spherical non-interacting water-molecules and cows. Count Iblis, while you are correct in stating that translational motion is not coupled to the rest of the molecular motion, your assertion implies that these other energy modes do not contribute to the temperature of the system: I think that assertion is incorrect.

Temperature is comprised by all the energetic degrees of freedom in a system - not just the translational kinetic energy; this is the definition of "temperature." You can't ignore the other energetic modes, especially in a molecule as complicated as the water molecule. You must define all the degrees of freedom and apply equipartition theorem. Unlike, say, Helium, these other degrees of freedom are non-negligible for water - which is why we call it a non-ideal gas (or fluid). Nimur (talk) 21:08, 25 October 2011 (UTC)

Count Iblis is right (as usual). Note that the question is not about the total energy of the molecules at a given temperature in which case you would be right and the equipartition theorem would have to be invoked. The question is about the speed of the molecules and that will be given by the Maxwell-Boltzmann distribution. Note that Count Iblis never said that the ideal gas is a good description for the liquid water. That would have been a ridiculous statement. What he said was that the Maxwell-Boltzmann distribution is a good description for the liquid water, and in that he is right. Dauto (talk) 03:38, 26 October 2011 (UTC)

Correct me if I'm wrong, but my impression from Temperature is that E_k = 1/2 kT for each degree of freedom; thus, there should never be any need to divide by the number of degrees of freedom to figure out the speed of any given particle at a given temperature. If you have a liquid made up of a mix of molecules that can stretch and rotate in a hundred different ways, and individual atoms floating free, the individual atoms don't have any way to know they're supposed to go faster than the others when they hit something (unless they have less mass, that is). Of course, those hundred different extra rotations do carry energy and are in equilibrium, so if you cool such a liquid I suppose it should release quite a bit more energy over time / larger heat capacity. Wnt (talk) 23:19, 26 October 2011 (UTC)

Lightsabers

Would plasma or lasers be better suited for a lightsaber, and which would be more practical? →Στc. 05:59, 25 October 2011 (UTC)

Neither is practical. Light sabers are impractical; they make for exciting fiction, but they defy any attempt to explain their behavior according to known physics. The real behaviors of both plasmas and lasers are very dissimilar from the special-effects that were used in Star Wars. Nimur (talk) 06:05, 25 October 2011 (UTC)

Could you explain further? →Στc. 06:14, 25 October 2011 (UTC)

Sure. Let's start with plasma. Think of a plasma as a very hot gas. It has other special properties, but your starting point for intuition should be "very hot gas." In what way do you think very hot gases behave like a sword?

Now, let's move on to a laser. Think of a laser as a very bright light. It has other special properties too, but your starting point for intuition about lasers should be "very bright light." In what way do you think very bright lights behave like a sword?

Ultimately, I'm sorry that you were exposed to fictional ideas about lasers and plasmas before you were ever exposed to nonfictional facts about them. Rest assured - both lasers and plasmas are fascinating for all sorts of reasons - but they have nothing to do with light sabers.

In fact, there are cold plasmas and dim lasers, but this doesn't change the fact that you can't build swords from either.

If you have some prior scientific knowledge, I recommend a better intuitive starting point for both concepts - albeit this requires more than laymans' terminology. A plasma is an ionized gas whose ensemble behaviors are determined by electromagnetic effects, rather than just by kinetic effects. A laser is a machine designed to amplify light, typically resulting in a very coherent, monochromatic, high power output signal. These more technical descriptions are much more accurate than the ones I gave above, but they are harder to "really" understand for a lot of people - which is why we have sci-fi stories about laser/plasma/swords. Nimur (talk) 06:43, 25 October 2011 (UTC)

The clearest way I know to explain the problems with a lightsaber in a layman's terms is to ask the following: if it is a laser, a beam of light, what caps it so it doesn't shoot off into infinity like any other beam of light, and if there is some physical cap, what holds it in place and why wouldn't a cap at the tip get caught up on things? If, on the other hand it is a plasma, what, like the glass of a neon light, holds the excited gas in place? I always figured it has to be some field-bound mono-molecular filament in some excited state. Surely there is a book on the physics of Star Wars? μηδείς (talk) 11:41, 25 October 2011 (UTC)

Better than that - there's a Wikipedia article: Physics and Star Wars. Alansplodge (talk) 12:52, 25 October 2011 (UTC)

The force bends the light. That's why you have to have the power of the force to use a light saber. Otherwise, it is just a clunky flashlight. -- kainaw™ 12:51, 25 October 2011 (UTC)

This blog has some conjecture about light sabers. Alansplodge (talk) 12:58, 25 October 2011 (UTC)

You can purchase a lightsaber in most toy shops, or you could. They are basically a translucent plastic tube with a flashlight at one end. Have fun.--Shantavira|^{feed me} 14:02, 25 October 2011 (UTC)

I wouldn't utterly rule out a kind of deliberately shaped ball lightning, but ... it's a really big stretch. Also I remember reading a news report recently (<1 month) about transmission of light in packets which somehow shape themselves, even in vacuum, to keep a bit of light in a tight bunch, but I can't find it now; you might be able to devise some handwavy explanation about how you put "english" on the original composition of such clumps of light so they boomerang back. Still, until someone turns up with a bona fide light saber it's all mist and vapors. Wnt (talk) 14:27, 25 October 2011 (UTC)

The most practical light sabers are made from computer graphics. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:35, 25 October 2011 (UTC)

How about magnets and mirrors? →Στc. 22:14, 25 October 2011 (UTC)

It is well-established that a lightsaber consists of plasma encased within a force-field. See the Wookieepedia article on lightsabers for more information. --130.216.172.199 (talk) 22:18, 25 October 2011 (UTC)

Ok, but since "force-fields" are complete make-believe that just brings us back to where we started. APL (talk) 03:02, 26 October 2011 (UTC)

Oh, well that's reassuring. Since the plasma is kept safely contained within a force field, you can't accidentally cut your fingers on it ... ? Wnt (talk) 23:06, 26 October 2011 (UTC)

Watch the following video series, http://www.youtube.com/watch?v=xSNubaa7n9o This is about as close as you will get to a working lightsaber, but obviously there are more practical uses of the technology used in Michio Kaku's design. ScienceApe (talk) 15:43, 26 October 2011 (UTC)

Hello chaps - digging way back into the Lightsaber article history gives us this choice info :-

"Lightsabers, made of immaterial beams of light, collide when they should pass right through one another without a sound. Moreover, laser beams propagate in a straight line as long as they do not meet an obstacle, therefore scientifically correct lightsaber blades would cut through a starship hull. This would mean that dueling with lightsabers would be like dueling with flashlights because the blades would pass through each other and continue to travel until they hit an object, not reflecting back onto themselves.

Instead of a laser-based device, the most believable design for a lightsaber-like device would use plasma confined by a magnetic field. Plasma is a super-heated gas and is also the fourth state of matter, the color and luminosity of which varies depending on the temperature and composition. Plasma could be ionized by a particle beam from a compact particle accelerator; at relativistic energies, the beam would produce its own blue glow along its axis from Cherenkov radiation.

Keeping a gas in the plasma-state requires considerable energy: 40 kW are necessary for a 10 centimeter (4 in) saber at 10,000°C (18,000°F). It would be difficult to fit the required generator into the saber's hilt. To control and increase the length of the blade, the plasma would need to be confined within a magnetic field. Although this design would behave like a lightsaber from the Star Wars movies, it is considered foolhardy to confine plasma magnetically. A handful of magnets would disrupt the confinement field, and plasma would spill onto the saber's wielder. Furthermore, the magnetic field would prevent the plasma from performing any cutting action because it would always be shielded from whatever the blade struck by the magnetic field.

To make a semi-solid beam of energy which could interact with both matter and energy would require containing a quasar and quantum singularity inside the hilt. The gravitational field would pull all the quasar's expelled plasma back moments after the quasar releases them. The speed of the returning plasma would form a chainsaw effect allowing it to cut through the matter with ease, while still being stopped by an opposing beam. A modulated gravity field would bounce, allowing for the reflection of energy beams. So far, no known substance exists which is able to contain a quantum singularity or to contain and/or focus a gravitational field.

A lightsaber in reality would be difficult to wield, since its center of gravity would be in the hilt next to the hand. A real sword has its center of gravity further from the hand, which allows the user more control and power in the swings and thrusts. With a lightsaber, a user would need to have much more control and wrist strength in order to accurately use a lightsaber with strength and power. However, because the blade is supposed to be made of light, it would have no weight at all. In that instance, the blade would move easily while the hilt moved slowly. According to commentaries on the prequel trilogy DVDs, the lightsaber props were indeed built so that their center of gravity was centered in the hilt, as if there was no blade at all."

Quintessential British Gentleman (talk) 19:56, 26 October 2011 (UTC)

" Furthermore, the magnetic field would prevent the plasma from performing any cutting action because it would always be shielded from whatever the blade struck by the magnetic field." -- Only if the "whatever the blade struck" was magnetic in its own right. 67.169.177.176 (talk) 06:01, 27 October 2011 (UTC)

I see Luke Skywalker pulling and pushing and kicking and hammering and cursing at a light saber stuck firmly to (or in...) the deck of the Millennium Falcon, while the ghost of Yoda softly whispers, "Use the force, Luke!" Wnt (talk) 17:48, 27 October 2011 (UTC)

Just watched an interesting program where in they will use a new type of plasma engine; basically the plasma is accelerated out the back of the engine using magnets that are kept at extremely cold temps and only acts as magnets when cold, so if you can now effect the shape of plasma and the speed it comes out of on a miniature scale say ""hand held"" scale then a very hot jet of plasma being brought across the enemy from a hand held device would certainly give you a bad day and would equate some what to a weapon or Sword...

... the drawback, of course, being that the radiant heat from this "plasma sword" would give the person wielding it flashburns as well. (BTW, why don't you sign your posts w/ four ~'s?) 67.169.177.176 (talk) 23:48, 29 October 2011 (UTC)

" dissolving " water in other solvents

How can I calculate the amount of water I can " dissolve " into another solvent. For instance how can I calculate the amount of water that can dissolve in octanol before one can percieve two different phases? — Preceding unsigned comment added by 137.224.252.10 (talk) 09:48, 25 October 2011 (UTC)

You can't, you have to find it through experimentation. Plasmic Physics (talk) 12:33, 25 October 2011 (UTC)

Are there tables where you can look up this kind of thing? — Preceding unsigned comment added by 137.224.252.10 (talk) 12:48, 25 October 2011 (UTC)

See solubility chart and solubility table. μηδείς (talk) 17:42, 25 October 2011 (UTC)

Octanol doesn't mix well with water, so you'll only be able to dissolve a small amount of water in it before you get phase separation. (Best way to find out how small is to actually try it.) 67.169.177.176 (talk) 01:29, 26 October 2011 (UTC)

Just checked the solubility chart: the solubility product is negligible, so you might not be able to dissolve any water in octanol at all. 67.169.177.176 (talk) 01:32, 26 October 2011 (UTC)

Are you sure you looked under octanol, and not octane? "At 25 °C, the solubility of water in octanol is quite large, approximately 0.275 mole fraction, but the solubility of octanol in water is just 7.5 × 10 −5 mole fraction." [[7]]. See the Ropel reference. Dominus Vobisdu (talk) 02:07, 26 October 2011 (UTC)

Yes, I checked under octanol, C₈H₁₇OH. However, it does appear to me that I was looking at the octanol-in-water number rather than water-in-octanol. I stand corrected. 67.169.177.176 (talk) 02:47, 26 October 2011 (UTC)

Everything disolves, a concentration measureable in nanomoles or picomoles per cubic decimentre is still a concentration. Plasmic Physics (talk) 01:42, 26 October 2011 (UTC)

Thanks to everyone for their replies. They have been very helpful! — Preceding unsigned comment added by 137.224.252.10 (talk) 11:12, 26 October 2011 (UTC)

Price of airplane ticket: weight vs. volume

First or business class tickets are much more expensive than tourist class. However, you weigh the same, no matter what class you fly, but occupy more space, depending of class. Does that means that for airplanes, the volume you occupy if more important for determining the cost than your weight? Or is it simply a market dynamic: they charge more because they can. Strangely, when you send a package they normally charge you by weight. Quest09 (talk) 13:20, 25 October 2011 (UTC)

Well, skimming the article, a Boeing 747 has a maximum takeoff weight of 735,000 to 970,000 pounds, and seats up to 550 passengers. (There are all kinds of variations painstakingly documented there, which I basically ignored; a more careful reading may get you more accurate figures) At anywhere from 1330 to 1760 pounds per passenger, the passenger weight is a pretty small factor. Wnt (talk) 14:17, 25 October 2011 (UTC)

Don't forget fuel weight, it makes a huge difference. Our 747 article doesn't contain enough info for a proper calculation, but for the Boeing 727 one can work out that fully loaded and fully fueled, there is capacity for somewhere in the neighborhood of 250 pounds per passenger, including luggage. Looie496 (talk) 20:17, 25 October 2011 (UTC)

Well, I suppose that's how they define "fully" fueled. But jetliners don't usually fly with full fuel. Wnt (talk) 16:49, 26 October 2011 (UTC)

Also, the US postal service has recently been ggressively advertising a Flat Rate Priority Mail program with presized boxes and a slogan "if it fits it ships", so I think this applies to some extent to air shipping also. Wnt (talk) 14:19, 25 October 2011 (UTC)

The smallest USPS Flat Rate envelope comes with a 70lb domestic and 4lb international weight limit.μηδείς (talk) 16:00, 25 October 2011 (UTC)

Drat, I thought I had found a cheaper way to mail plutonium to people I dislike. :-) StuRat (talk) 03:04, 26 October 2011 (UTC)

The cost of flying a plane from A to B is basically fixed. You then want to maximise the amount of money you make from the flight. That's determined by business concerns, not engineering ones. First class doesn't really exist to make money by being sold. I don't have any figures, but I don't believe many first class tickets are sold. The seats are often either empty or filled with people that got upgrades (either free or with airmiles). They exist to serve as a reward for their frequent flier programs (which exist to get people to buy more economy and business tickets), and also to make business class look cheap by comparison. The improvements from business to first are minimal, at least in the air (you do get some special treatment on the ground with a lot of airlines), so very few people would pay the enormous increase in price just to get them. You travel first class either because it's a free/airmiles upgrade, someone else is paying, or you want to do so for the sake of it (eg. to show off how rich you are, or because it makes your honeymoon more special). Once you are rich enough for the extra price not to be significant to you, you're probably chartering private jets rather than travelling on commercial flights. Business class is a significant improvement on economy, so is worth the money to a lot of people - I'm not sure airlines actually make more from a business class seat than they would by filling the same space with economy seats, but they would struggle to get businesses to name them are their preferred airline if they didn't offer it, even if the business usually flies people economy. (Apologies for the complete lack of references - I'll try and find some later and will come back!) --Tango (talk) 18:17, 25 October 2011 (UTC)

Minor comment: the cost of operating an aircraft does vary as a result of fuel consumption; and fuel efficiency does vary as a result of gross takeoff weight; so it's not a totally fixed cost to fly a plane from A to B. Otherwise, Tango's pretty spot-on; most of the short-term decisions in commercial aviation are made on the basis of marketing and business choices, not on engineering limitations of the aircraft. Over the much longer term, major airlines choose how to strategically invest in their fleets in order to keep their operations in line with their business objectives: for example, purchasing large aircraft versus small aircraft; regional- vs. transcontinental- aircraft; and so on. Southwest Airlines is often cited for operating an all-737 fleet - excellent, versatile, large aircraft. (No first-class on SouthWest, either). This consolidates planning, maintenance, training, and other costs, but also consolidates risk. Two business analyses, both from Forbes: Southwest Gives Fleet A Facelift, And Saves Some Dough Too; and following a 737-related aircraft safety incident, Southwest shares drop.... Corporate strategy is a finely-tuned game of highly-quantitative guess-work. Nimur (talk) 19:20, 25 October 2011 (UTC)

Boas vs. pythons

After reading this summary of the similarities and differences between boas and pythons, I had the following insight: without the anatomic and physiologic distinctions between the two families, the matter of inhabiting different locations would be irrelevant. Is difference in worldly habitat really, then, a difference between the two families? As a contrast, I offer the distinction between polar bears and giant pandas, which not only possess anatomic and physiologic differences, but a uniqueness in their areas of distribution that is, I think, somewhat necessary to their survival -- pandas could not exist in the arctic circle, although polar bears could probably live in China, as they do in zoos all over the world. DRosenbach ^{(Talk | Contribs)} 13:36, 25 October 2011 (UTC)

Well, I think you're missing a key concept here: There is a relationship, an interrelatedness between the environment an organism lives in and the particular physiological and genetic traits that produce them. Two important things: 1) None of the three factors is absolutely responsible: organisms change their environment, environmental pressures cause genetic changes, genetic changes cause changes in form and behavior, which cause further environmental changes. It is a series of complex feedbacks all affecting each other. 2) Nothing is static. The system of relationships changes continuously and never settles into any static set of relationships. There are periods of precarious equilibrium where some locations and some times show periods of stability, but nothing is ever permanent. --Jayron32 15:25, 25 October 2011 (UTC)

Your points are well taken, Jayron32, but my question revolves around the notion that, despite the loosely-fitting old-world/new-world classification of pythons and boas, respectively, introducing boas into Australia or Africa or pythons into Central America (or South Florida) doesn't seem to affect the species, unlike moving a panda into the arctic. If a difference is that boas don't naturally inhabit Australia and pythons don't naturally inhabit, but that difference is really only consequential as a side point (as can be demonstrated by invasive species of feral pythons in S. FL) -- is it really accurate to refer to it as a difference? DRosenbach ^{(Talk | Contribs)} 16:40, 25 October 2011 (UTC)

The fact that a species can survive in a place doesn't mean it isn't different from the species native to a place; invasive species can thrive and actually greatly alter an environment; it doesn't mean that they are somehow indistinct from native species. C.f. rabits in Austrialia. --Jayron32 20:38, 25 October 2011 (UTC)

Modern taxonomy uses cladistics which groups species by their evolutionary history. One cause of populations drifting apart evolutionarily into separate species is that two groups become geographically separated so they no longer interbreed. The differences in the geographic ranges of two families can say a lot about evolutionary distance. Rckrone (talk) 03:54, 26 October 2011 (UTC)

EMP effects on artificial pacemakers

What would be the effects of an exposure to EMP from a short distance on artificial pacemakers (will they stop working? for a limited period of time? permanently? and why?), and the person who owns it? (please correct my English)

It is difficult to find precise information, but the general conclusion seems to be that artificial pacemakers are susceptible to damage from a sufficiently strong EMP. Looie496 (talk) 18:04, 25 October 2011 (UTC)

I'd think it would have to be a very strong and/or close EMP, since the main susceptibility to EMP is due to long wires which build up charge over miles (such as electrical transmission wires on high tension towers). The wires on a pacemaker are relatively short. StuRat (talk) 03:09, 26 October 2011 (UTC)

...and the voltage required to screw it up is relatively small. SpinningSpark 21:46, 26 October 2011 (UTC)

Decapitation

Could any of you give me a brief description of what ligaments, muscles and bones would be cut through by a killer using an axe to sever a human head please? — Preceding unsigned comment added by IsonomicJedi (talk • contribs) 16:37, 25 October 2011 (UTC)

You can check google images for an "axial section of the neck," but this diagram looks like it answers your question. If you include the term 'Netter' (he's a very famous and accomplished anatomy illustrator) you'll likely get better results. DRosenbach ^{(Talk | Contribs)} 16:43, 25 October 2011 (UTC)

Note though that using an ordinary axe to sever a human head is essentially impossible. Even professional executioners, tremendously strong and well-trained and using a much broader and much sharper axe on a victim lying stretched out motionless in front of them, frequently failed on the first try. With an ordinary axe all the killer would do it make a gory mess. Looie496 (talk) 17:55, 25 October 2011 (UTC)

Hence the guillotine, leading edge technology of its day. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:28, 25 October 2011 (UTC)

Cutting edge technology, surely? Greglocock (talk) 00:28, 26 October 2011 (UTC)

Or bleeding edge technology, perhaps ? StuRat (talk) 03:17, 26 October 2011 (UTC)

D'oh! I missed that obvious punning situation. And don't call me... you know. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:02, 26 October 2011 (UTC)

...sharp? Pfly (talk) 03:26, 27 October 2011 (UTC)

Did you have to be so blunt? Nil Einne (talk) 09:34, 27 October 2011 (UTC)

Earthquakes and Brick Buildings

In terms of safety, would brick buildings be a good choice in an earthquakeprone area? Compared to, for example, timber construction or steel frame buildings. Thanks, Wanderer57 (talk) 18:20, 25 October 2011 (UTC)

Brick buildings are the absolute worst. In earthquake-prone parts of California they are forbidden. Steel is best, timber next. Concrete is bad, brick just disintegrates. Looie496 (talk) 18:34, 25 October 2011 (UTC)

Around these parts of California, you hear the terminology "un-reinforced masonry construction" - it's not merely that the bricks are present, its that structural integrity of the building is entirely dependent on the "glue" (the mason's mortar) that holds each brick together. An unreinforced brick building will "disintegrate," if the shaking gets bad enough. If the building had rebar steel inside it, and brick on the outside, the problem is less severe: the building may remain standing in an earthquake even if the mortar cracks and disintegrates, and bricks fall off. However, you still have the serious problem of falling bricks coming off the side walls: this can be very hazardous. Even if the building doesn't collapse, it only takes one loosened brick falling from just a few feet up on a wall to land on your head, causing a serious casualty or fatality. (I used to think - how unlikely is that? What's the probability of one brick falling and landing on your head? ... But after surviving a few earthquakes, I realized ... the entire region is shaking - somewhere in a fifty mile radius, somebody is standing near a brick wall that could will collapse). It's safer to avoid such construction altogether. Here's more information from the State of California: Typical Unreinforced Masonry Building Damage from our multi-county regional planning commission in the San Francisco Bay area; and here's Putting Down Roots in Earthquake Country from the Federal Government (the USGS). Lots of good photos and statistical information in that one; you can order a free paper-copy from the US Geological Survey if you want one. Nimur (talk) 19:05, 25 October 2011 (UTC)

Generally there are requirements to retrofit such buildings in earthquake-prone areas by putting in cross-braces, so that there is something that actually holds the building together should a quake occur. Mikenorton (talk) 19:20, 25 October 2011 (UTC)

Instead of bricks, if you use cinder blocks, and run rebar through the hole in each, you can come up with a reasonably safe construction. StuRat (talk) 03:15, 26 October 2011 (UTC)

Wood frame construction is surprisingly durable in an earthquake, provided it's tied to its foundation properly. As noted above, unreinforced masonry performs poorly: it can just come apart. While it's possible to engineer such structures to withstand earthquakes, that work involves inserting what amounts to a parallel structure into the masonry building to deal with the forces that masonry can't withstand. Examples of unreinforced masonry include the Washington Monument and Washington National Cathedral, which suffered significant damage in a rather moderate earthquake. Acroterion (talk) 17:16, 26 October 2011 (UTC)

Thank you all. My question was prompted by the situation of Bangladesh. I'm led to believe that Bangladesh is in an active seismic area, is substantially a delta susceptible to shaking, and uses bricks as a major construction material because the soil can easily be used to make bricks. Comments? Wanderer57 (talk) 05:05, 27 October 2011 (UTC)

It lies close to the plate boundary between the Indian Plate and the Eurasian Plate and the earthquake hazard will increase in the northern and eastern parts of the country where the boundary lies, although it is significant everywhere. This suggests that the country is relatively unprepared for a major earthquake, such as the 1897 Assam earthquake, which severely affected the area that is now Bangladesh, with most of the brick buildings in Dhaka being destroyed (according to this). Mikenorton (talk) 07:22, 27 October 2011 (UTC)

You can also have a look at the Modified Mercalli scale for earthquake damage to various types of masonry. Soft soils are especially prone to soil liquefaction. ~AH1 ^(discuss!) 20:28, 29 October 2011 (UTC)

October 26

Phase space

How to calculate number of quantumstaes or unit cells within energy range E and E+dE in the phase space to prove the eqn: g(E)dE=[(8π√2V)/h^3]*m^(3/2)√EdE — Preceding unsigned comment added by Intr199 (talk • contribs) 13:41, 26 October 2011 (UTC)

The number of states in a volume d^3p of momentum space is

V/h^3 d^3p

You can write this in terms of dE by integrating over all angles. This leaves you with:

V/h^3 4 pi p^2 d|p| = V/h^3 4/3 pi d|p|^3 =

(using E = p^2/(2m))

V/h^3 4/3 pi d (2 m E)^(3/2) =

V/h^3 4/3 pi (2m)^(3/2) 3/2 E^(1/2) dE =

V/h^3 4 sqrt(2) pi m^(3/2) E^(1/2) dE

If the particles have spin 1/2, then you need to multiply this by 2. Count Iblis (talk) 15:34, 26 October 2011 (UTC)

"using E = p^2/(2m)"

why kinetic energy is being considered only?Intr199 (talk) 16:40, 26 October 2011 (UTC)

This is for free particles. There is actually a potential, the particle is confined to a volume, so you can consider the case of a particle in a box, solve the Schrödinger equation and then derive this result. Count Iblis (talk) 23:22, 26 October 2011 (UTC)

Can just anybody get fat?

I'm not sure how to search for this, so I'll just throw out as a question and see what I get: can a great majority of average men of normal height reach BMI of 45/body weight of 150 kg or so (330 pounds) simply by eating a lot, if they tried? Or would many of them develop type II diabetes and just pee out the sugar or otherwise run into obstacles preventing the attempt? (I'm not interested in psychological/social factors here, only the metabolism) Wnt (talk) 17:28, 26 October 2011 (UTC)

Sure, when energy input exceeds energy used you gain weight. It's a simple equation. You can also get type II diabetes. It isn't like an either/or proposition. --Jayron32 17:43, 26 October 2011 (UTC)

There are a few people whose metabolism doesn't allow them to get fat, whatever they eat. This seems particularly true during growth spurts in the teenage years, and for those who are athletic. However, the majority of people seem to pack on pounds quite easily. The only question, then, is if they could reach that weight without dying first. Diabetes doesn't keep you from gaining further weight, but it could kill you. However, due to modern medicine, insulin should keep them alive until they reach the weight you want. (Planning a cannibal feast ?) StuRat (talk) 17:55, 26 October 2011 (UTC)

I know some people can get a lot of junk and don't seem to get fat. This doesn't mean they have a metabolism that doesn't allow them to get fat. It's possible if they really tried, e.g. if someone forced them to eat 10 Big Mac combos and a 10 pack of KFC a day, they would get fat. They may vomit or have other problems at first but it wouldn't surprise me if they would eventually learn to adapt. Nil Einne (talk) 18:22, 26 October 2011 (UTC)

StuRat: I'm wondering if there is any real difference between a highly obese person with type II diabetes, and a normal person with no propensity to become overweight, except for the obesity. It seems like what would be called insufficient insulin production from the pancreas for an obese person would still be enough to provide for all the cells of a person of normal weight; likewise the insulin resistance would likely be much reduced or eliminated for such a person at normal weight. If that is true, then in overweight people, is type II diabetes a disease at all, or merely a symptom of obesity? To take this reasoning to the furthest extreme, what if hyperinsulinism is the real disease, leading to the excessive weight gain (as suggested by places like [8]) - is it possible that the subsequent onset of type II diabetes in obese people actually represents the remission of the condition of excess insulin production, so that it is then possible to lose weight more readily and avoid all adverse health effects? Wnt (talk) 19:50, 26 October 2011 (UTC)

You might be interested in a documentary called "Why Thin People are not Fat. I believe it is available online for free. From memory they said it was largely genetic and it's not easy to get some people to put on weight, even when they're trying to force it. Vespine (talk) 21:16, 26 October 2011 (UTC)

I saw that documentary, but I think that most people would fall in that category if they only made sure they were physically very fit well before they reached adulthood and stayed that way. The real problem is that the Western way of living has been made the standard for healthy living, while it is actually the cause of problems. Things are slowly changing, it has recently been realized that walking alone is not good exercise (unless you are past 75 years of age), you really need to exercise intensely, (at a heart rate of 140 bpm or higher). Count Iblis (talk) 23:37, 26 October 2011 (UTC)

To pick up on one point above, I read over and over again that a modest amount of walking IS good exercise. Is giving this advice an act of desperation to try to encourage ANY level of activity? Wanderer57 (talk) 04:28, 27 October 2011 (UTC)

Hmmm. I have need of such information myself, so searching exercise "beats per minute" on PubMed and just dumping the results in reverse chronological order: PMID 19501315 prescribes 110 to 130 bpm for pregnant and perhaps postpartum women for up to 150 minutes/week of aerobic activity. [9] tests an exercise regimen for "beneficial autonomic effects on the heart" using a formula of 70% * (220 (+6 if female) - age) bpm; however no evidence is given that this remarkable formula is better than others. Another study [10] also uses this and shows results on cardiovascular scores. [11] showed that exercise reaching a peak of >150 bpm reduced snoring in obese children, with 40 minutes being roughly twice as effective as 20 minutes. Osteogenic index and ground reaction force improve when exercise is over 135 bpm ( PMID 16920771 ) ... if only I understood what that means. Now [12] starts to get down to brass tacks in their discussion - apparently there is a problem, chronotropic incompetence, where people fail to reach the expected bpm in a treadmill exercise test (which I assume is equal exercise for anyone doing it) - in a test group of heart failure patients they came out 10 bpm slower than the others; then they take longer to return to normal heart rate afterward. This illustrates a potential problem with studies of the effect of 140 bpm exercise, because people who can't reach 140 bpm will be excluded from the group, reducing the observed mortality in that group. Prescribing a set 20 bpm increase in heart rate is unsatisfactory in cardiac rehabilitation in terms of the total oxygen reserve. (PMID 15235299) Exercise at 163 bpm but not 132 bpm in women caused a decrease in body fat and a decrease in the intake of saturated fat and cholesterol in a test group of women (PMID 9013436). Both aerobic exercise and weight training caused decrease vascular resistance in the forearm (PMID 9004105). Exercise at 120 bpm improved glucose readings and C-peptide levels in type II diabetics (PMID 8911982). "50-70% maximal effort" reduces abdominal fat and improves cardiovascular risk factors in type II diabetics (PMID 8582541 - also PMID 2019225 for 60-80%). VO2max can be improved by 166 bpm exercise in children (PMID 7567326 - also PMID 2007150 for 151 bpm in obese children). Jogging at 70-75% of maximal heart rate in coronary heart patients increased muscle and decreased fat by about a pound (PMID 666558).

Looking at all this, what I'm seeing is that a) there are many different criteria for whether exercise "works", depending on the health and what you're using it for; b) there is an overreliance on witchy formulas that equate years of age with bpms, which reminds me of the now-discredited "120+age" formula for high blood pressure; c) frustratingly, while studies use all different standards of exercise, nobody wants to compare X bpm with Y bpm and see how effective they are toward a specific measurement. The result is a situation where it looks like the individual pretty much has to try and see for himself, or rely on anecdotal evidence from internet forums. I'm rather disappointed by the low quality and disorganization of scientific study of what is probably the leading health issue of this era. Wnt (talk) 16:38, 27 October 2011 (UTC)

Photon to electron

Can a photon be converted into an electron, neutron or proton?--195.94.11.17 (talk) 18:30, 26 October 2011 (UTC)

Sort of. There are certain conditions where a photon may spontaneously produce an positron-electron pair, see Pair production. Pair production is used in the explanation of Hawking radiation and Pair-instability supernova. As far as my limited understanding of particle physics tells me, it wouldn't work with neutrons or protons because those are composite particles, not fundemental particles. That is, protons and neutrons are themselves composed of smaller particles, called quarks. Electrons, however, are fundemental particles, and may be produced as via pair production, as may other fundemental particles. --Jayron32 19:05, 26 October 2011 (UTC)

Composite particles can be pair-produced. There's very little difference between composite and fundamental particles in particle physics. It has been proposed many times that the Standard Model fundamental particles are actually composite, and it was even proposed that there's no such thing as a fundamental particle (bootstrap model). -- BenRG (talk) 01:52, 27 October 2011 (UTC)

So it's turtles all the way down then? --Jayron32 01:56, 27 October 2011 (UTC)

Apparently yes. Turtles on top of turtles, even unto the Nth generation. I wonder if that is occasion for encouragement or despair. Wanderer57 (talk) 05:11, 27 October 2011 (UTC)

Maybe I should have made it clearer that the bootstrap model was a failure, and the successful Standard Model does have elementary particles. You can never be absolutely sure that they're not composite, because it's hard to tell the difference (the fact that electrons can be pair-produced doesn't help, for example). But the increasingly precise experimental confirmations of the Standard Model do make it increasingly implausible that they're composite. -- BenRG (talk) 20:27, 27 October 2011 (UTC)

There are certain rules that must be followed when considering whether a group of particles can transform in a different group. Those rules include conservation of energy, conservation of momentum, angular momentum, conservation of electric charge, and so forth and so on (There are too many for me to list them all here). Because of all that, a single photon by itself cannot transform into anything else. There just isn't any way to avoid breaking all the rules, so it doesn't happen. But if the photon collides with something else, allowing it to shed some excess energy, then pair production as described by Jayron in the previous post can happen. Dauto (talk) 20:03, 26 October 2011 (UTC)

Dry ice snow

According to our article on Vostok Station, the coldest naturally occuring temperature recorded on earth is -89.2°C. This is colder than the freezing point of carbon dioxide. Has dry ice snow ever actually been observed? SpinningSpark 21:32, 26 October 2011 (UTC)

This has been asked before -- the answer is no; here is a thorough explanation of why (basically, because the freezing point is pressure-dependent). Looie496 (talk) 21:44, 26 October 2011 (UTC)

I asked myself the same question a few years back. I came to the conclusion that CO2 snow was unlikely -as it requires colder temperatures to form. I thought it possible, that liquid CO2 might form on the floors of basement/cellars were it would natural collect (colder temperatures would make it sink to these places). However, I never found any accounts that this had been observed, only that people reported 'coughing' due to the high levels of CO2 when descending down into them.--Aspro (talk) 21:55, 26 October 2011 (UTC)

CO2 doesn't become liquid at sea-level pressure. You need at least five times more pressure to produce liquid CO2. That's why dry ice is dry. Dauto (talk) 22:05, 26 October 2011 (UTC)

(EC)Just because the temperature is below the freezing point doesn't mean the CO2 will freeze. A more familiar situation might help you understand. Right now where you are the air temperature is below the 100 Celsius boiling point of water but that doesn't mean that the water vapor in the air will start condensing. In fact, the opposite is more likely to happen and if you spill some water on the table it will evaporate over time. That happens because the air is not saturate with water vapor - that is the water vapor partial pressure is below the saturation partial pressure. The CO2 partial pressure in our atmosphere is just to small to get even close to saturation (even at Vostock). Dauto (talk) 22:02, 26 October 2011 (UTC)

Is that quite the same thing? I mean, clouds form and rain happens (just rarely indoors).  Card Zero  (talk) 17:01, 27 October 2011 (UTC)

Clouds form when relative humidity reaches 100% - that is when the air is saturated. Dauto (talk) 23:22, 27 October 2011 (UTC)

October 27

At the time of when Islam was first arose...

Did we know of any other planets in the solar system? ScienceApe (talk) 02:55, 27 October 2011 (UTC)

That would depend on who you talked to. Nevard (talk) 03:17, 27 October 2011 (UTC)

The existence of five other planets has been known since at least ancient times, if not prehistoric, by pretty much everyone everywhere--at the very least Venus, Mars, Jupiter, and, I would think, Saturn. Mercury might have been harder to notice by prehistoric peoples everywhere, I'm not sure. I have never knowingly seen Mercury, but then I've always lived with urban light pollution. Anyway, see History of astronomy, Venus#Historic understanding, Mars#Historical observations, Jupiter#Ancient mythology, Saturn#Ancient observations, and Mercury (planet)#Ancient astronomers. Islam first arose in the early 600s AD, of course. What prehistoric and ancient people thought these planets were and why they moved through the sky the way they did is a different question. Pfly (talk) 04:11, 27 October 2011 (UTC)

It should probably be mentioned here that the dawn of Islamic astronomy marked a real advance on earlier knowledge - an emphasis on empirical observation had long-lasting effects on the development of astronomy as a science. One should note that even today, many of the visible stars have names of Arabic origin: e.g. Aldebran, Deneb, Rigel, and all the other stars found in our List of Arabic star names. AndyTheGrump (talk) 04:25, 27 October 2011 (UTC)

See classical planet - the Babylonians knew the planets and called them by sort of the same meanings under different names (i.e. Ishtar was Venus, Marduk was Jupiter, Nabu was Mercury, Nergal was Mars, Ninib was Saturn. I don't know how many of the correspondences in the roles of the deities with those of the Romans were invented or exaggerated after the fact by commentators. Wnt (talk) 16:47, 27 October 2011 (UTC)

If a proton were the size of our sun...

How big would an electron be approximately? And if it were just one electron, about how far out would its probability cloud be if the proton were where the sun is? Just to be clear I'm aware that the bohr model isn't accurate. ScienceApe (talk) 02:58, 27 October 2011 (UTC)

An electron is a point particle, so it's unclear what is meant by the phrase "how big would an electron be". However, I can give an idea of some of the relative sizes involved. Expressing everything in the same units (picometers) for easier comparison, in increasing size, the charge radius of a proton is about 0.000877 pm, the classical electron radius (which isn't really the radius of an electron) is about 0.00282 pm, the Compton wavelength of an electron is 2.4 pm, and the Bohr radius is 53 pm. Multiplying those four numbers by the same constant gives 1 solar radius, 3.2 solar radii, 2,700 solar radii, and 60,000 solar radii, respectively. In comparison, 1 astronomical unit is about 215 solar radii, so divide those four numbers by 215 if you'd prefer to measure everything in AU instead of solar radii. Red Act (talk) 07:12, 27 October 2011 (UTC)

The proton article gives a proton radius of 1.6 to 1.7 femtometers. The Bohr radius is 53 picometers. So we'd put the electron at 32000 solar diameters out. The solar diameter is 1392000 km, so that's 44 700 000 000 km = 299 astronomical units. Which oddly enough is close to Red Act's 280 despite the apparent difference in derivation. Wnt (talk) 17:01, 27 October 2011 (UTC)

There's nothing particularly odd about it. The proton article gives the proton's diameter as 1.6-1.7 femtometers, which is roughly consistent with the 0.000877 picometer charge radius that I used, which is why our answers are roughly consistent. Despite your misspeaking above, you did actually use the 1.6-1.7 femtometers as a diameter in your calculation, not a radius, so that didn't create a discrepancy between our answers. Red Act (talk) 17:50, 27 October 2011 (UTC)

Rods and cones in the male/female eye

I've noticed that my brother and I can usually see quite well in the dark, whereas many women I know have to strain their eyes to see things at night (like mountains) that I can see easily. This set me wondering, do females have less cones than males? If so, do they have more rods? And are the effects of this noticeable? Can females differentiate between colours better than males? Thanks, --T H F S W (T · C · E) 03:00, 27 October 2011 (UTC)

I'm not sure all of the specifics, but one key difference is that males are 16 times more likely to be colorblind than females, see Color_blindness#Genetics. My understanding is that a lot of color perception genetic coding is on the X-chromosome and consists mostly of dominant genes. In females, with two X-chromosomes, the presense of the recessive "color blindness" gene can be masked by the dominant gene on the second X chromosome. Males, with only one X-chromosome, don't have that second gene, so if they have the color blindness gene, it always manifests itself. I'm not sure what this means for general (non-defective) vision differences between males and females, but there may be something there. --Jayron32 03:42, 27 October 2011 (UTC)

You appear to be stating your question backwards of how you're intending it. Rod cells are the ones responsible for night vision, and cone cells are responsible for color vision.

Number of rod cells would be only one potential difference that might affect night vision.

This study, at least, would seem to suggest that women might if anything tend to have better low-luminance visual acuity than men. Red Act (talk) 04:57, 27 October 2011 (UTC)

I think this would be a hard comparison to make, because it takes a long time for night vision to reach maximum sensitivity. You would have to be sure that you were comparing males and females who had both been in the dark for equally long. Looie496 (talk) 05:00, 27 October 2011 (UTC)

Night vision may depend on eye colour. I believe I have read that people with blue eyes have better night vision than those with brown eyes. Some women are tetrachromatic, and do have superior colour discrimination.--Srleffler (talk) 17:20, 27 October 2011 (UTC)

(edit conflict) Sorry, got the rods and cones mixed up in my original question. I read the study, but since the youngest participant was 56 I think the results could have been because females' eye's don't go bad as fast as males' or something similar. And when I noticed this both the males and females had been in the dark for the same amount of time. --T H F S W (T · C · E) 17:25, 27 October 2011 (UTC)

I would expect women to have better colour discrimination since I'm guessing they have more cones and less rods. But I'm wondering is if having better night vision probably means having worse colour discrimination, and vice versa. --T H F S W (T · C · E) 17:27, 27 October 2011 (UTC)

Color vision also depends on the way you were raised, the language you speak etc. Count Iblis (talk) 00:09, 28 October 2011 (UTC)

I looked for published papers about Himba color perception and found this one, which is linked from the Himba people article. Those researchers found that their Himba subjects' ability to recall colors was correlated with their color vocabulary (not just the basic color terms of the language they spoke, but each individual subject's vocabulary). I don't find that very surprising. If you're shown a color and later asked to pick it out of a lineup, you're more likely to succeed if you habitually use words like "magenta" and "violet". But if you're asked to match a color against a set of others, all presented together, your success rate isn't going to be any higher than someone who calls them all "purple", assuming you both have normal color vision.

The phenomenon shown in that BBC documentary, on the other hand, would be extraordinary and revolutionary if true, not to mention apparently at odds with the results of Roberson et al (all of whose subjects tested normal for color vision). Yet I didn't find a single paper about it. Serge Caparos seems to be a real researcher who has worked with the Himba, but his research seems to have nothing to do with color perception. That section of the "Himba people" article is marked [citation needed]. If you can find a published description of the experimental procedure and results, I'll read it. Otherwise I'm going to chalk this up to creative editing on the filmmakers' part. The Great Eskimo Vocabulary Hoax is a good read. -- BenRG (talk) 04:56, 28 October 2011 (UTC)

Laws of Physics

Is there any law of advanced physics that says that a body may travel from point A to B without actually having to cross the actual distance between these two points ( or any other possible path )?  Jon Ascton  (talk) 04:30, 27 October 2011 (UTC)

There are several features of quantum mechanics that pertain to your question. For one thing, at extremely small scales, objects don't really take any specific path from A to B, so much as take all possible paths from A to B; see Double-slit experiment. Also, objects can go from A to B by going through a region where the object would classically be prohibited from going due to energy considerations; see Quantum tunneling. Also, a qubit can be transmitted from A to B, without being transmitted through the intervening space; see Quantum teleportation. Red Act (talk) 05:24, 27 October 2011 (UTC)

That all only applies to quantum particles. For macroscopic objects, you're probably out of luck. Wormholes are probably your best hope. --Goodbye Galaxy (talk) 13:26, 27 October 2011 (UTC)

There might be some scope in Brane cosmology#Brane and bulk if your body can exit the brane and travel through the bulk before reappearing in the brane. That, at least, is one possible (if unlikely) explanation for the rather speedy neutrons we've been hearing about recently. --Tagishsimon (talk) 13:36, 27 October 2011 (UTC)

You're only probably out of luck with macroscopic objects. Such objects obey the same physics as "quantum particles". There is a chance that they will tunnel or otherwise exhibit non-classical behaviour. That chance is simply extraordinarily small; small enough that events like that are not likely to occur even over the whole lifetime of the universe.--Srleffler (talk)

There are a lot of ways to interpret this question, but I think it's best to say no. Continuity and locality are extremely important principles of modern physics, "even" quantum mechanics. There's no relationship between distinct points A and B that doesn't involve points in between them. -- BenRG (talk) 20:13, 27 October 2011 (UTC)

Night vision

Do people from the Far North tend to have better night vision than average? Seems to me that this would be highly advantageous, considering that it's dark for six months up there... 67.169.177.176 (talk) 06:08, 27 October 2011 (UTC)

This paper suggests that the high vitamin A content of Inuit diets improves night vision. The downside is that over-consumption of vitamin A can lead to some pretty nasty effects, including death in extreme cases. See Hypervitaminosis A and also Piblokto. SpinningSpark 11:14, 27 October 2011 (UTC) and 11:24, 27 October 2011 (UTC)

The six months of Polar night is a common mistake. For example here in Cambridge Bay the polar night lasts from 1 December to the middle of January but there is a period of twilight, at least 4+ hours, each day. On the other hand somewhere like Alert, Nunavut, much further north than Inuit live, the sun does not rise from 15 October until 27 February and there is no twilight from 29 October to 13 February, just over three months of darkness.

I've never noticed that anyone has better night vision up here, in other words they may have lost the ability. However, that could be down to most people living in houses with electric lighting and street lighting the same as anywhere else in the Western World. Also today the diet includes a lot more Western food than in years gone by coupled with a reduction in traditional diets. Also there is the period from 20 May to 25 July (Cambridge Bay) when the sun does not set at which point the night vision wouldn't help. CambridgeBayWeather (talk) 03:48, 28 October 2011 (UTC)

Thanks, but I was thinking more along the lines of genetic/congenital predisposition to better night vision. This is from my own personal experience -- I am originally from the Far North (although not that far north, where I used to live we didn't really have polar night in the winter) and when driving at night with only a crescent moon I can still see objects well beyond the range of my headlights (far enough that I can drive the daytime speed limit with complete safety, even on the freeway). But now I've been living in California for several years, and what I observe is that as soon as it gets dark everyone just starts driving so %#$@ing slow that it's downright maddening. What I was thinking about is whether there may be a link between the latitude of your birthplace and the ability to see well at night. But then again, maybe it's just me having the right genes for night vision? (BTW, I can also see just a tiny bit into the near infrared, which I found out when I first used a spectroscope in my high school chemistry class. Could there be a link between this and my night vision?) 67.169.177.176 (talk) 06:05, 28 October 2011 (UTC)

How much heat can Asbestos withstand?

Pure or mixed with concrete or other materials. By withstand, I mean both how hot till it burns and how hot till whatever it's protecting gets significantly hotter. Thank you. Cliko (talk) 07:09, 27 October 2011 (UTC)

Asbestos will not burn under any conditions, it will just melt if it gets hot enough. As for the second part, a sufficiently heavy layer of asbestos can protect human tissue against burns at temperatures of up to 1100 C or so (at least, that's what I've found so far). 67.169.177.176 (talk) 06:09, 28 October 2011 (UTC)

Oh, asbestos can burn, alright. Just introduce it to a sufficiently Lovecraftian chemical and stand well back! --Link ^(t•c•m) 07:28, 28 October 2011 (UTC)

Egyptian battery powered lamp

Some time ago this year, I watched a program on Discovery channel and observed an Egyptian tablet that was discovered with various figures and signs on it. The one of very interest to me , is the one figure, if it is the correct term, was one indicating a light globe, showing light and connected to something that looked like a power source, can it be a ‘battery’? It will be very interesting if you can verify if it was a burning light? Jack Koopman Pretoria South Africa. [email address removed]— Preceding unsigned comment added by 41.135.62.33 (talk) 13:38, 27 October 2011 (UTC)

Are you thinking of the Baghdad Battery? The closest thing to expert consensus is that it may have been used for electroplating, but probably not for light. SemanticMantis (talk) 14:18, 27 October 2011 (UTC)

There's also the Dendera light, which most experts believe is not depicting an electric light source, but which does bear a striking resemblance to modern light bulbs. Buddy431 (talk) 14:55, 27 October 2011 (UTC)

Hmmm, seems to bear a more striking resemblance to a surfboard, complete with the little cord keeping it connected to the surfer's ankle. A snake makes a cool decorative motif for a surfboard, but a lousy filament. Wnt (talk) 17:35, 27 October 2011 (UTC)

not a science question, but...

Is the mathematics taught in Thomas' calculus enough to understand concepts presented in "principles of physics" (by Haliday)?--Irrational number (talk) 15:01, 27 October 2011 (UTC)

By "Haliday" I presume you mean Halliday, Resnick, and Walker. My recollection is that the book is designed to be used by students who have completed a basic calculus course such as Thomas. There might be some use of differential equations in Halliday, I don't remember for sure, but in any case I think you would be okay. Looie496 (talk) 16:48, 27 October 2011 (UTC)

The old edition of Thomas I have, at least, does briefly cover ordinary differential equations, although not partial differential equations. Red Act (talk) 17:11, 27 October 2011 (UTC)

I think so. I don't actually have the Halliday book, but Thomas should be adequate as a mathematical prerequisite for pretty much any undergrad level physics textbook. You will need more math than what is in Thomas to understand all of undergrad level physics, but the additional math needed is in general presented within physics textbooks as it is needed. Not having actually looked at Halliday, I don't know for sure that that's the case with Halliday, but I would presume so just from the thoroughness suggested by the page count. Red Act (talk) 16:50, 27 October 2011 (UTC)

Human pheromone, sextual attractant

A QUESTION TO WIKIPEDIA:

THIS EMAIL IS MEANT TO BE SENT MAINLY TO WIKIPEDIA FOR INFORMATION ABOUT TRUE RELIABLE STRONG HUMAN PHEROMONE SEXUAL ATTRACTANT. ALSO ANY HELP OR CONTRIBUTION TO ANSWER FROM KIND ; READERS IS HIGHLY RESPECTED; THANKS FOR EVERY ONE. PLEASE READ BELOW. PLEASE RESPPOND BY EMAIL: <email removed>

Sir/Madam; DEAR WILIPEDIA; My question is about: True -not gemmics- RELIABLE sexual attractant for both sexes, THAT REALLY WORKS.

In particular; I do kindly seek correct information about HUMAN PHEROMONE:

1- IS THERE A REAL TRUE HUMAN PHEROMONE THAT DO REALLY WORKS IN ATTRACTING OPPOSITE SEX? ATTRACTING FEMALES AND/OR MALES? PLEASE KINDLY RESPOND AND PLEASE STATE IF ANY TRUE PHEROMONE EXISTS AND DOES WORK TO ATTRACT FEMAL/MALE SEXES TO EACH OTHERS. IF ANY, PLEASE TO ADVISE OF THE BRANDS IN THE MARKET AND OR ANY PERFUME THAT HAS IN ITS STRUCTURE PHEROMONE SEX ATTRACTANTS FOR HUMAN. (I did have read the articles in wikipedia but eventually could not make an idea if there is any or how it is made or of any brand to buy.

2- Please to advise of how human sex attractant is prepared/made. please to advise of the steps and the ingredients and the sources; whether plants, animals, amino acids, wastes, sweat, urine.....................etc. PLEASE TO ADVISE OF THE SITES OR WIKIPEDIA PAGES - OR KINDLY TO PROVIDE ADDITIONAL INFORMATION- OF HOW TO EXTRACT IT IN STEPS. 2- PLEASE TO ADVISE ABOUT THE MOST REIALBE VERSIONS/BRANDS OF THE HUMAN SEXUAL PHEROMONE THAT ARE AT PRESENT EXISTING IN THE MARKETS FOR SALE. WHETHER BLENDED IN PERFUME/S OR BY ITSELF; OR IN LOTIONS, CREAM, SPRAYS, DRINKS, FOOD, PAPER TISSUES, HAIR PRODUCTS OR BLENDED IN CLOTHES MAKING AND OTHER HUMAN ITEMS.

3- RE THE ABOVE REQUESTS, PLEASE EIHTER 2 PROVIDE THE SOURCE/s for THE SPECIFIC REQUESTED INFORMATION; WHETHER IN WIKIPEDIA pages ( but please to be addressing specifcally the requested information, and not general information), and/OR FROM OTHER SITES OR FROM ANY OTEHR SOURECES ACCESSIBLE BY NAVIGAGTING MAINLY THE INTERNET; OR BOOKS,SELLERS, MAKERS....ETC IN ADDTION, PLEASE TO HELP TO ADDRESS SPECIFICALLY THE REQUESTED INFROMATION REGRDIING: MAIN RESOURCES INITIAL PRODUCTS TO EXTRACT/PREPARE, HOW TO EXTRACT AND/OR PREPARE IT, WHERE TO FIND IT, BEST REPUTED SELLERS, BEST BRANDS IN THE MARKET THAT TRULY WORKING FOR HUMAN, AND WHICH BRAND THAT WAS TRIED AND/OR TESTED AND HAS REPUTAION THAT IT IS TURLY WORKING, IN ADDITION TO THE FORUMS>( THE (CUSTOMERS USED IT; BUT NOT SELLERS AND PROMOTERS), WHO TRIED IT AND HAAPPY ABOUT THE RESULTS AND THEIR FEEDBACKS AND RECOMMENDATIONS, IF ANY.

SIR/MADAM;

I AM SEEKING WIKIPEDIA TO GET RELIABLE TRUE OBJECTIVE SCEINTIFIC INFORMATION. IN MY VIEWS, WIKIPEDIA IS THE ONLY SOURCE THAT WOULD PROVIDE RELIABE, BOJECTIVE, SCIENTIFIC UNBIASED INFOMATION REGARDING ITS TOPICS. BUT THE INTRNET AND SELLERS' WEBSITES SEARCH IS NOT THE BEST APPROACH TO FIND RELIABLE INFORMATION RE THE REQUESTED PRODUCTS. THIS IS BECAUSE MOSTLY ANY PRODUCT INFORMATION USUALLY FOCUSSING ON ADVERTISEMENTS AND FOR MARKETING AND PROMOTIONS TO MAKE SALES. ANY INFORMATION WIKIPEDIA MAY PROVIDE RE THE ABOVE IS HIGHLY RESPECTED AND VALUED. THANKS FOR UR PROMPT RESPONSE

ADAM

PLEASE CC EMAIL TO: <email removed> <email removed>

cheers

ps: Sorry for any POSSIBLE semantic, grammatical and/or spelling mistake/s; if any. I am from a non-English speaking background. what can I do? NOT MY MISTAKE....... SORRY. — Preceding unsigned comment added by 49.2.26.145 (talk) 15:55, 27 October 2011 (UTC)

I've removed the e-mail addresses, which will only be used by spammer. We don't reply by e-mail on this board; if there is an answer, it will appear in the space below. --Mr.98 (talk) 16:19, 27 October 2011 (UTC)

I removed the hatnote - capital letters are unusual but not a crime - some of us grew up in an age of the Apple ][. I've added some extra linebreaks, because in Wiki formatting they're ignored if there's only one, unless the line begins with one or more colons. If the capital letters are that hard on your eyes feel free to lowercase the text. Wnt (talk) 17:06, 27 October 2011 (UTC)

In response to the question, the existence of pheromones seems to be a bit of a mystery - see [13] for an approachable reference. The best study I've seen is described in lay terms here [14].

I should add that I once worked around a colony of breeding mice now and then, and found the effect of their pheromones to be extremely distracting. They seemed to affect only female attractiveness, and particularly a sort of vaginal fixation which to me is quite atypical. Even women who were 100% not attractive to me were affected. I actually think that such pheromones might have a therapeutic function, because at the time I had had, for 30 years, the perception that women with east-Asian features were completely unattractive, but the pheromone made women like this attractive, and seemed to open my mind toward them permanently. I would love to see someone test these pheromones on pedophiles and see if they could be used to make them at least expand their preferences regarding age. Wnt (talk) 17:17, 27 October 2011 (UTC)

Human sexual response to odors generally varies vastly more in proportion to the respondent's predisposition, mood, attitude, other emotional factors, other sensory input (e.g. appearance of stimuli) and for females, estrous cycle state, than the odor itself. The human olfactory system has about 1,000 separate receptor types, all of which attenuate. There are very few bona fide hormones released by human males or females, and those that are do not have a substantial effect on sexual response of the opposite sex. Whether general body odor is attractive depends also on nationality, upbringing, etc.; the same can be said for perfumes and colognes. Dualus (talk) 20:10, 27 October 2011 (UTC)

metric system

Hello

I am not familiar with your community, so please excuse my foolish question, that for sure was asked many times before.

For example Parasaurolophus like many other articles contains a lot of redundant information about length an weight in metric system and in short tons, feet etc.. That is disturbing by reading this article.

Why do you not use the metric system alone? You could display information in any other system by using javascript via mousing over a value. (small box by mouse over)

Please do not let me be misunderstood. I am in respect for short tons and feed and inch and miles and landmiles and gallons. But please understand in metric system every value has a strong logic relation to an other value. For example 1 kg Water is 1 liter and needs a cube of 1 dm. (Stone has a factor approximately by 2,1 no big deal)

So if I read about a bone 1 m and 25 kg, I can imagine a good picture about other values like density (in stone) or stability. Even if this values are not provided I can make myself a good estimation about the Object that you like explain to me. :-)

Further more it seems to me a question of writing style. Providing values in many systems is like a over-decoration in regards of "political correctness". But the whole world cannot understand it ...

2.213.212.216 (talk) 17:27, 27 October 2011 (UTC)

This is the English Wikipedia. The US is a major English-speaking country, too big to ignore. Many people in the US don't understand metric units very well. Forcing the adoption of metric units is impossible, because whenever it is attempted, corporations make large campaign contributions to Congress critters, and the legislation is promptly watered down so that nothing happens. Jc3s5h (talk) 17:35, 27 October 2011 (UTC)

I understand your point. Whats about the javascript-solution that I proposed?

By the way, Wikipedia is not even a small entity. :-) YOU are in many aspects the unchallenged leading platform in science education in the world. Thats a responsibility I know. But it is also a chance to define standards. 2.213.212.216 (talk) 17:42, 27 October 2011 (UTC)

This isn't really a refdesk question, rather a WP:Village Pump kind of thing, but... It's not a matter of logic, but usefulness to the reader. For example, the air conditioners I've seen in the U.S. are rated in terms of BTUs. People who use them have their opinions about exactly how many BTUs they want to cool a given room. If you give a figure in watts, they won't be able to compare it to an advertisement or a product on the shelf - no approximate mental calculation is enough, they need the exact number. If they're going to need to make that mental calculation, it's only reasonable for them to post the results of it to the article in consideration of the next person. Wnt (talk) 17:45, 27 October 2011 (UTC)

OK, good point. :-) acclimatization. But it is also possible to acclimate to an other system. 2.213.212.216 (talk) 18:09, 27 October 2011 (UTC)

If you'd think logically for a second, 2.213.212.216, it would be easier if you could acclimatize to the wikipedia convention that units tend to be specified in metric and imperial, than that you seek to get all those who prefer imperial to acclimatize to metric. Your reservations concerning style and readability pale into insignificance with the more important objective of immediate access to immediately comprehensible material and without javascript accessibility no-nos. You see? --Tagishsimon (talk) 18:35, 27 October 2011 (UTC)

Its not about the question "How much is it in inch". It is about the Question "Can I make myself a scientific imagination of a described object using a logic toolbox." In other words: "Can I provide a writing style that makes indulgence, enjoyment and scientific stringence at the same time".

Lets make a thought-experiment: What would be if Wikipedia would say: "We always use the metric system in all languages, starting 2012!" Just for imagination, what would happen? I really want to know your opinions. :-)) 2.213.212.216 (talk) 18:03, 27 October 2011 (UTC)

If that was made a hard rule I think most Americans would stop using and contributing to Wikipedia, and seeing as Americans constitute the majority of users, editors and also donors, that would be the end of Wikipedia. Roger (talk) 18:16, 27 October 2011 (UTC)

Hm ... Maybe you are right.

That's ridiculous. For science-related articles, the metric system is already predominant. Anyone with a scientific or technical background is likely to be competent in the metric system and aware of its advantages. The bulk of those who find it annoying are those who specialize in entirely non-quantitative subjects, i.e. humanities people like me. But that's soft opposition. As for honest-to-god ideological metrication-haters, they're already more likely to spend their time huddled together at Conservapedia, Fox News Nation, World Net Daily, etc. Most ordinary people wouldn't care, and would get used to whatever standard. LANTZY^TALK 18:40, 27 October 2011 (UTC)

The advantages are somewhat overstated. The decimal stuff is useful for mental arithmetic in simple cases, but (i) other systems aren't that much harder, you just have to remember a few constants and (ii) most people don't do mental arithmetic anyway. For non-simple cases there's really no difference. Other advantages are things like not having to ask "now, is that a gram Avoirdupois or a gram Troy?" but those are somewhat marginal cases.

But the most important point is Wnt's below — Wikipedia is not a tool for reform. It's not anti-reform, just neutral. --Trovatore (talk) 18:54, 27 October 2011 (UTC)

Me thinks the People are loving this baby with all its peculiarity. :-)) *gg* But I am speaking as a german. People here would probably say "OK. If it is given as a hard rule we accept it. Enough for talking, lets go back to the workbench." 2.213.212.216 (talk) 18:35, 27 October 2011 (UTC)

I am not quite sure if I understand your points. But I am absolutely sure that this WP is not only the best collection of information. Your system of work is the future of science and education. You are not only collectors. Just wait 20 years of manpower and development. You will become a very important voice in history and thats ... for right. 2.213.212.216 (talk) 19:13, 27 October 2011 (UTC)

The rule would be reverted after vigorous protests. I think, 2.213.212.216, you have seen too few of wikipedia's holy wars if you estimate that the gnomes would simply shrug and get on with their work. --Tagishsimon (talk) 18:39, 27 October 2011 (UTC)

You are probably right. As I said I am not familiar with the indoor climate of Wikipedia.

But whats with small steps? The javascript-solution? Its fine. It makes things easy to editors ... every value is calculated automatically. And users can see how much is it in inch. 2.213.212.216 (talk) 18:48, 27 October 2011 (UTC)

Unlikely to work well or smoothly with screen readers. See Wikipedia:Manual_of_Style/Accessibility#Styles_and_markup_options We already have templates which convert one unit into another and display both, so that advantages is already catered for. --Tagishsimon (talk) 19:19, 27 October 2011 (UTC)

I think if a usable solution is desired, someone will appear to realize it. :-)) If you only want it. Do you want to go a small step in this direction? Imperial (and others) as a additional Information provided via javascript. In every case a unit is used. Thats a benefit for many articles. 2.213.212.216 (talk) 19:40, 27 October 2011 (UTC)

We try not to engage in magical thinking. We're content to follow screen reader technology, not provoke its extension. Really, this enthusiasm of yours is going nowhere. --Tagishsimon (talk) 19:46, 27 October 2011 (UTC)

The main thing is, Wikipedia doesn't have the purpose of improving how people measure things. It just prints what is known, as people know it. Get people to stop using non-metric units and Wikipedia articles will follow. Wnt (talk) 18:43, 27 October 2011 (UTC)

YOU are the most powerful entity in education. In my point of view there is absolute not reason to underestimate yourself. If you think something should be chanced by good reasons, you are the people who can do it. Nobody else could do it like explained above. Am I wrong with that? 2.213.212.216 (talk) 18:56, 27 October 2011 (UTC)

You are wrong. The most easy thing would be for you to acclimatize yourself to wikipedias valid use of the metric (imperial) convention, than for you to seek to get wikipedia to acclimatize the views of millions of people who have one or other first preference. We are not here to proselytize your view of what would be best and don't agree the supposed benefit is worth the inconvenience to users. --Tagishsimon (talk) 19:22, 27 October 2011 (UTC)

It bothers me that our IP editor is being pushed in a certain direction because it would be the easiest path. Sometimes it's better to do the hard thing now to make the world a better place in the long term. Most of the world that was imperial successfully converted to metric during the last century by talking a long term view. Sadly, modern politics is built on the short memories of voters, so the USA probably won't metricate any time soon, but it's disappointing to see "take the easy path" becoming dogma in the world's most popular science resource. HiLo48 (talk) 19:51, 27 October 2011 (UTC)

It's not about easy. We're not supposed to do it, period. This is part of WP:NPOV and is an absolute fundamental idea of the project. --Trovatore (talk) 20:02, 27 October 2011 (UTC)

If wikipedia were to decide to use metrics-only, it could trigger the mother of all edit wars. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:44, 27 October 2011 (UTC)

What is your weight in Newtons? Wikipedia does well enough without trying to be entirely "metric" to be sure. Give then a centimeter and they will take a kilometer, as the adage goes. Collect (talk) 22:56, 27 October 2011 (UTC)

I'm drifting off-topic here, but weight in that sense really means "mass". A person's weight, in the sense of how much force he exerts on what he's sitting on, has always been secondary except to chair-makers and so on; what has always mattered most is the quantity of matter, and this has traditionally been called "weight". Physics teachers somewhat arbitrarily insist on using weight to mean exclusively force, I think mostly to emphasize to their students that the gravitational force and the quantity of matter are not the same thing, but this linguistic distinction has no historical basis. --Trovatore (talk) 00:12, 28 October 2011 (UTC)

Let's stick to God's units. Count Iblis (talk) 23:47, 27 October 2011 (UTC)

Cubits, talents, like that? --Trovatore (talk) 01:09, 28 October 2011 (UTC)

Actually it would be fun to translate everything to the talent–cubit–day system and see how things shake out. What would the unit of capacitance be, for example? The farad is inconveniently large; who knows if this one would come out more reasonable. --Trovatore (talk) 01:12, 28 October 2011 (UTC)

I have an idea: 1 planck length = 1 splinter, 10⁹ splinters = 1 plank, 10⁹ planks = 1 pallet. Plasmic Physics (talk) 02:11, 28 October 2011 (UTC)

Everything is dimensionless, but to make use of this fact one needs to correct for the fact that we've assigned units to quantities in an inconsistent way. Correcting for this amounts to switching to Planck units (up to some arbitrary overall scale factor). Count Iblis (talk) 03:50, 28 October 2011 (UTC)

A megasplinter! Plasmic Physics (talk) 05:28, 28 October 2011 (UTC)

On a more serious note, we really ought to use decimetres more- the centimetre, like its humanistic counterpart, the digit, is not appropriate for most of the uses it is put to. Nevard (talk) 02:37, 28 October 2011 (UTC)

October 28

How do human beings copulate?

On Youtube, I sometimes watch videos of animals mating with each other. I have seen a male dog mate with a female dog. The female dog is standing on all fours. The male dog rests on top of the female dog's back and mates with her. In frog species, the female frog lays hundreds or thousands of eggs in the pond water to prevent desiccation and the male frog fertilizes all the eggs in the water. Different animals have different ways to mate with one another to bring forth the next generation.

Simply put, what is the normal,natural human mating position? I am not sure if the female is turned away from the male or facing toward the male in the mating process. — Preceding unsigned comment added by 75.185.79.52 (talk) 02:00, 28 October 2011 (UTC)

I'd suspect that face-to-face is probably more common, but both work, and it comes down to cultural norms, and to individual preference. I think it is probably both 'normal' and 'natural' to experiment, try a bit of variety, and see what suits the couple concerned. AndyTheGrump (talk) 02:25, 28 October 2011 (UTC)

Humans show a remarkable capacity for play or experimentation into adulthood; they also have a major difference from animals in the form of culture. Humans fuck in different ways for different cultural reasons. Some times these cultural reasons are large, like American television authorising certain ways of negotiating sex. Some times these cultural reasons are small, like peer-to-peer advice, or the private negotiation of personal preference. As far as the wide variety of manners in which people fuck, they do it standing, seated, lying down on their front back or side. They face each other, they turn away, they face each other sideways. If there is one way to characterise human copulation, it is that humans copulate in exhaustively permuted ways. Fifelfoo (talk) 02:33, 28 October 2011 (UTC)

Both; see sex positions. It... is illustrated. Dualus (talk) 02:44, 28 October 2011 (UTC)

How do humans compare with other hominids or apes or monkeys or primates? — Preceding unsigned comment added by 75.185.79.52 (talk) 02:56, 28 October 2011 (UTC)

As far as I'm aware, only Bonobos (pygmy chimpanzees) regularly copulate face-to-face, though apparently Gorillas have been observed doing it occasionally. Bonobos are unusually 'promiscuous' and seem to copulate as a method of communication rather than procreation (but then, so apparently does Homo sapiens)... AndyTheGrump (talk) 03:10, 28 October 2011 (UTC)

Molecular bonding II (Repost)

What does the MO diagram for monomeric beryllium hydride look like?

This was my idea:

__ __ __  3×2σ*
     __      1σ*
↑↓ __ __  3×2σ = 2p_z¹(Be) + 1s¹(H2)
    ↑↓       1σ = 2s¹(Be) + 1s¹(H1)

    ↑↓       n = 1s²(Be)

This was not my idea:

__ __ __  3×2σ*
__ __ __  3×2σ
    ↑↓       1σ* = 2s¹(Be) + 1s¹(H2)
    ↑↓       1σ = 2s¹(Be) + 1s¹(H1)
    ↑↓       n = 1s²(Be)

This is my idea:

  __     2σ*
__ __  2×1σ*
  __     2σ
↑↓ ↑↓  2×1σ = 2s¹(Be) + 2p_z¹(Be) + 1s¹(H1) + 1s¹(H2)

  ↑↓     n = 1s²(Be)

If this is true, then why is there no sp mixing to allow for the diberyllium molecule? Plasmic Physics (talk) 05:16, 28 October 2011 (UTC)

I have not heard of group theory or SALCs before in any of my chemistry papers. Plasmic Physics (talk) 05:16, 28 October 2011 (UTC)

Sequentially precipitating certain metal salts out of a solution

I have a vague memory from high school chemistry that we had a table showing that one could precipitate for example copper out of a solution by adding an iron salt (or was it zinc?). The table was in the form of a "sequence": Add A to precipitate B then add C to precipitate B then add D to precipitate C.... I can't remember what the table was called so I can't search for it. Roger (talk) 07:10, 28 October 2011 (UTC)