Wikipedia:Reference desk/Archives/Science/2011 October 28

= 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)


 * I just want to add in, there is no one "normal, natural" position. Every historical record we have points to people in all cultures, at all times, doing it every which way. At certain very extreme times, various cultures have proclaimed one way of doing it to be the only acceptable way by their standards, but there is absolutely no reason to privilege such occasional proclamations over the observed variation. Seeking a "normal, natural" position is a fool's errand at best. You will not find it for it does not exist. To editorialize a bit: that we have such a variety of sexual practices, while much of the animal kingdom has relatively restricted means, is yet another reason it's great to be a human being, and not, say, a dragonfly. Let's not be so quick to embrace the rigid dragonfly as an ideal. --Mr.98 (talk) 11:24, 28 October 2011 (UTC)
 * Embracing rigid dragonflies may be illegal in many jurisdictions... but, whatever floats your boat... -- Jayron  32  12:51, 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 = 2pz1(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) + 2pz1(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)
 * If you have not heard of it, why not do some reading on the subject. Linear combination of atomic orbitals is a good place to start, and it will take you though some specific Linear combination methods if you follow the links.  -- Jayron  32  11:55, 28 October 2011 (UTC)

I have heard of LCAO. I combined the orbitals according to my understanding of LCAO, which is why I need onfimation. Plasmic Physics (talk) 12:45, 28 October 2011 (UTC)
 * Try Google: . There's This diagram I found, and there is a youtube video in there titled "MO of BeH2" which may be useful to you.  -- Jayron  32  14:52, 28 October 2011 (UTC)

This is my new idea:

__ __ 2×1σ* = 3s0(Be) + 3pz0(Be) + 2s0(H1) + 2s0(H2)

__ __ 2×n = 2px0(Be) + 2py0(Be)

↑↓ ↑↓ 2×1σ = 2s1(Be) + 2pz1(Be) + 1s1(H1) + 1s1(H2)

↑↓    n = 1s2(Be)

Is this true? Plasmic Physics (talk) 05:55, 29 October 2011 (UTC)

I couldn't get the image to load, but I managed to watch the YouTube clip. This is the new diagram incorporating degeneracy. How about the second question? Plasmic Physics (talk) 04:37, 30 October 2011 (UTC)

Being a chemistry student, I just spent about an hour trying to solve this problem using my textbooks, but I doubt you can find a definite answer without actually calculating the MO`s, as our (German) textbooks only deal with even numbers of atoms in molecules here. And I`m afraid calculating orbitals is currently beyond my abilities... Phebus333 (talk) 19:42, 1 November 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)


 * Ferrous sulfate works, to precipitate metallic copper. Plasmic Physics (talk) 10:10, 28 October 2011 (UTC)


 * Then what do you use to get the iron out? I'm looking for the entire sequence for all the metals from Li to U. In class we were given a "witches brew" and our task was to identify all the metals in it through a sequence of precipitations. Roger (talk) 10:48, 28 October 2011 (UTC)


 * Oh, you want all the copper to precipetate out? Well, then you have to use something like sodium hydroxide, then you'll precipitate all of it out. Otherwise it just disproportionates. Plasmic Physics (talk) 12:14, 28 October 2011 (UTC)


 * Read qualitative inorganic analysis. Graeme Bartlett (talk) 12:15, 28 October 2011 (UTC)


 * Yay! At last someone groks what I'm looking for. Thanks! Roger (talk) 12:20, 28 October 2011 (UTC)

to find out a pill cant find its use
i have a pill 263 on one side and the other side is the manufacturer mark i believe looks like a wide u with a line above it its oblong and a faint color of blue green i would like to find whats the drug or use found in cabinet i thank you for your time i looked for some images and the markers mark looked like a company named activus elizabeth ? not sure how it was spelled  well i hope you can find info thank you  — Preceding unsigned comment added by 71.231.228.250 (talk) 08:23, 28 October 2011 (UTC)
 * If it is just a random pill you found flush it down the toilet and forget about it. If you have a genuine reason to know what it is, take it to a pharmacist. Roger (talk) 08:55, 28 October 2011 (UTC)
 * Flushing drugs down the toilet is not environmentally friendly. The ideal way to dispose of drugs is to use a community drug take-back program.  If no such program is available locally, the recommended procedure for disposing of unidentifiable drugs is to mix them with an undesirable substance such as used coffee grounds or kitty litter, put the mix in a sealable bag, and put the bag in the trash.  Red Act (talk) 09:30, 28 October 2011 (UTC)
 * Drugs.com has a Pill Identifier.
 * But I agree with the above comments. Even after you identify it you shouldn't actually use it. If nothing else you don't know when its expiration date is. APL (talk) 10:11, 28 October 2011 (UTC)

Red shift due to gravity, where does the energy go?
Lets say you are on a planet with no atmosphere. You shoot a laser out into the sky, and of course the light emitted is red shifted, so the photons lose energy. So where does that energy go? What does it turn up as? ScienceApe (talk) 17:50, 28 October 2011 (UTC)


 * Gravitational potential energy. Dauto (talk) 18:02, 28 October 2011 (UTC)


 * So you're saying the gravitational force increases? ScienceApe (talk) 19:44, 28 October 2011 (UTC)


 * I'm saying the gravitational potential energy increases because the photon has a relativistic mass given by the formula E=mc^2 and therefore it has a gravitational potential energy associated with moving that mass through a gravitational field. See my comment below for a more subtle interpretation (it requires deeper understanding, is harder to comprehend but is much more insightful). Dauto (talk) 20:12, 28 October 2011 (UTC)


 * I'm not following you. I don't understand either explanation you are giving. In layman's terms, does the gravity field become stronger? ScienceApe (talk) 00:40, 29 October 2011 (UTC)


 * In layman's terms, no the gravity doesn't change, the gravitational potential energy (read the link) changes. Read Gandalf's comment bellow. If you shoot a cannon ball up in the sky, it slows down as it goes up. Where does the energy go? It turns into gravitational potential energy. Dauto (talk) 14:58, 29 October 2011 (UTC)


 * Are you basically saying that hypothetically speaking, if the light that was shot out into space was ever deflected and sent back to the planet, it would just be blue shifted, and that's where the energy is conserved? ScienceApe (talk) 01:00, 29 October 2011 (UTC)


 * I'm saying the energy is always conserved if you also include potential energy along with the kinetic energy (A photons energy is a form of kinetic energy). Dauto (talk) 15:06, 29 October 2011 (UTC)


 * Ok, but what about when a black hole evaporates due to hawkings radiation? When it finally evaporates, it will release whatever mass it has left as energetic gamma rays. These photons will be redshifted, but there's no more singularity there to increase their gravitational potential energy. ScienceApe (talk) 16:09, 29 October 2011 (UTC)


 * Why would the last photons be redshifted since, as you said, there's no gravitational well left to redshift them? These last photons won't be redshifted. Dauto (talk) 16:15, 29 October 2011 (UTC)


 * They would. Or at least some of the photons would be redshifted. ScienceApe (talk) 17:31, 29 October 2011 (UTC)


 * Here, read more: http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2010_December_11#Mass_Energy_and_Black_Hole_evaporation ScienceApe (talk) 17:40, 29 October 2011 (UTC)


 * Who are trying to quote from that thread? I hope it's not Ariel since what s/he said makes no sense. Dauto (talk) 13:50, 30 October 2011 (UTC)


 * Ariel mostly yes. He/she might be wrong though, I'll concede that. Still, light is being radiated away even before the singularity has evaporated completely, so that light is going to be red shifted. After reading that discussion again though, it's possible that the mass of the singularity might exceed the mass of the matter that was actually compressed because the gravitational energy of the matter adds to the mass of the singularity. If all the mass is radiated away as photons, it might still equal the mass of the matter that was compressed in the first place even after being red shifted. This is just my guesswork though. ScienceApe (talk) 23:43, 31 October 2011 (UTC)


 * Alternatively you can simply realize that gravitational redshift is equivalent to a Doppler redshift in which the photon energy is different depending on the observer because the observers are moving relative to each other. Dauto (talk) 18:24, 28 October 2011 (UTC)


 * You are on a planet with no atmosphere. You throw a rock into the sky. The rock slows down. Where does it's kinetic energy go ? Same place as the photon's lost energy. Gandalf61 (talk) 09:28, 29 October 2011 (UTC)

What if the best lie detectors only worked on people who haven't been tortured?
What if it were possible to use a fMRI scanner to interrogate uncooperative victims suspects as accurately as cooperative victims, but only if they haven't been tortured by their captors? Would making the suspects think that they have returned to their allies help? Dualus (talk) 20:35, 28 October 2011 (UTC)
 * What if bosses only paid employees who did bad things? Would punching your boss in the nose earn you a raise? Looie496 (talk) 21:32, 28 October 2011 (UTC)
 * Is that supposed to be analogous some way? Dualus (talk) 22:40, 28 October 2011 (UTC)
 * I think he's trying to say, "that's a lot of 'what ifs' you've got there." --Mr.98 (talk) 22:43, 28 October 2011 (UTC)


 * First sentence: then I guess you wouldn't want to torture them, eh? Second sentence: I don't see why that would follow; you just said they didn't need to be cooperative. If you're not torturing them, then it's gravy no matter what they think, no? --Mr.98 (talk) 22:43, 28 October 2011 (UTC)


 * I don't know why you included the "if they haven't been tortured" part. And I don't know why victims would be uncooperative. The question is somehow confusing. Anyway, I don't believe any mechanical lie detector works better than experienced interrogators, and I don't believe you can extract more truthful information with torture than without it. Quest09 (talk) 01:18, 29 October 2011 (UTC)


 * Here's an example of a lie detector that actually works. (More like a truth serum, really...) 67.169.177.176 (talk) 03:54, 29 October 2011 (UTC)


 * Sorry I screwed up the question. Fixed s/victims/suspects/ Dualus (talk) 09:48, 29 October 2011 (UTC)


 * No you didn't fixed it completely. Why "cooperative victims"? Quest09 (talk) 10:13, 29 October 2011 (UTC)
 * There is more than that screwed up about the question. You need to consider what the purpose of interrogation and debriefing actually are, what flavour of information you're expecting to elicit from your "subject" and how you're going to validate and corroborate both your subject and any information you elicit from them.
 * ALR (talk) 09:52, 29 October 2011 (UTC)
 * Why is that my job? That's what the criminal justice system is for. Dualus (talk) 18:23, 29 October 2011 (UTC)
 * Your question displays your own bias.
 * From a practical perspective there is a difference between debriefing and interrogation, although they are complementary. But the point I'm trying to make is that the purpose of debriefing and interrogation is to elicit information from the subject.  To do that one must have an understanding of what type of information one is anticipating and as a result identify the most appropriate tools to elicit that.
 * Incidentally most of the points that I made apply as much to military debriefing and interrogation as the law enforcement environment.
 * ALR (talk) 20:12, 29 October 2011 (UTC)
 * How do you think I am biased? Dualus (talk) 00:26, 31 October 2011 (UTC)

Contact lens + eyeglasses?
Does anyone wear contact lenses and eyeglasses at the same time? For example, if their prescription is -14.50 and the contacts go only up to -12.00, roughly what kind of glasses can they wear to produce the same vision? 66.108.223.179 (talk) 21:26, 28 October 2011 (UTC)


 * I don't know the specific technical question, but yes, lots of people wear both, especially as they get into late middle age and their near vision starts to deteriorate. My mother wears contacts for her distance vision, but needs reading glasses for her near vision. It's not uncommon in that instance. I've never heard of someone wearing contacts and glasses just to up their prescription in one direction, though, but I've never made a study of it. --Mr.98 (talk) 22:33, 28 October 2011 (UTC)


 * According to Lens (optics), the combined focal length of a pair of thin lenses of focal lengths f1 and f2 that are separated in air by a distance d is


 * $$\frac{1}{f} = \frac{1}{f_1} + \frac{1}{f_2}-\frac{d}{f_1 f_2}.$$


 * The diopters given as a lens prescription is the reciprocal of the focal length of the lens, measured in meters. In the case of eyeglasses, the separation between the cornea and the eyeglasses lens is called the vertex distance, which is usually 14mm.  So plugging in -14.5 for 1/f, -12 for 1/f1, and 0.014 (14mm expressed in meters) for d, and solving for 1/f2 gives 1/f2 = -2.14.  So to get a total of -14.5 diopters when wearing a contact lens of -12 diopters, the eyeglass lens would need to be -2.14 diopters.  Red Act (talk) 23:11, 28 October 2011 (UTC)

Yes, i have a classmate that wears glasses and one contact lense because his glasses would tip to the right because of thickness if he didnt use contacts. Meaning his eyes are so messed up. — Preceding unsigned comment added by 203.112.82.128 (talk) 14:23, 29 October 2011 (UTC)

Yes, until earlier this year I used contact lenses of -6.5 with reading glasses of +2. Nowadays I use disposable varifocal contact lenses, so I don't need to carry reading glasses any more. -- Arwel Parry (talk) 14:35, 29 October 2011 (UTC)


 * Some people wear contact lenses (with diopters) with tinted sunglasses (without dioptres). I for one have not tried that yet, but I would if I could wear contacts more.  Also, I have worn contacts with ski goggles, but that's not the same (I normally wear the ski goggles over glasses).  &#x2013; b_jonas 20:44, 31 October 2011 (UTC)

Chlorine trifluoride
What's the best way to fight a chlorine trifluoride fire? According to the article, sand won't work, CO2 won't work, inert gas won't work, fire blankets will just burn right through, foam won't work, halon won't work, and water will just make things worse. (Kinda makes me glad that we don't have to work with this devil's venom at the refinery.) So if none of these things work, what does? 67.169.177.176 (talk) 22:23, 28 October 2011 (UTC)


 * The advice from the Occupational Safety and Health Adminsitration is pretty much to let it burn. Unruptured containers can be kept cool with hoses but ones that are already burning will continue to do so unless the fire runs out of fuel, which is unlikely (chlorine triflouride is the oxidizing agent, not the fuel).  Spinning  Spark  22:48, 28 October 2011 (UTC)
 * The safety sheet I found says much the same. Rather amusingly, it describes it as "non-flammable" (which is technically true - it takes the role of oxygen, not fuel, in the combustion). It doesn't give a great deal of advice on how to put out fires, but concentrates on how to avoid being killed by them and how to stop them getting worse. I would guess that these fires don't last particularly long - once all the chlorine trifluoride has been used up the fire will either go out or it will just be a normal fire and you can put it out in normal ways. In the first aid section, it says that if you get it on your skin then you should use water to wash it off, but you need to use a hell of a lot of it (and keep going for several hours, unless you have some "iced alcoholic or aqueous zephiran chloride solution or Hyamine 1622 solution" that you can apply, although I'm not sure what that does). --Tango (talk) 23:17, 28 October 2011 (UTC)
 * Wait a minute... If I get this stuff on my skin, wouldn't it set me on fire? After all, according to the article, ClF3 is "hypergolic with cloth, wood, and test engineers", and I definitely fall into this last category. 67.169.177.176 (talk) 01:51, 29 October 2011 (UTC)
 * That seems to be a direct quote. It seems to react spectacularly with most organic materials, which presumably includes engineers. I'd not recommend trying it to see if it is true... AndyTheGrump (talk) 02:00, 29 October 2011 (UTC)
 * Yes, I think that's why it reacting violently with the water you use to wash it off is considered worth it - it's going to be reacting violently with your skin if you don't! --Tango (talk) 02:15, 29 October 2011 (UTC)
 * And once the ClF3 is used up, the excess water will put out the flames. All the same, third-degree burns are very likely in either case. 67.169.177.176 (talk) 03:52, 29 October 2011 (UTC)
 * Evidently, the answer to the original question, which was what was "the best way to fight a chlorine trifluoride fire" is probably to run like hell, and let someone else deal with it. For an inanimate substance, it seems to have a great deal of malevolence... AndyTheGrump (talk) 05:11, 29 October 2011 (UTC)

Find an agent that acts as neutralizer to fuel for the fire and thus it will go out — Preceding unsigned comment added by 109.224.25.14 (talk) 08:04, 29 October 2011 (UTC)


 * What is a neutraliser? Plasmic Physics (talk) 08:53, 29 October 2011 (UTC)
 * I think he/she meant a reaction inhibitor... 67.169.177.176 (talk) 23:58, 29 October 2011 (UTC)


 * There would be a few safe gasses that would disperse this, eg carbon tetrafluoride or solids that would not react, such as calcium fluoride, or solids that react to form another solid like slaked lime but it is probably safer to let it burn off as it boils at 12° and so will be very hard to contain. Graeme Bartlett (talk) 11:23, 29 October 2011 (UTC)


 * Do really want to disperse this? I would definitely want to contain the pillage, instead of creating a disperse cloud of highly corrosive gas. Calcium fluoride would only low down the reation, but would not stop it, it doesn't form an air tight seal. Plasmic Physics (talk) 00:29, 30 October 2011 (UTC)

contact lenses
hello there. my friend has said that since (in our area) contact lens prescriptions are incremented in .5 dioptres whilst glasses prescriptions are by .25, when she wears her contacts she has trouble driving at night in areas she doesn't know because she "can't read the street signs until [she] gets right up to the street". She's told me she has a fairly strong prescription (I don't know specifically but having peeked through her glasses I estimate it is at the absolute most -5 and probably more like -3); but would being undercorrected .25 dioptres really cause such a large difference in how well she can see? Or am I wrong in naively subtracting applied prescription from true prescription to find how someone sees? danke. 196.28.228.254 (talk) 23:45, 28 October 2011 (UTC)


 * I doubt .25 dioptres would make much difference. Since it only happens at night, I'm guessing it's not a simple issue of myopia. There are various conditions that can affect night vision. She should speak to her optician. --Tango (talk) 00:12, 29 October 2011 (UTC)


 * She should probably speak to her optometrist (who will diagnose the problem), rather than her optician (who will supply the glasses prescribed by the optometrist). Although admittedly, the terminology may vary by country. Mitch Ames (talk) 23:28, 29 October 2011 (UTC)

This is indeed a simple case of myopia. During the day our pupils contract and make focussing less important, just as reducing the lense aperture on a camera increases depth of field. I have a prescription of -4 dioptre for reading and -6 for distance. But during the day I wear my reading glasses all the time, as I can barely tell the difference. But at night wearing my distance specs for driving is absolutely essential. What is interesting is that at night, things don't look blury, they look darker. — Preceding unsigned comment added by 121.215.50.144 (talk) 02:53, 29 October 2011 (UTC)


 * I can say for a fact that contact lens prescriptions are incremented by .25 diopters from common U.S. sources (e.g. Wal-Mart). This is of course not a law of science - any manufacturer can make either glasses or contacts with any level of difference between them.  There are many potential causes for poor vision and we can't diagnose her particular problem (just for examples - astigmatism, pannus, onset of diabetes, vitamin A deficiency, macular degeneration - and that's by no means a complete list; seriously, it's beyond our powers).