Wikipedia:Reference desk/Archives/Science/2012 May 31

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May 31[edit]

Animal bones[edit]

After an animal like cattle is slaughtered for its meat and skin, what happens to the bones? Can they be used in any useful way or are they just thrown out? ScienceApe (talk) 05:08, 31 May 2012 (UTC)

Cattle bones can be used to make bone char, or protein component can extracted for use in making gelatin. Some people also make jewelry out of it. I don't know though what percentage of cattle bones are actually put to each use, or whether some of it is simply disposed of. Someguy1221 (talk) 05:41, 31 May 2012 (UTC)
Some goes to making bone china, but not much these days I fancy. Richard Avery (talk) 06:50, 31 May 2012 (UTC)
You can also make Bone meal. As our article mentions, used as fertiliser and in the past as animal feed, but that largely went out of fashion after Bovine spongiform encephalopathy. Our article mentions Meat and bone meal which obviously also contains some bones has some other purposes. I may be mistaken, but my impression is nowadays very little is thrown away. (Our Environmental impact of meat production doesn't really discuss this.) Nil Einne (talk) 09:11, 31 May 2012 (UTC)
And, of course, beef stock, which is useful for many sorts of foods. (talk) 13:18, 31 May 2012 (UTC)

For a skyscraper window washer, falling ....[edit]

How many floors (lets say at 3.6m or 12' high) would it take for a window washer falling from a skyscaper to reach terminal velocity so that any further floors dont make any difference? I ask because of this video [1] which speaks of a man falling 47 floors and surviving, even to [allegedly] a full recovery. Benyoch ...Don't panic! Don't panic!... (talk) 05:47, 31 May 2012 (UTC)

It would depend somewhat on the weight of the person and on the altitude. Atmosphere at higher altitude is thinner, and would give less resistance. The weight of the person matters because surface area (which catches the wind) is less relative to weight in a fat person than a thin one. There might also be other factors, such as variation in gravity at different points on the earth, and whether you are near the poll or equator. In addition, there are the physiological differences between people -basically how tough they are- that make a difference. Also the angle at which they hit the ground, and the tension in their muscles at the time (drunks survive accidents). So you can't pinpoint an exact number, but you might get fairly close. Someone else here can tell you about how fast he was going. He might have been cushioned by falling on top of his brother who fell with him. BeCritical 06:04, 31 May 2012 (UTC)
That was a fun simulation to write. Thanks for the question. Assuming that terminal velocity is 55m/s and that air resistance is proportional to the square of velocity, your acceleration becomes negligible after about 9 seconds, having fallen about 300 meters. Assuming 47 floors at 3.6m per floor, my simulation still shows him going 46m/s when he hits the ground after falling for a little over 6 seconds. If anyone asks why I bothered running a simulation, it's because it was easy to make and I don't remember calculus. Someguy1221 (talk) 06:09, 31 May 2012 (UTC)
Shape of the person and their clothing would also alter terminal velocity. (talk) 10:08, 31 May 2012 (UTC)
In a real case scenario, other factors can help you survive. Hitting your leg on a marquise, falling on a tree, above a car, all these things might help you survive, even terminal speed. OsmanRF34 (talk) 17:03, 31 May 2012 (UTC)
I do remember that if you fell off Burj Dubai you'd slow down before hitting the ground, due to entering thicker air. Pretty interesting. (talk) 23:25, 3 June 2012 (UTC)

In E = Mc2, Why c?[edit]

In Einstein’s equation, E=Mc2 , c is a constant representing the speed of light. It has always seemed odd to me that nature would use this specific value for both the speed of light and the immense value by which mass is multiplied to equal the amount of pure energy the mass contains.

As far as I know, neither nuclear fission nor fusion are fundamentally dependent upon the acceleration of mass to anything approaching c, let alone c2 (which, of course, would be impossible). Therefore, why does this specific constant pop up in an equation that calculates the amount of energy locked up in mass?

I am neither a physicist nor mathematician, so, if at all possible, could someone attempt a non-mathematical explanation? Honeyman2010 (talk) 06:55, 31 May 2012 (UTC)

Well, what distinguishes special relativity from Newtonian physics is the existence of a special speed, c, which shows up all over the place. Among other things it's the speed at which light propagates, but that's not fundamentally what it is, and it was probably a mistake to name it "the speed of light".
Because c is so fundamental it's often seen as an indication of the "correct" units to use for distance and time. E.g., if you use seconds for time then you should use light-seconds for distance, so that c = 1. Then the equation is just E = m and says that energy and mass are the same thing. -- BenRG (talk) 07:04, 31 May 2012 (UTC)
Yeah, that makes a lot more sense. E=M. Of course, why didn't we use that from the start? Perhaps coz the c in Einstein's equation gives us the info that there is a hell of a lot of energy in a small amount of mass, something that E=M does not. Myles325a (talk) 07:53, 4 June 2012 (UTC)

And if you don't like that explanation, it's also an unavoidable consequence a simple derivation of the equation, which you can see here. Someguy1221 (talk) 07:09, 31 May 2012 (UTC)
See also physical constant.--Shantavira|feed me 07:43, 31 May 2012 (UTC)
It's sort of the same thing as the way π shows up all over the place in many different sorts of maths. And how the golden equation exists. It seems to suggest something fundamental about reality, perhaps, but we start to leave science behind when we ask "why" in these cases. (talk) 13:13, 31 May 2012 (UTC)
One does not necessarily leave science to fully understand how certain values relate to one another. The speed of light is not just the literal speed of light (it is that, of course), it's some sort of deep reflection of how physics is put together. We may yet understand that, fully within the confines of scientific thought, without recourse to mythology. --Mr.98 (talk) 13:41, 31 May 2012 (UTC)
Mythology? Since when is philosophy mythology? Since when are interesting mathematical ideas mythology? Are you under the impression that everything divides into 'science' or 'mythology'? I didn't think you were, but I don't see how else to parse your comment. (talk) 17:02, 31 May 2012 (UTC)
To give a slightly different spin on what others have said, this equation does not appear in Newtonian mechanics. It only turns up when we start dealing with special relativity, a more refined theory of how motion works, that gives accurate answers in a wider variety of situations. The important assumption that appears in special relativity, but not Newtonian dynamics, is that if an object is moving at speed c according to one inertial observer (an observer travelling at a constant speed in a constant direction), then it will be moving at speed c according to any inertial observer. This assumption is needed for electromagnetism to work the same way according to any inertial observer, and we know it does due to various experiments like the famous Michelson-Morley experiment. The assumption turns out to have lots of interesting consequences, including your equation. Just to point out a possible misunderstanding in your question: it sounds like you are saying that it would be impossible for an object to accelerate to a speed of c^2 because that value would be greater than c. Instead, this is impossible because it doesn't make sense to interpret c^2 as a speed - c^2 is measured in m^2/s^2, while speed is measured in m/s. Saying an object moves at speed c^2 would be a bit like saying that a container holds 5 minutes of water. The units we measure speed in are arbitrary - we could use a system of units in which c=0.5, and the numerical value of c^2 in that system of units would be less than that of c. (talk) 15:40, 31 May 2012 (UTC)
Expanding (perhaps a bit tangentially) on 130.88's final point, it's worth noting that there are a number of systems of so-called natural units used by physicists that assign simple values (usually exactly 1) to commonly-used physical constants. In Planck units, for instance, all of c, G (the gravitational constant), h-bar (the reduced Planck constant), and kB (the Boltzmann constant) are numerically equal to 1. TenOfAllTrades(talk) 15:54, 31 May 2012 (UTC)

You can also derive this starting from E = m, see here. To me this argument makes more sense as obviously c should be put equal to 1 in special relativity. There is no good reason within special relativity to have different units for distances and time intervals. Then to explain how to put back c when you are not allowed to use dimensional analysis, is what needs to be explained as I do on that page. Count Iblis (talk) 17:02, 31 May 2012 (UTC)

Every time that Count Iblis discusses his theory for measuring time- and space- in common units, I feel compelled to bring up several examples where time and space are not symmetric. You can use any unit you like, and you can set c == 1 (in units of some_spatial_interval_per_some_time_interval), but you can't ignore that it is not equal to one: it has units. If you ignore those units, then you break almost all of physics. Time and space are not "identical" types of physical quantities; at least, not for any reasonable definition of "physical." Time and space behave differently in almost every equation we use to describe physical phenomena; equivalently, almost all phenomena are described by equations that are not symmetric over an interchange between time- and space- variables. Nimur (talk) 01:09, 1 June 2012 (UTC)
I don't agree that considering space and time to have the same dimensions would break any laws of physics. It would merely break conventions. There is no problem whatsoever with doing physics without any units or dimensions, at least not theoretical physics. You can never do an experiment that could settle if two arbitrary quantities X and Y are dimensionally incompatable. That they are physically different is a vague ill defined qualification, you could also say the same thing for kinetic and potential energy. Count Iblis (talk) 01:31, 1 June 2012 (UTC)
And note that it's not my theory, it's the same position Michael Duff takes. In that article you see that Nimur's position above is similar to that of Okun, but he is wrong, c = 1 can be interpreted literally without it having units as Duff points out. Count Iblis (talk) 01:37, 1 June 2012 (UTC)
Nimur is correct to point out that setting c = 1 is a very different thing from declaring that c = 1 light-second / second, but is wrong to imply that doing the former (common in certain fields of physics) is being sloppy with units. A general relativist, setting c = 1, is not equating temporal and spatial dimensions -- consider how they are handled differently in the metric tensor gμν = diag(-1,1,1,1) -- but is simply measuring them in the same units. -- ToE 22:30, 1 June 2012 (UTC)

Suppose I take a lump of mass m and convert it into "energy", specifically, some kind of light, i.e. a photon. Well, as light the mass m now has velocity c, the speed of light. So it has momentum mc. And the energy of the photon is then its momentum multiplied by the velocity c, putting you at mc2. I'm not quite sure how to make the second step as intuitively obvious as the first. Note from Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies that the kinetic energy of a fast-moving rigid body starts to shift from 1/2 mv2 toward 1 mc2 as it speeds up (see the Taylor series approximation) but "why" that is, in intuitive terms... hmmm. Wnt (talk) 04:59, 2 June 2012 (UTC)

Except that explanation is wrong because a photon has no rest mass. Even if it did, its momentum wouldn't be mass*velocity; it would have to be multiplied by the gamma factor to get relativistic momentum. -- (talk) 04:34, 3 June 2012 (UTC)
Rest mass is not always needed to calculate a particle's mass-energy or momentum though, thus Writ's observations are spot on. Quoting from our article on momentum:"The total energy E of a body is related to the relativistic momentum p by : where p denotes the magnitude of p. This relativistic energy-momentum relationship holds even for massless particles such as photons; by setting m0 = 0 it follows that:" Note that using the unit c=1 does not work well here, for the photon's momentum p, which it carries, and its energy E are dimensioned differently. Moreover, because of the mass-energy equivalence, we do have where . Modocc (talk) 01:57, 4 June 2012 (UTC)

Reaction rate data for iodine recombination[edit]

The only source of reaction rate data for the reaction I + I + M → I2 + M, where M = I2 that I could find is that given in the NIST database ( ), with gives:

A = 1.53; n = -5, and Ea = 0, for the arrhenious form k(T) = A Tn eEa/RT

Such a high value of n and low value of A seems very anomalous - n for this type of reaction is usually between 0 and -1, at least for elements in the P-Block of the periodic table. So I suspect it is in error. The trouble is, the reference given, Baulch, D.L.; Duxbury, J.; Grant, S.J.; Montague, D.C.; Title: Evaluated kinetic data for high temperature reactions. Volume 4 Homogeneous gas phase reactions of halogen- and cyanide- containing species (which is a book, not a journal as NIST states) is not available in any library I can access. Can anybody offer an alternate reference, or know where there is reliable data? I would like data for M = I too. Ratbone121.221.95.143 (talk) 08:23, 31 May 2012 (UTC)

Do we need to detox?[edit]

Do we accumulate toxins, that we need to get rid off? — Preceding unsigned comment added by OsmanRF34 (talkcontribs) 11:15, 31 May 2012 (UTC)

The human body has mechanisms to dispose of many naturally occurring toxins. However, depending on one's location, diet, etc., one may be exposed to high levels, or unusual kinds of toxins (e.g. due to water pollution). So there is no universal answer to the question. You could consult a doctor if you are concerned about a specific toxin. - Lindert (talk) 11:33, 31 May 2012 (UTC)
Indeed. Heavy metals are toxic and tend to accumulate. The most common problem is lead, which is ubiquitous in the environment due to decades of widespread use in paint, car batteries, gasolene, cable sheaths, all manner of things, even ladies' makeup. It appears that the body can get rid of lead, but the process is extremely slow, with a half life of many years. Wickwack58.167.248.70 (talk) 11:44, 31 May 2012 (UTC)
Actually the harmful lead in your body has a half-life of weeks. Only the lead in bone has a half-life of years, and that's generally not considered to be harmful. (talk) 21:23, 31 May 2012 (UTC)
I am not concerned with toxins in my body, but with detox diets and detox products. Do we need any of them? — Preceding unsigned comment added by OsmanRF34 (talkcontribs) 11:37, 31 May 2012 (UTC)
I think Detoxification (alternative medicine) covers this well enough, what more do you need to know? Since this is the science desk, the fact they are not supported by science should answer your question Nil Einne (talk) 11:49, 31 May 2012 (UTC)
(ec) Wikipedia cannot be relied upon for medical advice, but the whole "detox" thing is, frankly, not medicine. See Detoxification (alternative medicine). LukeSurl t c 11:50, 31 May 2012 (UTC)
The general rule about detox diets is "They are a lot of nonsense". If a toxin has accumulated, it is becasue the body has not evolved a way of effectively excreting or metabolising it. In many cases, certain metals being an example, a way for the body to deal with it is simply not metabolically/chemically possible. This means that nothing you can eat or not eat can overcome the problem. However, some naturapathy remedies may (or may not) cure a problem, and be referred to practitioners as "detox" while not actually a toxin eliminator. Wickwack58.167.248.70 (talk) 11:54, 31 May 2012 (UTC)
You can eat chelating agents that will remove lead from your system. They will generally also remove essential minerals from your system and make you quite ill. (talk) 21:26, 31 May 2012 (UTC)
Tim Minchin put it best. LukeSurl t c 11:58, 31 May 2012 (UTC)
This BBC story may be instructive; in it a scientist from the UK's Food Standards Agency explicitly calls detox diets "nonsense". I suppose if you consider money to be a toxin, these diets do seem very effective at purging you of that... -- Finlay McWalterTalk 13:16, 31 May 2012 (UTC)
But wouldn't be useful to eliminate, or try to eliminate, lead from our bodies? It tends naturally to bioaccumulate, and the amount of it in our diet and environment is increasing. Besides that, it doesn't seem to have any function in our organism. OsmanRF34 (talk) 14:14, 31 May 2012 (UTC)
Yes, it would indeed be useful. Unfortunately, being useful does not make it possible. Wickwack58.167.248.70 (talk) 14:58, 31 May 2012 (UTC)
It is possible, but the benefits do not outweight the side effects in all cases except acute lead poisoning. See chelation therapy. (talk) 22:28, 31 May 2012 (UTC)
There is doubt over whether chelation therapy works; it probably doesn't, and may even make the problem worse. See "Medical management of lead exposure", page 5, in Wickwack58.167.247.182 (talk) 02:14, 1 June 2012 (UTC)
Why do you think it probably doesn't work? That wasn't in your source. In fact, your source said "therapy...using metal-chelating strongly recommended for adults with acute lead poisoning". Also, I find it hard to reconcile chelation therapy not working with Harold McCluskey not dying from either radiation sickness or heavy metal poisoning. (talk) 04:51, 1 June 2012 (UTC)
On page 5, under the heading "Medical management of lead exposure", it says in the 3rd paragraph: "A large study of the effects of chelation therapy using DMSA in US children, aged 12 to 33 months with an average blood lead concentration of around 26 μg/dL, did not yield sustainable changes in blood lead concentration or improve cognitive abilities." So, yes it clearly is in the source. I'm not privy to what happened to Harold McCluskey, and the wiki article you pointed to has little or no value, because 1) the 1st reference given is an invalid link; 2) the 2nd reference given has absolutely nothing to do with Harold McC or what happened to him; and 3) he was exposed externally to Americium, an actinide with very different chemical properties to lead, a Group 14 element; 4) the link provided "for futher reading" only gives access to almost useless abstracts; and 5) I was talking about ingested lead. I shouldn't think much is known about the effects or treatment of Americium deposited on skin & clothing, but little absorption would be expected via skin. - it is possible anyway that his radiation count had dropped mainly due to discarding the contaminated clothing, and all the showers/baths etc he had over the time it took, noting that skin is continually replaced by the body, going from inside to outside & shedding. Wickwack121.215.60.29 (talk) 16:12, 2 June 2012 (UTC)
"the amount of it in our diet and environment is increasing" - this is completely false. Since leaded petrol and paint were phased out, the lead exposures of people in the developed world have dropped hugely. Obesity, smoking, and over-use of alcohol are the major external causes of ill health in the developed world, not lead. -- Finlay McWalterTalk 14:31, 31 May 2012 (UTC)
It is true that the amount of lead in the environment is not increasing. But it is also not true to assert that because lead has been eliminated from gasolene and paint then lead has ceased to be a problem. That's because a) lead in fuel was only one of several sources, and b) there's still a lot of lead-based house paint in situ, and people tend to sand it off and spread it around as part of refurbishment, dwellings are being constructed in former industrial areas contaminated with lead, and other reasons. Lead is a popular subject on Ref Desk, and a poster to a previous question cited a USA study that showed that US children have less lead now than in previous decades, but a sizable number are still over the US's arbitary and possibly rather high limit. In other countries, the picture isn't that good. I note that the USA has over several decades, had a much greater density of cars than other countries, and a greater percentage of light trucks was gasolene engines, making lead in gasolene more important. Here in Australia, children with lead over US limit gets reported in the media from time to time. It is true that lead, as generally found in body tissues, is not the obvious health impact of obesity, smoking, and excessive alcohol, but many authorities consider that lead has reduced the intelligence of the population slightly. Wickwack58.167.248.70 (talk) 15:29, 31 May 2012 (UTC)
I will post exactly what I posted last time; the idea that lead concentrations are not decreasing is absolute nonsense, and you are trying to invent doubt and controversy where none exists. Check these studies: (United States, further United States statistics, Australian study showing reduction since the mid-90s (page 5), albeit with smaller sample size, another Australian study showing significant reduction in over-exposure cases (page 13), the second half of that paper in case you were confused why it cut off in the middle). -RunningOnBrains(talk) 16:33, 31 May 2012 (UTC)
RunningOnBrians is not reading carefully before posting, and the links he's given do not refute what I said. I said lead is ubiquitous in the environment - the 2nd link he gave, an Australian Govt publication, says on page 2 "Despite removal of lead from petrol, lead is still ubiquitous in the environment and exposure continues." I have not said lead levels are not decreasing - I only said that despite remove lead from fuel and paint, the problem continues - a view which is supported by the links that RunningOBrains provided. RunningOnBrains has substantiated with linked references that there has been significant improvement in blood lead levels in the USA - which I have agreed with. But the USA is not the whole world, not even the whole developed world. In Australia, lead is mined or has been mined in several locations. As reported many many times in Australian media, what tends to happen is lead contamination occurs along the route and including the port city where the lead is transported for export. Every now and then the Authorities notice that children and animals are affected, and lean on the mining company to clean up their act, which (when they are being watched) they do. Then the Govt puts out a nice study showing the problem is fixed. Then it happens again. Mt Isa (refered to in one of ROB's links)and Esperance (refered to in one of my previous links: report are examples of this. The big picture is that in individual areas, lead contamination goes up and goes down. Over all, the problem continues. This is NOT to suggest that mining is Australia's biggest lead problem. Its just an example of part of the problem. Lead contamination comes from many sources, as ROB's links confirm, particularly page 2 in the second link. Wickwack58.167.247.182 (talk) 01:56, 1 June 2012 (UTC)
"RunningOnBrians"? So who's "not reading carefully before posting"? :) ←Baseball Bugs What's up, Doc? carrots→ 11:24, 1 June 2012 (UTC)
The first such dietary intervention I know of was by Aulus Cornelius Celsus, who wrote that "mallow or walnut juice rubbed up in wine" was an antidote for lead poisoning. [2] Apparently walnut [3] and Egyptian mallow [4] are fairly good at bioaccumulating lead, so I wouldn't entirely rule out the possibility of there being some sense to it, but there's certainly no modern evidence, and he didn't specify what compound might be involved. ;) Wnt (talk) 23:33, 31 May 2012 (UTC)
No, we do not need to detox in the same way as we need to breathe. It does have advantages, it may improve your health, but you're not required to detox. Only, if you've been exposed to something lethal, does it become neccessary. Just an idea. Plasmic Physics (talk) 23:52, 31 May 2012 (UTC)
Your idea is wrong Plasmic Physics. It does not have advantages, we are not getting contaminated by 'toxins', whatever that be, lead or not lead. (talk) 00:08, 1 June 2012 (UTC)
Could toxins (at low levels) actually have health benefits? Some damage done to the body that then gets repaired may make the body stronger... Count Iblis (talk) 02:03, 1 June 2012 (UTC)
Yes they could. See Hormesis. (talk) 04:57, 1 June 2012 (UTC)
What are you talking about? It does, and we could. Plasmic Physics (talk) 02:26, 1 June 2012 (UTC)
With all due respect, rubbish. It's highly commercial pseudoscience. HiLo48 (talk) 22:05, 1 June 2012 (UTC)
I have several points to add:
1) The assertion by the people selling these diets that everyone is full of unnamed "toxins" which need to be removed is utter quackery.
2) For those few individuals which really do have lead poisoning or some other overdose of a real "toxin", medical attention is required, not some silly diet.
3) That said, some of the diets aren't terrible, and an occasional day of fasting and/or drinking fruit juice might help you, not by removing "toxins", but by keeping you from downing your usual Wendy's Triple (bypass) with chili-cheese fries and a Double-Gulp from 7-Eleven. StuRat (talk) 04:56, 2 June 2012 (UTC)
I was a little confused by Stu's comment until I clicked on the link. Wendy's, a nationwide franchise in my country only sells icecream. Wickwack121.215.60.29 (talk) 16:38, 2 June 2012 (UTC)
It looks like the US Wendy's is about 25 times bigger, based on annual revenue, so Americans are the clear winner when it comes to obesity. :-) StuRat (talk) 18:23, 2 June 2012 (UTC)
Actually, everyone certainly is full of toxins needing to be removed - that's why we have kidneys and livers and P450 enzymes and all that good stuff. And many of those things are affected by diets - diuretics, cholecystagogues, compounds that increase or decrease the action of specific CYP450 proteins, etc. So the idea of a diet to remove toxins is anything but fanciful; the problem, of course, is that one would expect that over the course of evolution the body would have pretty well optimized its business of excretion. But ... there can still be deficiencies, and we're no longer living in the same environment or eating the same foods. So the idea is anything but quackery, but the implementation - that's another question! Wnt (talk) 19:38, 2 June 2012 (UTC)
We aren't "full" of toxins, as they are constantly removed. Thus, most people do not have their health adversely affected by "an accumulation of toxins", as they would have us believe to sell their crazy diets. StuRat (talk) 00:19, 4 June 2012 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── Our bodies have ways of dealing with the toxins we encounter on a daily basis. Individuals with renal failure must have regular dialysis to filter those toxins. Healthy adults don't need anything like these "cleansing" products, because said products don't actually remove anything your body can't handle. Anything that severe requires emergent treatment from an actual physician. And chelation for anything besides an acute, severe dose of heavy metals is a bad idea. As to deficiencies in diet, well, that's a completely separate issue. And again, one you should take up with an actual doctor: no generic diet is right for everyone, and you may need medication to deal with any kidney or liver problems. — The Hand That Feeds You:Bite 23:02, 2 June 2012 (UTC)

I'm curious about your use of the word "emergent". Did you mean "emergency" ? I've heard nurses in a hospital use it that way, which confused me. To me, "emergent" means "new", as in "AIDS was an emergent disease in the 1980's". StuRat (talk) 18:22, 3 June 2012 (UTC)

Which is More Buoyant?[edit]

Let's say I have two identical containers, each weighing zero. I fill the first one with a large amount of highly compressed air. The second one holds a vacuum.

Is it correct that the second one would be more buoyant than the first, because the air in the first weighs something, while the vacuum weighs zero?

Are there any other factors which would affect the buoyancy of either? Honeyman2010 (talk) 12:21, 31 May 2012 (UTC)

Yes, if the volume of the two containers is the same, the evacuated one and its (non)contents weigh less than the one with air. Immersed in some fluid (e.g. air or water) the evacuated one is more buoyant. Using this property to make a flying machine was proposed an impressively long time ago, as the vacuum airship. The hard thing is, of course, that in practice the pressure of the fluid surrounding a vacuum balloon will tend to crush it (and there's no pressure inside the evacuated vessel pushing back) - this reduces the volume of the container, so the airship doesn't fly. If you make the walls of the container strong enough to withstand the pressure (e.g. the 15 psi of air pressure) it has (now) to be made of something like steel - so the minor effective buoyancy of the vacuum is overwhelmed by the great weight of the steel vessel, and again the airship doesn't fly. That's why you've never seen a vacuum airship in the 350 years since it was proposed. Folks interested in the prospects of super-strong materials which may be made possible by nanotechnology think that some kind of diamond-fullerine-something stuff might be strong enough and light enough that it could hold its volume against air pressure and be so light that there would be a +ve net buoyancy. Theese "vacuum aerostats" are discussed a little in the novel The Diamond Age - but right now (as this is the science refdesk, not the science fiction refdesk) no material is (at least in a macroscopic scale) strong enough to do this, so vacuum aerostats don't exist. -- Finlay McWalterTalk 12:42, 31 May 2012 (UTC)
You can satisfy yourself that air has weight by a simple experiment with two balloons, (some sellotape), a stick, and some string. Take one piece of string and attach one end to the ceiling or similar, so that it hangs freely. Tie the other end of the string to the middle of the stick, adjusting to make it as equal as possible. Tie two shorter pieces of string, one to each end of the stick, again making it as balanced as possible. Blow up your balloons (stick a small piece of sellotape to each, to give a place to make a hole), tie their ends, use the strings on the ends of the stick to attach a balloon to each end. You now have a basic balance scale, which you should adjust until it is level. Once it is level, gently and carefully stick something sharp (like a needle) into one of the balloons (ideally into the sellotape) so that the air is released. As the air is released, that side of the balance should go up and the side that still has air should go down, showing that the air in the balloons has weight. (talk) 13:03, 31 May 2012 (UTC)
sorry, fallacious. the inflated balloon also has buoyancy that cancels its extra mass. I know, I tried it once. see Archimedes' principle. Robinh (talk) 09:04, 1 June 2012 (UTC)
The buoyancy does not completely cancel out the added mass since the air inside the balloon is under pressure. Whether the added mass minus buoyancy can actually be measured by a such a crude scale is another matter. Someguy1221 (talk) 09:34, 1 June 2012 (UTC)
This experiment may work as advertised but it's misleading to say that it measures the weight of air. That suggests that the scale is sensitive to air inside the balloon but not to air outside, which is completely wrong. The experiment works because the balloon is elastic and compresses the air. If you used a rigid container with a plunger instead, there would be no change on the scale as you pushed the air "out". -- BenRG (talk) 04:34, 3 June 2012 (UTC)

Transit of Mercury[edit]

There is an obvious problem with this article because there is a transit of Mercury in June 2012 and it is not listed. — Preceding unsigned comment added by (talk) 12:32, 31 May 2012 (UTC)

anybody can edit Wikipedia..... (talk) 12:35, 31 May 2012 (UTC)
Do you have a source? All sources that I can find say there is a transit of Venus, not Mercury. (talk) 12:36, 31 May 2012 (UTC)
Including Transit_of_planet_Venus — Preceding unsigned comment added by (talk) 12:37, 31 May 2012 (UTC)
The article is correct. It's consistent with NASA's list of past and future transits, which puts the next transit on May the 9th 2016, not 2012. -- Finlay McWalterTalk 13:01, 31 May 2012 (UTC)

Is Scientific Investigation Ever Irrelevant?[edit]

In a world of shrinking resources and growing poverty, is there a point at which scientific investigation becomes irrelevant, wasteful, and perhaps even immoral?

I love astronomy, cosmology, particle physics and more as much as any wannabe scientist. But I have trouble reconciling spending billions trying to find the Higgs boson while millions of our fellow human beings die every year from starvation and disease. Aside from generating Nobel Prizes, and providing a good living for a relatively tiny population of scientists, achievements such as finding the Higgs, or dark matter, or catching neutrinos or a million other such quests will not improve the life of anyone alive today or perhaps for many coming generations.

Shouldn't science encourage it's best and brightest minds to solve the fundamental problems of this world before tackling issues such as the shape of the Big Bang?Honeyman2010 (talk) 13:08, 31 May 2012 (UTC)

Yes, we should abandon ALL other human endeavors, including any money for the Olympics or Arts, or any scientific or educational enterprise that is not fully directed to increasing crop yields. When EACH and EVERY mouth is filled, only then can we morally go on to fund other things. The reality is that human experience is heterogeneous, and we are designed to be interested in and strive forward in many fields at the same time. I for one think there is more to human progress than catering for those who have one hand scratching their bums, and the other pointing down a throat leading into an inexhaustible gullet. Myles325a (talk) 08:01, 4 June 2012 (UTC)
This is a common criticism of science funding but its validity ultimately hinges on being short-sighted. Only a narrow construct of "solv[ing] the fundamental problems of this world" includes only the adequate near-term production and distribution of food and medical supplies. Particle physics and other esoteric fields may not "solve the fundamental problems of this world" today, but the research findings may solve the future fundamental problems of this world. If there's one thing the history of science tells us it's that one cannot reliably predict the future value of basic science advances, but in aggregate it's typically a huge long-term payoff. — Scientizzle 13:20, 31 May 2012 (UTC)
(ec) Science is often driven by curiosity. Newton and Einstein did not have immediate economically profitable applications for their theories. It is impossible to know what amazing technologies will be made possible by fundamental research. It's like exploring unknown lands: You don't know what you will find, or what setbacks you will suffer. The expedition is expensive and you don't know if you'll ever earn it back. And yet without such curious people, we would not have many of the things we have. - Lindert (talk) 13:21, 31 May 2012 (UTC)
(WP:EC):Should we encourage scientists to study humanitarian problems? Sure, and we do. But that doesn't mean we can't also study other things. Part of why we value basic science is that we don't know what may or may not be useful in the future. Hardy is often quoted as saying "No one has yet discovered any warlike purpose to be served by the theory of numbers or relativity, and it seems very unlikely that anyone will do so for many years." In a sense, he was proud of the abstraction of his work, and if it didn't "do good", at least it would not be "bad", e.g. serve as a weapon. Of course, he was wrong. The theory of relativity is used in 'many' areas today, e.g. satellites and GPS. While these can be used as weapons, they also have saved many lives. Likewise, Hardy's number theory laid the foundation for modern cryptography, which is a similarly multi-use tool that can be used both to harm people and to help them. SemanticMantis (talk) 01:15, 1 June 2012 (UTC)
Wasn't the Manhattan Project based on relativistic science? And Robert McNamara certainly though there was a warlike application for number theory. (talk) 21:02, 31 May 2012 (UTC)
On the Manhattan Project: not really. Nuclear fission is non-relativistic. You can use E=mc^2 as a shorthand for calculating the energy release per fission, but you can also do it classically as the repulsion of two positive masses (the energy is mostly kinetic). Relativity didn't play a big role in the Manhattan Project, though it does help understand some of the fundamental behaviors. Quantum theory was more important. --Mr.98 (talk) 00:33, 1 June 2012 (UTC)
I said "Of course, he was wrong" -- meaning that relativity and cryptography have been used for warlike purposes, even thought Hardy thought they wouldn't be in his near-future. (They have also been used for "good" purposes, as I alluded). SemanticMantis (talk) 01:15, 1 June 2012 (UTC)
I know. I was just pointing out how wrong he was...and conversely how right you were :). (talk) 05:52, 1 June 2012 (UTC)
  • Lastly, changing what is studied comes down to scientific funding. There is no "science" that can "encourage" people to study a topic, there is only either funding available, or not. There are many politicians who campaign for less governmental science funding, and try to mock "useless" science being done today. Usually these same politicians also favor large defense spending, and don't mention humanitarian goals at all. So really, while there is a culture of science (or several cultures of several sciences), it's the power of the purse that ultimately determines what research gets done. (I'll let someone else cover how private/corporate funding of research effects what topics are studied;) SemanticMantis (talk) 13:28, 31 May 2012 (UTC)
Any time you start to think that too much is spent on science, just take a look at how much is spent on war. Science isn't the first place I'd start cutting. The NASA budget is $18 billion; the budget for the entire Department of Energy (which includes managing the nuclear stockpile aside from funding particle physics, etc.), is $30 billion. The entire National Science Foundation, which supports a vast array of basic university research, has a budget of $7 billion. The 2013 budget request for the Department of Defense is over $600 billion, and that's down from almost $700 billion in 2011. The Large Hadron Collider will cost something like $10 billion total, which is well under a billion a year for its construction. --Mr.98 (talk) 13:33, 31 May 2012 (UTC)
That's a fallacy. The Department of Defense also produces science. And without defense, you won't have any means to produce any science. OsmanRF34 (talk) 16:33, 31 May 2012 (UTC)
The DOD does spend about $70 billion for testing and developing new weapons systems (which involves some science but it's pretty narrow), and maybe $12 billion on more basic research. So that's not nothing, but it still means that about 90% of that spending is towards non-science. And the fallacy here is implying that cuts in the DOD budget would somehow mean you'd be "defense-less" in a way that would destroy the means to produce science. The vast majority of the current DOD budget is going towards fighting wars with countries or groups that in no way imperil US science. --Mr.98 (talk) 00:33, 1 June 2012 (UTC)
Historical segue: in the 1940s, in the middle of World War II, US policymakers were having just this discussion. Should science be funded with public funds, and if so, who should decide how those funds are distributed? Should they be applied to specific ends, or should they be also given out towards basic knowledge? A bill was introduced that would basically make a US science agency that would only work on applied research. Vannevar Bush opposed this, and connived FDR into letting him do a report on it, which became Science—The Endless Frontier, one of the classic defenses of basic research. Bush thought you had to let scientists dole out the money and that application couldn't be the reason for it; focused and applied research might work in places where you really knew what the outcome was supposed to be (e.g. the atomic bomb and radar, both of whom Bush were involved with), but it didn't guarantee you'd find unexpected things. The other problem with applied research is that you end up warping the science to fit the application — so we know a lot about any science plausibly related to military applications of the ocean, for example, but a whole lot less about things that aren't interesting to the military. You quickly end up with a somewhat "closed cycle" of knowledge that only feeds familiar, old problems.
Bush's scheme didn't totally play off but something similar was eventually created in 1950 as the National Science Foundation. To say the NSF is only about basic science isn't exactly right — they are supposed to give a lot of lip service to things with tangible benefits — but it's as close to that sort of thing as we have in the US. (All of this is described in brief [[5]].) --Mr.98 (talk) 13:52, 31 May 2012 (UTC)
We don't live in a world of growing poverty. That is simply untrue. Poverty has declined enormously in recent decades. You can see some statistics on this World Bank website. --Tango (talk) 15:29, 31 May 2012 (UTC)
Scientific progress is just about impossible to predict. I would guess that in the early 19th century, studying electricity must have seemed to many like an esoteric and pointless pursuit, yet within a few decades it led to all kinds of hugely important applications. (talk) 16:00, 31 May 2012 (UTC)
You wouldn't know it from the mass media, but particle physics has actually seen a great drop-off in activity over the last few decades. The funding levels have gone way down, and I personally know a number of brilliant physicists who have migrated into other fields, including my own field of neuroscience. Looie496 (talk) 17:39, 31 May 2012 (UTC)
There's something very strange about the notion that basic research is important because some of it turns out to have applications—as though if we had the benefit of hindsight we would only want to do the parts with applications and not bother with the rest. Science itself is something that people want to do. It is its own point. You say that you love cosmology and particle physics. So do I. Their continued existence improves our quality of life, even if they never lead to improved ways of fueling and maintaining our 100-watt biological heat engines. -- BenRG (talk) 17:45, 31 May 2012 (UTC)
I agree, there is something strange about that argument. But it is a well-known argument that can be used to successfully defend the value of science to a more Utilitarian crowd. I also agree that certain fields like cosmology are, to some extent, "their own point". However, that is also weird, because it verges on equating certain types of science with certain types of art... which is an interesting discussion to have, but perhaps too subtle and nuanced for this venue. Basically, the discussion becomes no longer a topic for science per se, and instead a subject for philosophy (of science). SemanticMantis (talk) 18:09, 31 May 2012 (UTC)
"A more utilitarian crowd"—I argued that basic science is justified by the happiness it directly creates. I don't see how you can get more utilitarian than that. I think you mean a crowd of people who don't enjoy science. I'm not sure what those people do enjoy, but I'm pretty sure it's not art, since "basic art" gets even less funding than basic science. -- BenRG (talk) 20:33, 31 May 2012 (UTC)
I think the OP was assuming that you get some enjoyment out of knowning the results of some expensive scientific experiments, but he's just saying it's not the most utility you could be getting for your purchasing power. If you could chose between spending a billion dollars on food for the poor or a new particle accelerator, the food might give 1/10000 of the world's population a massive boost in their quality of life, whereas the accelerator might make 1/2 of the world's population experience a tiny joy and say "wow". (talk) 21:14, 31 May 2012 (UTC)
I have trouble reconciling spending billions on popular music while millions of our fellow human beings die every year from starvation and disease.
Why don't you download it for free? — Preceding unsigned comment added by OsmanRF34 (talkcontribs) 18:09, 31 May 2012 (UTC)
Why exactly do you waste your money on internet access and electricity and buying a computer when that money could go towards feeding starving children in Africa? Certainly you do not need any of these things to survive. -RunningOnBrains(talk) 21:11, 31 May 2012 (UTC)
  • Insofar as human beings have any purpose beyond turning food into shit, one of those purposes should be expanding the collective knowledge of humanity. In that way, all basic science reseach is highly relevent, indeed I can think of no more relevent human than the expansion of collective knowledge. Everything else we do is turning food into shit. Every other form of life does that t0o. What makes us human is our ability to acquire and store knowledge as a species. If you take that away, you give up your humanity. --Jayron32 18:23, 31 May 2012 (UTC)
Imagine in the late 19th century, if the scientific community in general decided that the study of aeronautics was unnecessary. "Of what use is it for people to fly through the air? There are plenty of problems on the ground."    → Michael J    20:49, 31 May 2012 (UTC)
The sad part is that most economists know how to eliminate most poverty and ameliorate almost all of the rest, by returning to the high effective corporate tax rates of more prosperous times which would cause companies to invest in labor and production, creating consumer demand and growth, instead of paying the less risky small tax to bank their record profits, which leads to stagnation and widespread unemployment.
The problem is that raising corporate taxes is politically unpalatable to those with the most money (corporate officers) so with their powerful lobby virtually nobody knows about the macroeconomic effect of all corporations facing the same decision to either spend to hire and produce or bank profits. But it's the whole reason companies are charged "income" taxes on profits instead of receipts, so they can dodge taxes by growing, and it's how the U.S. paid off the World War II debt, which was three times today's relative to GDP -- by growing instead of running a surplus.
The way to solve this is to institute a mandatory corporate fiduciary duty to seek prosperous economic conditions, including advocacy of effective corporate income tax rates which make hoarding profits idle cost more than labor, production, and growth. How do we achieve that? I'll ask on the Humanities Desk. (talk) 00:22, 1 June 2012 (UTC)
Interesting graphs, thanks. I think many of us agree that the issues brought up in this question--money and time spent on basic research as opposed to humanitarian goals -- are more governmental and philosophical in nature than scientific. SemanticMantis (talk) 01:15, 1 June 2012 (UTC)
  • All we have to do is wait for the results of the British research impact measure…Fifelfoo (talk) 00:43, 1 June 2012 (UTC)
but surely you can all agree that as the dollars dwindle less and less of them will go toward funding wacky futuristic pursuits and more will go toward, let's for the day. Until the last dollar is spent entirely on food, etc. As the old native American proverb goes, only after the last fish has been caught will you realize that money cannot be eaten. As for the corporate tax discussion there is a delicate balance between taxing and having the corporation stay domesticated. If you tax them too much they can pickup and expatriate to another country. (talk) 12:15, 1 June 2012 (UTC)

The problems we face are actually caused by us consuming too much, and as a result the economic output being diverted to produce useless and wasteful stuff. Spending a lot more on science would be a net benefit to society, even if none of the results are of any use. Count Iblis (talk) 17:02, 3 June 2012 (UTC)

HAHA, Count, then burn or send all your money to me to help start solving the problems! (talk) 13:30, 4 June 2012 (UTC)

Neutron Spin[edit]

What are the physical characteristics of a neutron which enable us to determine it has spin? — Preceding unsigned comment added by (talk) 16:09, 31 May 2012 (UTC)

One thing that comes to mind is that neutron diffraction techniques allow the determination of magnetic ordering structure in a solid, because the spin on the neutrons interacts with the magnetic moments in the structure of the solid, whereas x-ray diffraction uses photons (which have no spin) and doesn't provide magnetic information. Brammers (talk/c) 16:58, 31 May 2012 (UTC)
Photons do have spin, actually. --Trovatore (talk) 20:50, 31 May 2012 (UTC)
Oops, apologies. So for those who are a bit hard of thinking tonight, how come the photon's spin doesn't result in magnetic peaks in x-ray diffraction patterns? Brammers (talk/c) 22:03, 31 May 2012 (UTC)
That's out of my depth, I'm afraid. I might speculate that it's because neutrons do have nonzero magnetic moment (presumably because it's made up of charged quarks, even though its overall charge is zero), whereas I think the magnetic moment of a photon is zero (but I'm not sure of that). --Trovatore (talk) 22:37, 31 May 2012 (UTC)
Our article, Spin (physics) has a section "Spin vector" which briefly describes particle-spin-detection methods. -RunningOnBrains(talk) 21:07, 31 May 2012 (UTC)
Nuclear magnetic resonance#Nuclear spin and magnets has a nice discussion of an effect of neutron spin. The result is that NMR susceptibility is isotope-specific, not element-specific. DMacks (talk) 04:31, 1 June 2012 (UTC)

How many fingers does a hand need?[edit]

So I was just playing Dungeon Siege III and in it, a goblin asks "How many fingers does a hand really need?" and it got me thinking. If you were to make a robot with hands, what is the minimum amount of digits it would require in order to do all of the physical tasks that humans are capable of? ScienceApe (talk) 20:26, 31 May 2012 (UTC)

Five. Consider one physical task that humans are capable of, that of holding four playing cards one each between the fingers. Stating your requirements in other ways would reduce the number of digits needed to three (ability to manipulate an object whilst always gripping it with two digits) or two (finger opposed to thumb enabling power and precision grips). Of course, if you want to redefine the digit sufficiently (make it very long and having a very great many degrees of freedom), you could get away with a single digit. --Tagishsimon (talk) 20:36, 31 May 2012 (UTC)
"need" is pretty dependent on purpose, as Tagishsimon demonstrates above. For a discussion about why hands are the way they are, see the hand article, specially the section on evolution. (talk) 22:25, 31 May 2012 (UTC)
Depends on how much functionality you like in a hand. It's pretty easy to get an idea of what sorts of tasks you can do with two fingers, three, etc. Typing and the playing of musical instruments are two things that would likely be drastically affected by the number of fingers a theoretical person may have; of course, Steve Vai and Django Reinhardt would have two completely different answers to this question... Evanh2008 (talk|contribs) 22:30, 31 May 2012 (UTC)
Russ Conway was an example of a musician who was successful with fewer than the normal number of fingers. --ColinFine (talk) 23:52, 31 May 2012 (UTC)
I once saw a man with two fingers playing blues guitar (quite well) on Market Street, San Francisco. He held a pick in his remaining fingers and tuned with his stump. —Tamfang (talk) 18:31, 2 June 2012 (UTC)
OR: I'd go with three, two fingers and a thumb. Two would only give you stability along one axis, while more that three doesn't significantly improve things, at least not the way the human hand is laid out. As an added bonus, you could still give someone a recognizable finger. Clarityfiend (talk) 00:05, 1 June 2012 (UTC)
The original question was about robot manipulators. Some of the most powerful lifters I've ever seen are vacuum lifters - non-gripping armature attachments that use pneumatic pressure, rather than gripping contact force, to lift objects. Robots have all sorts of design-decision freedoms that biological systems do not. You can design a robot with zero or n fingers, or magnetic fingers, or sticky glue on their fingers; ... Here's a fantastic video of my former professor, lecturing on robot manipulator kinematics, and a transcript of the graduate-level material on robot armatures. The video shows many interesting robot armature manipulators and discusses how robot engineers model their physical capabilities theoretically, and translate those physics into computer program code. Nearly the full course is available online at Stanford Engineering Everywhere's "Artificial Intelligence - Intro to Robotics page. If I recall, lectures 4, 15, and 16 have extensive discussions about "finger"-like robots, and of course we worked on the Barrett WAM whole-arm manipulator robot in the more advanced experimental section (which is harder to post online!). Needless to say, it is much more difficult to program a robot with n extra fingers; simplistic robot manipulators use one-dimensional (one- or two-finger) grapplers or actuators. Nimur (talk) 00:25, 1 June 2012 (UTC)
Another robot interesting gripper that doesn't use fingers is this balloon filled with coffee grounds [6]. It uses suction to lock the balloon into a shape that grips via contact forces. SemanticMantis (talk) 02:00, 1 June 2012 (UTC)
A full set of fingers is useful when swimming. Alansplodge (talk) 17:18, 1 June 2012 (UTC)
Members of the pinniped family - "(from Latin pinna, wing or fin, and ped-, foot)" - seem to counter-indicate that assertion! They've convergently evolved toward a fin-like appendage; and though their limbs have similar anatomical structures to our fingers, they're not really useful for gripping. We have a whole article on this from the biological point of view: on opposition and apposition of fingers. Nimur (talk) 18:32, 1 June 2012 (UTC)
Well, their finger-bones (phalanges) are inside the fins aren't they? I reckon that they still need to have them all. Alansplodge (talk) 01:04, 2 June 2012 (UTC)
Do they still have five sets of tendons? —Tamfang (talk) 18:33, 2 June 2012 (UTC)
A friend of mine has only 3 fingers on his left hand (including the thumb). He can't think of anything he can't do with his left hand that his right hand would be capable of. So 3 is sufficient. (most characters in comics do fine with 4 fingers btw) Joepnl (talk) 01:27, 2 June 2012 (UTC)
(Ok, chopsticks won't work in his left hand)Joepnl (talk) 01:29, 2 June 2012 (UTC)
Eh? I use exactly three fingers for chopsticks. —Tamfang (talk) 18:16, 2 June 2012 (UTC)

See Yubitsume. Each finger that is lost significantly reduces one's ability to hold a sword tightly. Unique Ubiquitous (talk) 01:36, 2 June 2012 (UTC)

New York City cab drivers really only need 1 finger. :-) StuRat (talk) 04:40, 2 June 2012 (UTC)
Having worked as an auto mechanic and an electronics technician, I can say that for many tasks, less fingers are not a problem (like Joepnl, I know friends who have each lost a finger in accidents, but they don't seem to be abnormally limitted in what they do), but 3 arms would be good. A 3-arm person or robot could do many tasks that currently require two, or could do without clamps. Sometimes, you need both arms/hands to hold tools, and your mate to hold the part(s). Wickwack121.215.60.29 (talk) 14:37, 2 June 2012 (UTC)
If you had three arms, you'd find that some tasks need four. —Tamfang (talk) 18:16, 2 June 2012 (UTC)
Dilbert cartoons pointed out that the computer seems to be designed for 3 hands, one to operate the mouse, and two for the keyboard. StuRat (talk) 18:15, 3 June 2012 (UTC)