Wikipedia:Reference desk/Archives/Science/2008 May 6

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[edit] May 6

[edit] Dino-mite question

What are the 10 newest dinosaurs? --DinoDude08 (talk) 00:33, 6 May 2008 (UTC)

What do you mean by "newest"? Most recently discovered, or most recently lived? --Tango (talk) 00:36, 6 May 2008 (UTC)
General Motors, Ford, and Chrysler are starting to look like really good contenders for at least three of the ten positions.
Atlant (talk) 13:14, 6 May 2008 (UTC)
i think it's safe to say that Dinodude meant newest discovered.... but that can be a tricky question since paleontologists are reclassifying old bones all the time... added to that the debate that sometimes occurs when "new" dinosaurs emerge, which is actually a lot more often than you might think. you just want what the latest news in paleontology is, check out [www.palass.org this], or this. -ΖαππερΝαππερ BabelAlexandria 20:49, 6 May 2008 (UTC)
Ok. Dino Dude joking aside. Currently birds are believed to have evolved from dinosaurs. So, as our article says "they are the only living dinosaurs". Have a look at the Hoatzin which seems to have regained some dinosaur traits. (Claws on their wings.) Non-bird dinosaurs are usually thought to all have perished in the K-T extinction. So singling out 10 species would be rather arbitrary. There are occasionally bones found above that layer, but scientists think that's because they were moved later. As far as recent discoveries are concerned, it can take a very long time from the moment the bones are dug up, to the point when the bones have been prepared, to the identification of the species and finally the announcement. Look at Xenoposeidon for example. Since it is much more common that only one or two bones remain, rather than an entire specimen, scientists are very careful before they announce a new species. It is not uncommon, though, for bones to get relabeled to belong to a different species than the one originally identified. A quick search resulted in following other candidates for a "top ten" list, but please don't view this as correct and complete:
Paluxysaurus, Eocarcharia dinops, Kryptops palaios, Rugops primus, Velafrons, Nemicolopterus crypticus, Albertaceratops nesmoi, Gigantoraptor erlianensis, Mei (dinosaur), Onychonycteris was a bat and may not qualify
There was mention of a recent find in China, but I could not get at the information. Hope this helps. Lisa4edit71.236.23.111 (talk) 23:19, 6 May 2008 (UTC)

[edit] About NARCOTICS:

About NARCOTICS: I wanted to know can anyone help me find out all the slangs and everything there is to know about illegal narcotics from herb to cocaine, soft to hard, numbers, everything?? —Preceding unsigned comment added by KTTK2008 (talk • contribs) 00:39, 6 May 2008 (UTC)

What you want is www.erowid.org. Trust me, they have everything on every drug you can imagine, from caffeine to LSD. Chemistry, law, effects, even experience reports. Have (safe) fun. --Shaggorama (talk) 09:56, 8 May 2008 (UTC)

[edit] Genetic code

Do I understand correctly that if I have genes, which represent a high probability of my contracting a certain ailment that an insurance company can not use that information to deny insurance to me or as the basis for increasing my insurance premium? --Schaum 01:29, 6 May 2008 (UTC)

This is bordering on legal advice, which we are not really qualified to dispense. I suggest asking your/a lawyer. Wisdom89 (T / C) 01:30, 6 May 2008 (UTC)

Nonsense. --Schaum 10:52, 6 May 2008 (UTC)

In most places, the insurance company can use such information freely to jack up your rates. It's only in the very rare jurisdiction where a law has been passed to prevent this that they have to think twice about doing it. - Nunh-huh 01:41, 6 May 2008 (UTC)

If you're in the US, see Genetic Information Nondiscrimination Act. However, be aware that (1) that link is only to a Wikipedia article, which could be misleading, (2) the act has not yet been signed into law, and (3) we don't yet know how effective it will really be in meeting its intended purposes. --Anonymous, 04:44 UTC, May 6, 2008.

When I first learned about actuary tables I recall that insurance companies included anything they could correlate. In fact I learned that is what made insurance possible. Consequently I do not see them doing otherwise under any circumstance short of pulling their license to do business which would require a law that I am sure they will be sure is never passed. --Schaum 10:52, 6 May 2008 (UTC)
I agree. I also hope, though, that within the next few years we'll have (in the United States, anyway) turned health coverage into a public service (like police and fire coverage) and so these sorts of things will be moot concerns. I understand that those in a for-profit business need to make money, but I think it's stupid to have healthcare be a for-profit business in the first place. --98.217.8.46 (talk) 12:26, 6 May 2008 (UTC)
98.217.8.46 i'd read a bit more about public-provided health insurance schemes before deciding it is foolish to have for-profit provisions of healthcare. Most of the developed world have for-profit provisions of water, energy supplies and food-stuffs (all essential to supporting life) without major concerns. Drug research is also for-profit and is potentially the reason for such innovation (though patent/copyright law also potentially cause slow down of development). I recommend the chapter on healthcare from the book 'The Undercover Economist' - it mentions a very interesting health-system. I forget which country it is, but i think it is Sri Lanka or somewhere in the orient which had one that, for me, made the most sense (a somewhat hybrid of government, individual and insurance provision) —Preceding unsigned comment added by 194.221.133.226 (talk) 14:38, 6 May 2008 (UTC)
I've read into it—I think more people benefit from easy, affordable basic care than do, on the whole, from all of the supposed research and drug production that the money is paying for (and I think the costs of the privatized healthcare are far too high, both economically and from a human point of view). (And the economics of water, energy, and foodstuffs are highly regulated in most countries, though they have a superficial appearance of a free market on the client side of things.) Anyway, that's a different question, and a debate at that. We can stop this here. --98.217.8.46 (talk) 03:27, 7 May 2008 (UTC)

[edit] Washingtonion Palm trees

I have read the Wikipedia essays on Palm Trees but cannot find an answer to the following question: What is the life expectancy of Washingtonian Fillifera, Washingtonian Robusta and Medjuel date palms? Particulaly in the southern California area. Thanks, WSC —Preceding unsigned comment added by 75.85.203.191 (talk) 02:17, 6 May 2008 (UTC)

I'm not sure about date palms (Phoenix dactylifera), but Washingtonia filifera (California Fan Palms) and Washingtonia robusta (Mexican Fan Palms) can easily get to be 100 years old. There are numerous plantings of these palms in southern and central California that date from the early 20th century. I suspect that they can live much longer than that if in the right environment. W. filifera is, of course, native to the desert in southern California.--Eriastrum (talk) 15:37, 6 May 2008 (UTC)

[edit] Alaskan Mosquitos

How do Alaskan Mosquitos survive the winter? Do they fly south before winter? Do they hibenate? 203.94.145.126 (talk) 04:42, 6 May 2008 (UTC)

Mostly the mosquito eggs laid at the end of summer just wait to develop until it gets warm again. Dragons flight (talk) 04:57, 6 May 2008 (UTC)
They carry off bears to feed on during the winter.
Seriously, Dragons flight has it right. The eggs survive the winter and hatch again in spring. The adults simply die off. Which is a good thing. Those suckers are huge. There's a reason Alaskans call them the "state bird." -- Kesh (talk) 20:57, 6 May 2008 (UTC)

[edit] plastic containers

Before throwing a large number of various plastic food product containers in the trash where can I find information about personal methods of recycling such as using soda bottles as seedling starters, etc.? --Schaum 06:23, 6 May 2008 (UTC)

Okay then, where best to ask this green question, if not the Wikipedia reference desk? 71.100.14.205 (talk) 01:12, 7 May 2008 (UTC)
Most councils or government agencies will offer recycling tips. Check out these, for starters: [1], [2] [3], [4] and so on (try googling). http://www.recyclethis.co.uk/ looks good, at first glance. But remember that not all plastics are suitable for reuse. Gwinva (talk) 01:27, 7 May 2008 (UTC)

[edit] IMAX type 3D Camera doing time lapse photography!!??

OK, did I think of this first? Beautiful films of plants growing in time lapse AND 3D!!

Know what I'd really like to see? In Australia, after one of our bushfires, the whole scene looks like a blackened hell hole. Then in the space of several months, it regenerates. Oz bush is DESIGNED to burn and regrow. And no one has EVER filmed it in time lapse. It would look so coooool. National Geographic, where are you? And I would like a credit on your film. And some money. Myles325a (talk) 08:06, 6 May 2008 (UTC)

How do you know no one has filmed it with time lapse photography before? Also you don't a special camera special camera to do 3D photography just 2 identical cameras set at a fixed distance apart, see Stereoscopy Nil Einne (talk) 15:41, 6 May 2008 (UTC)

[edit] The size of the atom according to the ancient atomists

I've posed this question here as well, from WP:RD/H, in case anyone can give further scientific insight. PeterSymonds | talk 10:26, 6 May 2008 (UTC)

From this article, [5] I got this quote:

Some controversy surrounds the properties of the atoms. They vary in size: one report—which some scholars question—suggests that atoms could, in principle, be as large as a cosmos, although at least in this cosmos they all seem to be too small to perceive

Can anyone tell me more? Who was it who suggested atoms could be so huge? Were they suggesting another universe populated with a single gigantic atom?

Thanks Adambrowne666 (talk) 10:23, 6 May 2008 (UTC)

I can't find that quote in that article. Without context, it's difficult to work out what it means. It seems to be a philosophical article, which would suggest it doesn't really mean much at all. --Tango (talk) 13:35, 6 May 2008 (UTC)


Sorry, Tango, you're right; it was the wrong link - I've fixed it now.Adambrowne666 (talk) 21:18, 6 May 2008 (UTC)
Ok, even with context I have no idea what it's talking about. It does provide a reference, though - see if you can find a copy of "Diels, H. and W. Kranz, 1951, Die Fragmente der Vorsokratiker, 6th ed. (Berlin)." and find "68A47" in it (I'm not sure what that means, chapter and page, or something, maybe). Of course, it looks like it's in German, so if you don't speak German you will need to find a translation... --Tango (talk) 23:47, 6 May 2008 (UTC)
This sounds remarkably similar to a theory i've heard of which says the universe is contained within a quark? Regards, CycloneNimrodTalk? 17:10, 6 May 2008 (UTC)
Keep this in context. Thomas Kuhn showed that often the meaning of a scientific term changes after a paradigm shift in a way not perceived by the proponents of the new paradigm. Our notion of the atom is almost certainly incomensurable with what the ancient greeks meant; atomic theory as we know it today didn't really start to develop until the time of the alchemists, and what we believe now has been so drastically affected by quantum mechanics it would be incomprehensible that if you and democritus (or even if you and an alchemist) had a conversation about atoms that the two of you would be talking about the same thing. --Shaggorama (talk) 10:05, 8 May 2008 (UTC)

Thanks, everyone Adambrowne666 (talk) 23:20, 10 May 2008 (UTC)

[edit] Re: Pronator quadratus muscle

Why the contraction of pronator quadratus produces pronation, and not supination? Think of it, unlike pronator teres, it is not attached to a more proximal fixed point like the medial border of the humerus. This muscle runs absolutely perpendicular to the radius and the ulna.

I have thought about it, and feel that when the forearm is supine, there's no further margin for supination, so the muscle acts to bring the radius closer to the ulna, and not vice versa. And, when the forearm is pronated fully, the muscle must be getting so much relaxed (consequently, also shortened) that its contraction cannot further shorten the fibers, hence no movement occurs in this position.

Well, this is just a guess. It'd be nice if someone approves of it, or corrects my ideas. Regards.

PS: I have posted the same doubt on the talk page of the above article. Didn't get any response. Any way, it's not a "high profile" muscle ;). So, that's understandable.

Ketan Panchal, MBBS (talk) 17:48, 6 May 2008 (UTC)

Pronator quadratus runs from the lateral (outside) of the radius to the medial border of the ulna, and is found in the anterior compartment of the forearm. Thus when the arm is in a supine (palm up) position, contraction of pronator quadratus acts to roll the outside of the radius toward the ulna, which is pronation. It may help to visualize this by placing your right forearm palm up in front of you and then pinching your ulna and radius with the index finger (on the radius) and thumb (on the ulna) of your left hand. The pinching will simulate contraction of pronator quadratus, and will show the action of the muscle. -- Flyguy649 talk 06:01, 7 May 2008 (UTC)

[edit] The Law of Gravity

I was in science class yesterday doing a chapter on gravity. I asked the teacher whether or not gravity was a law and my teacher said that gravity was only a theory. This sparked a classwide debate, which resulted in my getting a detention for "disrupting class." My teacher will refuse to explain why gravity is a "theory." I think that gravity is a quite obviously a law. I need to know: am I correct? Could someone help me? Thanks. 31306D696E6E69636B6D (talk) 18:01, 6 May 2008 (UTC)

Newton's law of universal gravitation can be proved mathematically and is an accpeted physical law See responses below. However most of science is just accepted theory based on "what works". If you look through the history of science, theories and laws have constantly been debated and adapted using both mathematical and experimental evidence. Sorry about the detention. I really don't see how sparking a debate can be a valid reason for a detention unless it was during a test or something. Tbo 157(talk) 18:11, 6 May 2008 (UTC)
What do you mean when you say it "can be proved mathematically"? It's not even a correct model of reality—hence the formulation of general relativity. In response to the question, the distinction between a scientific law and a scientific theory is essentially meaningless, and often based on historical use. We talk about the "law of universal gravitation" and the "theory of relativity", even though the latter is certainly more correct than the former. If your teacher really said "only a theory", I would criticize that use—"theory" is quite a strong word in science, and is only used when the evidence is very strong. It doesn't mean "guess" or "hunch" like it might in everyday use. -- Coneslayer (talk) 18:22, 6 May 2008 (UTC)
  • (edit conflict) Indeed, the first response is wrong. Not only is Newton's law of universal gravitation not proven, it is, on the contrary, disproven and has been replaced by Einstein's General Theory of Relativity, which is a better description of reality, but also quite likely wrong. Strict proof is only possible in mathematics. In science, a theory is a self-consistent explanation of a set of observations that allows testable predictions. A "law" is a concise statement of (usually cental parts of) a theory that has been very successful in making correct predictions. Newton's theory, while certainly wrong, is a good enough approximation to be still very useful, so we still talk about the "Newton's law of gravity". In fact, a good theory is the best you can hope for in science. And, while I'm nitpicking anyways: Gravity is neither a law nor a theory, but rather a force ;-) --Stephan Schulz (talk) 18:31, 6 May 2008 (UTC)
Well, Newton did prove the law of gravitation mathematically - but only after taking Kepler's laws of cosmic motion and his own law's of motion as postulates. The great step forward Newton made was to show that both terrestial and celestial motion could be described by a common set of laws. All scientific theories have to start with something, ad what you can prove mathematically depends on what the "givens" are that you are assumming. We constantly modify the "givens" in the light of scientific experiments. We constantly try and reduce the number of givens we have to assume but we will never eliminate them entirely, there will always be at least one law that must be accepted without proof and from which everything else is derived. SpinningSpark 18:38, 6 May 2008 (UTC)
There's a common misunderstanding about what the word "theory" means. A theory is stronger than a law. A law is what you get when you do lots of experiments, plot them on a graph and draw a trendline - the formula for the trendline is the law. A theory is something which explains why that law holds, and allows you to predict more laws. "Only a theory" is nonsense, since a theory is the strongest thing you have in science. --Tango (talk) 18:29, 6 May 2008 (UTC)
You are drawing a narrow distinction between "law" and "theory" that is not well reflected in the way that the terms are used in practice. See physical law for discussion of characteristics often associated with "laws". Ultimately though it is a semantic distinction that is much more important to historians of science than it is actually to scientists. Dragons flight (talk) 18:37, 6 May 2008 (UTC)
To quote that very article: "Simply stated, while a law notes that something happens, a theory explains why and how something happens." I think that's pretty much what I said. --Tango (talk) 20:36, 6 May 2008 (UTC)
My concern, which may or may not have been what you intended, is that your original statement describes laws very emprically and suggests (at least in the way I read it) that laws describe relationships where the explanation isn't understood. In practice though, the expression of most laws isn't merely empirical and is motivated by some underlying theoretical understanding. Hence the line between laws and theory is inherent fuzzy. Maybe I reacted to your original statement differently than you intended. Dragons flight (talk) 16:26, 7 May 2008 (UTC)
Yes, I was a little unclear. Laws are strongly supported by empirical evidence. They are generally explained by theory, but don't need to me (I believe Kepler's Laws were purely empirical for a while before Newton showed they could be derived from his Universal Law of Gravity, for example). Theory, on the other hand, is mainly explanation and isn't particular supported by evidence directly - theories predict laws, which are then supported by evidence. --Tango (talk) 16:33, 7 May 2008 (UTC)
What if gravitomagnetism is proven right? What if antigravity turns out to be possible? What if antimatter turns out to be repelled instead of attracted by matter? Em3ryguy (talk) 20:16, 6 May 2008 (UTC)
Then we'll try and come up with a new theory that fits the new observations. That's how science works. --Tango (talk) 20:36, 6 May 2008 (UTC)
Wasnt that my point? its a theory. a law would be a rule that is not and cannot ever be broken. conservation laws, presumably, cannot be broken. Em3ryguy (talk) 20:58, 6 May 2008 (UTC)
Actually, conservation laws can be broken, albeit for an extremly short amount of time. I believe it's the law of conservation of matter. I don't know of an article about it, but on the science channel there was something that said particles can pop into existence but pop back out in such a short time that there is no effect. It had something to do with the Heisenburg Uncertainty principle allowing it.Zrs 12 (talk) 01:52, 7 May 2008 (UTC)
That's a fundamental misunderstanding of Scientific law and Scientific theory. Law is simply a mathematical proof, while a theory is a broad description of what happens.
That said, I'm confident gravitomagentism will never be proven. Gravity and electro-magnetism are polar opposites (pardon the pun). Magnetism is extremely powerful at close distances, but rapidly loses effectiveness once the distances increase. Gravity retains its strength over long distances, but is overpowered by magnetism on the small-scale. They work very differently. -- Kesh (talk) 21:04, 6 May 2008 (UTC)
You're confused in your example. Gravitomagnetism is a thus far impossible to measure property of general relativity that is unrelated to electromagnetism except that the equations have a similar structure. Dragons flight (talk) 21:09, 6 May 2008 (UTC)
Ahh, thank you for the explanation. The only times I've heard "gravitomagnetism" it was from self-styled Internet Einsteins who thought they had solved every problem in the universe by simply replacing gravity with electromagnetism. The math was horrid, and the logic was worse. -- Kesh (talk) 21:10, 7 May 2008 (UTC)
It is possible for laws to be broken. There's no way for us to know that V will always equal IR (Ohm's law) - it always has up until now, and everything suggests that it always will, but there is still a non-zero chance that it's just been a big coincidence. A law is *not* an absolute statement - that's a "theorem" and is a purely mathematical thing. You might have a theorem that says "given this theory, such and such will happen", for example, given Newton's Universal Law of Gravity, we can mathematically prove the shell theorem, but we still can't be sure that the result of that theorem will always hold, since we can't be sure the law will always hold. --Tango (talk) 12:39, 7 May 2008 (UTC)
Try this, which works in my world.
  • In the humanities etc, "theory" is synonymous with "hypothesis".
  • In the sciences, "theory" is synonymous with "model", and specifically, a model that explains all the existing observations.
Succinct. --Danh, 70.59.79.108 (talk) 23:02, 6 May 2008 (UTC)
Close enough. This is also why it's hard to explain to some people that just because a scientist calls something a theory doesn't meant that it's random conjecture. Proper scientists don't speak in absolute terms, but that doesn't mean they lake confidence, that just means they're real scientists. 206.126.163.20 (talk) 00:23, 7 May 2008 (UTC)
The way I would state it is, both laws and theories are build on axioms (things that must simply be assumed true, probably based on experience and observation). A law can be quite simple (energy is conserved) or it can be more complex (entropy always increasing in time, the definition of entropy being pretty non-trivial--at least quite a bit more than for energy). A theory takes a set of axioms and builds something somewhat complex on top of it; generally a large set of rules and conclusions. Both must be logically consistent in order to have a chance at being useful. We would generally call something a "law" or remove its status as mere "theory" once its axioms have been tested/experienced enough that we are pretty assured of their truth. If a law or theory is completely sound logically, testing the axioms may be done at least in part by testing the law/axiom's conclusions. That's just my take on it though. Think about it and see if it makes sense for you. --Prestidigitator (talk) 00:07, 7 May 2008 (UTC)
Consider this: Not only has Newton's law of gravity been proven to be but an approximation, but some physicists doubt that Einstein's theory of relativity is complete. Imagine Reason (talk) 20:04, 7 May 2008 (UTC)
People know Relativity isn't complete since experiments on very small scales deviate significantly from it. --Tango (talk) 22:21, 7 May 2008 (UTC)

[edit] Infinity

I'm not sure if this belongs here or the mathematics desk or possibly even the philosophy desk, but i'll ask it anyway. Is infinity accepted as being real or is it simply a state which we haven't reached? If that makes sense. I.E. If you divide 100 by 3 you get 33.3 with the .3 recurring. Does this go to infinity or is there a limit?

Regards, CycloneNimrodTalk? 19:01, 6 May 2008 (UTC)

Oh, I don't just mean it as a mathematical context either, anything where infinity is said to exist e.g. at the event horizon of a black hole? Regards, CycloneNimrodTalk? 19:03, 6 May 2008 (UTC)
A Repeating decimal is infinite, yes. Other than that, I'm not sure I understand the question. Friday (talk) 19:05, 6 May 2008 (UTC)
It's a mental and mathematical abstraction. Wisdom89 (T / C) 20:19, 6 May 2008 (UTC)
this is prolly better taken up with the philosophers, because i'm sure someone will come up with something extremely complicated and technical.... but i believe that science and math and people in general accept infinity as being real... it's the basis of our concepts like dimensional space and counting. -ΖαππερΝαππερ BabelAlexandria 21:04, 6 May 2008 (UTC)
I'll give an example. Time. I think most people agree that there must have been a start to time, or do we keep on getting infinitely closer to seeing the beginning? Regards, CycloneNimrodTalk? 21:14, 6 May 2008 (UTC)
Time is a convenient concept created by human beings in order to get up the next morning for work, or know not to go to work on Sunday. It has little to do with infinity. There are entire mathematical branches that deal with infinity starting with calculus ("approaching") and complex numbers (z), but that is scientific. It appears you first questioned maths, then ended off on a more philosophical note. Perhaps infinity was given to us by God, denoting that which cannot be obtained by mere mortals. I can go on. The bounds of one's imagination are infinite. Sandman30s (talk) 21:35, 6 May 2008 (UTC)
Infinity, or its many variants, is a mathematical construct. In the example of 33.333..., or more interestingly 0.999..., the "infinite number" of decimals places merely means that "for any decimal place you find, there is one after it". In the physical sciences, the appearance of infinity - or a singularity - as the solution to an equation generally translates as "things break down here". For example, the event horizon of a black hole is a "removable singularity", meaning that it's weird, but after a change of coordinates it disappears. The centre of a black hole, however, is an "essential singularity", which translates as "general relativity can't tell you what happens at the centre". Confusing Manifestation(Say hi!) 23:19, 6 May 2008 (UTC)
A fun thought experiment that relates to infinity and time (and space) is Xeno's_paradox#Achilles_and_the_tortoise. -- JSBillings 13:28, 7 May 2008 (UTC)

[edit] What does "qsp" in reference to gelatin or perhaps other polymers mean?

I found a reference of "qsp" to gelatin for which I couldn't find a definition on Google. Based on what I did see on Google, it seems to be a unit of measurement for gelatin and perhaps polymers. In the case I refer to, it said "gelatin qsp 100%" Can anyone help define/explain this further?

Thanks! —Preceding unsigned comment added by 65.209.203.254 (talk) 19:11, 6 May 2008 (UTC)

I web searched on "gelatin" together with "qsp" and eventually found some examples where qsp seemed to mean specific viscosity. However, on looking this up, I find that the symbol for it actually uses the Greek letter eta (looks like n with the bottom right corner extended), not the English letter q. In a Google search on both "specific viscosity" and "qsp", many of the results are papers that cannot be freely downloaded, but some hits -- for example this paper in PDF, the 10th hit when I did the search -- show qsp in Google's search synopsis while the actual document has an eta and sp.
So I'm guessing that qsp is being used to mean specific viscosity and the q is a mistake for eta, perhaps originating due to a character-set problem, or else an alternate symbol used if Greek letters are not available.
Either that or I'm completely wrong.
I see that Wikipedia once had a WikiProject Polymers that intended to produce an article on specific viscosity, but the project appears to be moribund. --Anonymous, 20:03 UTC, May 6, 2008.
I think that this probably refers to the reaction quotient for solubility, Qsp. See also Solubility equilibrium. Rmhermen (talk) 16:03, 7 May 2008 (UTC)

If you saw this on a food, drug or cosmetic, it might have actually been USP for United States Pharmacopeia which would indicate the gelatin met standards set by USP. ike9898 (talk) 21:48, 7 May 2008 (UTC)

[edit] Swinging

Why does swinging one's legs when on a swing help? —Preceding unsigned comment added by 76.69.240.138 (talk) 22:05, 6 May 2008 (UTC)

Well, I expect it's about moving your centre of mass, which imparts energy to the swinging. Your weight can be modelled as a point force acting through your centre of mass, and the swing itself as an inextensible string. At rest, the swing hangs straight down, through your centre of mass, so the forces balance out. If you move your centre of mass, you generate a turning moment, which moves the swing as it tries to find equilibrium again. -mattbuck (Talk) 23:53, 6 May 2008 (UTC)
Scientific American had an article in their Amateur Scientist section in March 1989 (unfortunately they don't have that accessible online) The interesting thing was the discussions that article started. Our swing article has a pdf link at the bottom. This site has video that might help answer your question. [6] Lisa4edit (talk) 03:11, 7 May 2008 (UTC)

[edit] Bicycles

Why is it easier to balance a bicycle when it is moving quickly. I asked someone this, and he said that it was because gravity was causing the bike to go in centripetal motion, but I don't think that makes much sense because it should only account for the bike turning. I've tried looking for the answer online, but I haven't been able to find consistent answers. Thanks. —Preceding unsigned comment added by 76.69.240.138 (talk) 23:09, 6 May 2008 (UTC)

Don't nail me to this, but I think it has to do with the force vectors. While you are stationary any forces to the left or right will take full effect. While you are moving forward the main momentum/force is in that direction and the left and right tilts will have less effect. 71.236.23.111 (talk) 23:34, 6 May 2008 (UTC)
Wikipedia has an article on everything....Bicycle and motorcycle dynamics--Shniken1 (talk) 23:43, 6 May 2008 (UTC)
Conservation of angular momentum. It's the spinning mass of the tires that help keep you upright. If you add weight to the tires and go at the same speed, it will be even harder to tip over. Here's a video.--Duk 03:30, 7 May 2008 (UTC)
Took the liberty of fixing your broken link. —Keenan Pepper 05:24, 7 May 2008 (UTC)
Actually, the effect of angular momentum is very minor. It has the role of a steering force, but is not a significant righting force. Our article, mentioned above, discusses all the effects in much detail. --Stephan Schulz (talk) 05:35, 7 May 2008 (UTC)
The effect of angular momentum depends on speed (squared). At slow speeds it doesn't do much, at fast speeds and with heavy tires it does a lot. Riding a large motorcycle is a good example, you can practically hang off to one side and the bike will not tip. --Duk 14:53, 8 May 2008 (UTC)
When you are moving forward on the bicycle, and begin to tilt to one side you use the handlebars to stop the fall by turning the bicycle that way. When you are stationary it does not help! Graeme Bartlett (talk) 22:04, 7 May 2008 (UTC)
I think that's mostly true for low speeds, but once you get going fast enough you don't even need to touch the handlebars. --Duk 03:01, 8 May 2008 (UTC)
But that's still not due to the gyroscope effect. You may be right for motorcycles -- their wheels and tires may have enough moment of inertia, and be rotating fast enough, to gyro-stabilize the bike. But for bicycles it just doesn't contribute much. The tires are intentionally light (because you have to spin them up with your own muscles -- you wouldn't want to do that to a motorcycle tire). Rather, the self-righting effect comes from the geometry of the bike, the way the force from the road tends to act on your front wheel to move it back to the center. --Trovatore (talk) 19:50, 8 May 2008 (UTC)

[edit] Anatomy and physiology

Describe the role of the thymus gland and the Gut-associated tissue (GALT) in the establishment of active immunity —Preceding unsigned comment added by ELVIOTA (talk • contribs) 23:43, 6 May 2008 (UTC)

This looks like a homework question, as as it says at the top of the page, we will not do your homework for you. If you have a specific section you're having trouble with, and you have made an effort to do it youself, THEN we will help. -mattbuck (Talk) 23:50, 6 May 2008 (UTC)
Have you read our article on Thymus - that would certainly be the place to start. --Tango (talk) 23:50, 6 May 2008 (UTC)
For the other part look at Gastrointestinal tract and follow the links there.71.236.23.111 (talk) 01:58, 7 May 2008 (UTC)