Wikipedia:Reference desk/Archives/Science/2009 November 2

= November 2 =

Hammerhead Sharks
In what part of the world are hammerhead sharks usually found? The article on them didn't give any specific locations.99.251.239.89 (talk) 00:25, 2 November 2009 (UTC)


 * Hammerhead is a genus name and is pretty broad. Click on the individual species links (e.g. Scalloped hammerhead, Great hammerhead) and you'll see little maps. --Mr.98 (talk) 00:45, 2 November 2009 (UTC)
 * That would depend on which shark you wanted. ~ Amory ( u •  t  •  c ) 00:48, 2 November 2009 (UTC)
 * Cute.  DRosenbach  ( Talk 15:52, 2 November 2009 (UTC)

h1n1 vaccine
hey is there blood in the h1n1 vaccine? i cant find any info on whats in it.--Least0190 (talk) 00:28, 2 November 2009 (UTC)


 * I don't think there is blood (human or otherwise) in any modern vaccine. --Mr.98 (talk) 00:35, 2 November 2009 (UTC)


 * However, there are chicken egg proteins in it, so if you have any allergies to chicken eggs, you may not be able to take that vaccine. See also 2009 flu pandemic vaccine for the H1N1 (swine flu) vaccine, and Influenza vaccine for flu vaccines in general.  -- Jayron  32  00:40, 2 November 2009 (UTC)
 * There most definitely is not. The only people who are injected with any sort of blood are heroin e addicts. ~ Amory ( u •  t  •  c ) 00:40, 2 November 2009 (UTC)
 * For proof (sort of) you can read Hemagglutinin (influenza). Essentially, flu surface proteins cause blood to clump in vitro, which would make for a very ineffective vaccine. ~ Amory ( u  •  t  •  c ) 00:43, 2 November 2009 (UTC)
 * {Sidetrack: While I am personally addicted to heroes, I am doubtful about Amory's claim above that heroin addicts are "injected with blood". There may be blood in dirty needles, but there is, as far as I know, no intent to inject blood. ( Blood dopers may inject blood, but that has nothing to do with heroin.) Is there some treatment technique that involves blood injections for addicts?} Bielle  (talk) 00:56, 2 November 2009 (UTC)
 * Not a treatment by any means - Heroin users who want the hit to hit faster and the high to be higher have been known to stick the needle in their arm, draw a little bit of blood up into the syringe, then inject the mixture back in. It's a great way to OD or get bubbles into your bloodstream, and a really, really, really stupid thing to do, but then so is doing heroin.  Trainspotting features this technique, iirc. ~ Amory ( u  •  t  •  c ) 01:00, 2 November 2009 (UTC)
 * I am now better educated. Thank you, Amory. Bielle (talk) 01:04, 2 November 2009 (UTC)
 * Honestly this doesn't make sense to me. How would this get the heroin to your brain any faster?  I had a vague notion that the idea was precisely to prevent bubbles &mdash; once your blood was up in the syringe, you knew there was no air in the needle.  I don't know whether that makes sense either, but it's more plausible than that it makes you high faster. --Trovatore (talk) 01:43, 2 November 2009 (UTC)
 * Likely there are 2 good reasons for drawing a little blood, 1. you are sure that you are actually in a vein. 2. you ensure that there isn't too much heroin wasted residually in the needle. Unomi (talk) 01:53, 2 November 2009 (UTC)
 * Ah right, the vein thing, I think that was it, not the bubbles. --Trovatore (talk) 04:00, 2 November 2009 (UTC)
 * Well, for one, some people think that mixing powder with water weakens it, so they just put the powder in the syringe, then use the blood to put it in solution. ~ Amory ( u •  t  •  c ) 06:20, 2 November 2009 (UTC)
 * Well, there's one pretty blatant error above -- people who get a blood transfusion are certainly injected with blood, obviously. Looie496 (talk) 02:42, 2 November 2009 (UTC)
 * I left an obnoxious semantic loophole there for myself - transfusions aren't so much injected, per se, as they are dripped. ~ Amory ( u •  t  •  c ) 06:13, 2 November 2009 (UTC)

ok thanks guys its just that i read that it has pig and horse blood in it, i dont want animals blood in me.--Least0190 (talk) 03:27, 2 November 2009 (UTC)
 * If you want it, here's a link. You can read through the full contents of each vaccine, and see that none of them contain anything like that.  The closest you get, as Jayron said, is the possibility of less than one millionth of a gram of egg proteins. ~ Amory ( u  •  t  •  c ) 06:20, 2 November 2009 (UTC)
 * May I suggest for you Carl Sagan's The Demon-Haunted World? Imagine Reason (talk) 19:13, 2 November 2009 (UTC)

Is it possible for energy/ information to travel faster than speed of light in the following case
Let we have a straight pipe AB long but greater than 300,000 km in the free space or vacuum. The pipe is full of small balls of perfect shapes from point A to B and each ball is connected to each other just like two circles at their common tangent point. Assume there is no friction between the pipe and balls. For simplicity we can also ignore the pipe.

Would the last ball at point B be move out if we add a ball to point A of the pipe in less than a second, if not why?

I know nothing can travel greater than speed of light but I'm just asking if it might possible. Thanks 68.147.38.24 (talk) 01:34, 2 November 2009 (UTC) khattak
 * Nothing can be perfectly rigid. The balls are made up of atoms.  When you push on the first ball, what happens?  Its atoms get pushed closer together.  They don't want to be closer together, so they start pushing on other atoms behind them, which move farther away.  This generates a compression wave down the pipe, which moves quite fast, but slower than light.  (It probably moves at about the speed of sound in whatever the balls are made of.) --Trovatore (talk) 01:38, 2 November 2009 (UTC)

Thank you for your swift reply but sorry to ask you again. Would your answer be the same if two persons commune each other by pushing the same whole pipe or rod in dark space against one another? Because there is diference between the pushing speed of atoms and the pushing speed of the whole pipe/ rod 68.147.38.24 (talk) 03:42, 2 November 2009 (UTC)khattak
 * "The whole pipe/rod" is an object composed of atoms. It is no more solid and no more rigid than its full packing of balls. DMacks (talk) 03:48, 2 November 2009 (UTC)


 * Trovatore and DMacks are correct. See "Faster-than-light" for some interesting findings. Axl  ¤  [Talk]  07:10, 2 November 2009 (UTC)

Supposing the rod was made of quark matter?80.2.195.180 (talk) 12:30, 2 November 2009 (UTC)Trevor Loughlin
 * Ho hum, I asked this question a while back - revisiting the archive, I see I forgot to respond, so here's a belated thanks to everyone who answered me. Here is that discussion. Vimescarrot (talk) 13:38, 2 November 2009 (UTC)


 * This question is asked so often that it has made me wonder if we have a template for the constant answer that keeps getting rehashed over and over. -- k a i n a w &trade; 15:09, 2 November 2009 (UTC)


 * Hmmm... I just thought that if I have time today, I will trek through the archives and get a list of links to the previous questions. There should be at least 100 of them.  Then I can make a template that says: "Your question has been asked and answered here and here and here and here and here and here and here...." --  k a i n a w &trade; 15:10, 2 November 2009 (UTC)


 * Hmm... seems like more work than just answering it again, in most cases (or, putting it another way—it is probably easier for four people to recapitulate parts of an answer than it is for one person to look up all of the previous answers. Also more fun, for the four people). This one is common enough in general that we could have just provided Google links—. --Mr.98 (talk) 16:10, 2 November 2009 (UTC)


 * That information cannot travel faster than the speed of light (locally, at least) is a fundamental principle of special and general relativity. Those theories have been very successful at making predictions we have experimentally verified, so we assume that principle is correct. That means that there is a fundamental limit on the rigidity of any object, whatever its composition, since it the speed of sound in it (which is what we are talking about, really) must be slower than the speed of light. --Tango (talk) 18:34, 2 November 2009 (UTC)


 * Short answer: in order to change what is happening, you need to apply a force. Either you force something directly, or apply a force to something which applies a force to something else ... We only have four forces - electromagnetism, gravity, strong, and weak, and all four are transmitted (over long distances) at the speed of light. No force travels faster than light, so your effect can't be transmitted faster than light. -- 128.104.112.149 (talk) 22:15, 2 November 2009 (UTC)
 * What about Quantum entanglement? From the dictionary: a quantum mechanical phenomenon in which the quantum states of two or more objects have at all times to be described with reference to each other, each instantaneously tracking changes to the other, however large the spatial separation of the objects. Instantaneously, no matter what the distance. That's faster than the speed of light. 20.137.18.50 (talk) 17:51, 3 November 2009 (UTC)
 * It's only in a very limited way that quantum entanglement can violate locality. Regardless of quantum entanglement, information can't travel faster than the speed of light, which applies in the case of pushing a long rod.  See no-communication theorem.  Red Act (talk) 18:42, 3 November 2009 (UTC)
 * In short - the quantum states being transmitted are random, so you can't use them to communicate anything other than random values. I did see a proposal that they could be used to communicate a random key for encryption. The encrypted information would then be transmitted by conventional means. --Tango (talk) 18:47, 3 November 2009 (UTC)
 * I got rid of the wrong definition at Wiktionary. The original entry, created on August 10, 2005, was okay, if not very edifying. Five days later it was replaced with the incorrect one, which survived for more than four years. Sigh. -- BenRG (talk) 19:49, 3 November 2009 (UTC)

Billiard ball model becomes sort of invalid when you're talking about this timescale. Why are things rigid? Why do you not fall through the floor? Ultimately there is repulsion between the electron clouds of the floor and the electron clouds of your shoes/feet: an electromagnetic interaction. Indeed, chemical bonds are not rigid: they constantly oscillate (those oscillations get bigger with temperature). It takes time for this repulsion to occur and for it to be transmitted through a substance. (It's the fact that bonds are not rigid that allows for much of carbonyl chemistry and stabilised transition states.) John Riemann Soong (talk) 15:53, 8 November 2009 (UTC)

I think it is difficult to parse in the posit of my second lede but let suppose there is a theoretical ship of one light second long (ab) which can travel with its initial constant velocity say 10 km/sec. There are two persons A and B, a slight greater than a light second apart. A starts the theoretical ship at his end “a” towards B in order to wake him up. Since the distance between B and b is very very small as compared to ab or AB therefore would the end "b" of vehicle be reached B in less than second?

Two persons            A_____________________B Theoretical Ship       a___________________b

68.147.38.24 (talk) 04:06, 9 November 2009 (UTC) khattak

hox and homeotic transformation
"I have a question/challenge on the homeotic gene page. Are HOX actually homeotic? They definitely are in their ability to regulate A/P development (with anteriorization if a paralogous cluster is knocked out), but there are not homeotic transformations of the limbs in knockouts (HOX 10 and HOX 11 Genes are Required to Globally Pattern the Mammalian Skeleton, Capecchi, et al., 2003, Science Vol 301, p363) From this article, while there are gross limb defects, there is not the reassignment of stylopod to zeugopod, or anything along those lines, making me think that these genes are not completely homeotic in nature. Thoughts? Thanks for maintaining this extremely important page." —Preceding unsigned comment added by Terragamo (talk • contribs) 05:06, 2 November 2009 (UTC)


 * I believe the HOX genes are unusual in that respect due to the nature of their distinction in limb development. The differential expression of the HOX genes is established during the limb bud stage, when the future limb is at only a small fraction of its final length, barely extended from the imaginal disc. It'll be a day before I can get back to my old developmental textbook, though, so I should note that that's simply my idea. Someguy1221 (talk) 05:12, 2 November 2009 (UTC)

carbon monoxide
Plants metabolize carbon dioxide. What about carbon monoxide? 71.100.8.110 (talk) 06:20, 2 November 2009 (UTC)


 * They're capable of metabolizing carbon monoxide, but the experiments that showed this exposed the plants to carbon dioxide free atmosphere, so I'm not sure how physiologically significant the effect is. One paper describing this: Someguy1221 (talk) 06:26, 2 November 2009 (UTC)

What happens if a non-depressed person takes anti-depressants?
Not a request for medical advice as I'm just curious about what would happen. Assuming they took them regularly for some time. Would they feel happier, drunk, manic, lose their rational judgment, what? It seems like a scenario for a dystopian science-fiction novel. 78.146.167.26 (talk) 14:58, 2 November 2009 (UTC)
 * The answer is going to depend on which specific anit-depressant drug is taken. Googlemeister (talk) 15:39, 2 November 2009 (UTC)
 * And the dose. --Mr.98 (talk) 16:13, 2 November 2009 (UTC)
 * Don't those drugs sometimes have nasty side-effects? RJFJR (talk) 15:47, 2 November 2009 (UTC)
 * Drug abuse and antidepressant might be a good starting point... TastyCakes (talk) 16:25, 2 November 2009 (UTC)
 * Terrible withdrawals as well if you forget a dose. Readro (talk) 16:56, 2 November 2009 (UTC)
 * Not really. They take several days to begin to take effect. Withdrawal happens after a week or so.--Drknkn (talk) 17:30, 2 November 2009 (UTC)
 * That really depends on the drug (and its half-life). Effexor can cause withdrawal with a single missed dose, the same day you missed it. -- Aeluwas (talk) 18:38, 2 November 2009 (UTC)
 * I was speaking from personal experience, and you managed to guess my brand of pills in one! Congratulations :) Readro (talk) 20:53, 2 November 2009 (UTC)
 * I didn't know about that drug. I've used Paxil, Prozac, and Zoloft. They work slowly.--Drknkn (talk) 21:15, 2 November 2009 (UTC)
 * The vast majority of real-world side effects are mental. Lethargy (laziness), and apathy are common, especially with Zoloft. Anti-depressants do more to curb caring in general than depression. So, you don't feel over-joyed or anything. You'd need a stimulant (like, say, ritalin) for that. If you're already happy, and you take a stimulant, then you'd feel ecstatic. But if you're anxious and you take a stimulant, then the results could be catastrophic.--Drknkn (talk) 17:29, 2 November 2009 (UTC)


 * . Comet Tuttle (talk) 18:04, 2 November 2009 (UTC)
 * This article suggests that some non-depressed people have become habitual users of anti-depressants for "lifestyle" reasons, perhaps after first being prescribed them for reasons other than depression. The user cited in the article does indeed claim that his daily SSRI makes him feel happier, although it is made clear that the effects of using these drugs in this way are unknown and potentially dangerous.   Ka renjc 18:40, 2 November 2009 (UTC)
 * I don't think it's that simple. Depressants like alcohol, for unknown reasons, make people feel good, while stimulants often dampen their enthusiasm. Imagine Reason (talk) 19:10, 2 November 2009 (UTC)
 * Right. I guess it depends on your personality. I've used Paxil, Prozac, and Zoloft over the years. They all make me lethargic and apathetic. Alcohol makes me depressed, but other people get happy when they're drunk, so YMMV.--Drknkn (talk) 21:15, 2 November 2009 (UTC)
 * There are different types of anti-depressants. "Tri-cyclics", "MAOI", "SSRI", and then a bunch which are a bit like SSRIs but have different acronyms, such as NASAs, etc.  Ann and Bob might have very different experiences even of the same dose of the same medication.  There's something called "seretonin syndrome" which can affect people who overdose on soem types of anti-depressant meds.  One way to answer the question would be to look at the side-effects of the medications, and the frequency of those side effects, to see what might happen.  Don't forget the important Placebo Effect either. Remember Civility (talk) 19:33, 2 November 2009 (UTC)


 * Some antidepressants are routinely prescribed for their side-effects, not their anti-depressant effect. See Amitryptiline. I've just come off this drug after 15 years on it for nerve pain: apparently it is the treatment of choice for such pain. I didn't notice a particular anti-depressant effect while I was on it. --TammyMoet (talk) 20:33, 2 November 2009 (UTC)


 * The best conversations of this variety I've had focus on how little one might notice unless in a particular or exceptional situation, or unless they already knew what to look for. Regardless of type taken and mental state before starting, some things that are pretty generic side effects anyone could get could start to appear in just a few days if there's even a minor adjustment in what was already a good chemical balance. Things like... Misinterpretation of intoxication level, headache, light sleeping problems/problems falling asleep, loss of sex drive, difficulty concentrating, unusual fatigue/grogginess are universal. Those are all relatively minor and are pretty easily shrugged off by long-term patients but could feel quite amplified and frightening if you body doesn't quite know what to do with it. There aren't any specific "automatics" as theoretical benefits, and even if there were I can't see why someone would want to put up with the negatives. My biggest concern for someone in "normal" mental health using would be the risk of sudden, um... death? Without a doctor to look over your medical history and put you on a small trial dose of something to make sure you're not allergic in any way, odds are higher of running into some terribly bad side effects like an irregular heartbeat, confusion and blackouts (re: driving), general paranoia, insomnia. Even if none of that ever happened, you'd continuously be at the risk of day-to-day stresses or normal medications throwing things awry; Extreme caffeine consumption, certain cold or allergy medications, prescription painkillers or just extreme fatigue might trigger an undesirable reaction either 'up' or 'down'. This why there will never be any official studies-- it's just too damn unethical to ever have someone take medications like this "just to see". I'd thwap anyone who decided to so something this stupid. ♪ daTheisen(talk) 09:38, 4 November 2009 (UTC)

the form of energy as matter
Harmonic analysis/synthesis reveals that a combination of sinusoidal frequencies can generate an approximate square wave of any amplitude with a virtually infinite wavelength or zero frequency (assuming that in the case of the expression of energy that the reason absolute zero can not be obtained is the same reason absolute zero frequency can not be obtained). Is it possible that this state of combined frequencies is the state of energy we call energy or matter in the form of a particle? Biggerbannana (talk) 15:25, 2 November 2009 (UTC)
 * I'm not really sure what you mean. What are you measuring the frequency of exactly?
 * The wave function of a particle has a non-zero frequency. See matter wave. Rckrone (talk) 17:23, 2 November 2009 (UTC)
 * The idea I am referring to is that of matter or energy being created in a star say by fusion when two atoms of hydrogen becomes one atom of helium. While hydrogen and helium are both matter the energy difference is not expressed in the form of matter but in the form of electromagnetic radiation. The amount of this electromagnetic radiation is known. However, the radiation contains both light and heat and x-rays and Gamma rays and more. However, if you only measure the visible light energy then you come up short and the same for all of the other wavelengths as well but not if you add them all together. When you do add them all together and plot a graph you should get approximately a square wave which itself may have a wavelength near one half the half life of Helium. What I am asking is has anyone else explored this idea and if so have they written a paper? Biggerbannana (talk) 20:52, 2 November 2009 (UTC)


 * A square wave is the sum of an infinite series of sinusoidal waves. Conversely a square wave can be generated by adding together the same series of sinusoidal waves. The frequency of the square wave is that of the lowest frequency sinusoidal wave, so this is not a way to generate a lower frequency wave than one already has. The amplitude of the square wave is less than the amplitude of the lowest frequency sinusoidal wave, shown by the animation. Cuddlyable3 (talk) 22:25, 2 November 2009 (UTC)
 * What would say is the lowest electromagnetic frequency produced by the fusion reaction and its amplitude? For that matter how about the amplitude of each frequency produced? 71.100.8.110 (talk) 02:12, 3 November 2009 (UTC)


 * A single fusion reaction doesn't create a wide spectrum of EM radiation. The energy released is in the form of just one or a few high energy photons and some kinetic energy. Rckrone (talk) 00:09, 3 November 2009 (UTC)
 * Yes and the amplitude and frequency of each...? Have any been measured and added? Biggerbannana (talk) 02:27, 3 November 2009 (UTC)
 * They certainly have been measured, but it depends on what reaction it is and on your reference frame. The point I was making is that the Fourier series of a square wave has countably infinite non-zero terms.  You can't build it out of 1 or 3 or even 100 frequencies. Rckrone (talk) 06:09, 3 November 2009 (UTC)
 * I disagree. Although not a perfect square wave only a few frequencies are necessary to produce a reasonable one with less that maximum amplitude but sufficient duration to trigger a programmable voltage sensor for instance. Biggerbannana (talk) 13:26, 3 November 2009 (UTC)
 * But they don't make anything that looks like that. If you have a reaction that sends off one gamma ray, there's no way to argue that's something like a square wave, and the frequency is somewhere on the order of 1019 Hz, which is a bit off from the theorized half life of a proton which would be less than 10-41 Hz. Rckrone (talk) 17:51, 3 November 2009 (UTC)
 * The fact that the sinusoidal components of a square wave have specific relative amplitudes and phases seems to be overlooked here.Cuddlyable3 (talk) 08:04, 4 November 2009 (UTC)
 * Also not sure how you would measure the amplitudes of each of these components. The Fourier coefficients have to go to zero as the frequency go to infinity, but the energy of a photon grows. Rckrone (talk) 06:45, 3 November 2009 (UTC)

BTW -thanks for whomever provided the graph... 71.100.8.110 (talk) 02:14, 3 November 2009 (UTC)
 * YW. User Kief on Commons made the animation and I posted it. Cuddlyable3 (talk) 11:16, 3 November 2009 (UTC)
 * Much thanks or hugs and kisses if you are female. ;) Biggerbannana (talk) 13:28, 3 November 2009 (UTC)
 * That is the kind of male chauvinist sexist discrimination that belongs to another less enlightened age. Keep your banana to yourself.Cuddlyable3 (talk) 08:00, 4 November 2009 (UTC)

Definition of species
The most common definition of species that I've seen is that a species is a group of organisms that can breed with one another to produce fertile offspring. How are species defined for bacteria and other organisms that reproduce asexually? J4\/4 &lt;talk&gt; 18:15, 2 November 2009 (UTC)


 * Species discusses this issue. Basically, the answer is that there is no good answer. --Tango (talk) 18:30, 2 November 2009 (UTC)


 * It's a controversial area. See "Species" and "Species problem". There are many species that have been renamed/reclassified: Helicobacter pylori (previously Campylobacter/campylobacter-like organism), Moraxella catarrhalis (previously Branhamella), Pneumocystis jiroveci (previously Pneumocystis carinii), etc.. Axl  ¤  [Talk]  18:35, 2 November 2009 (UTC)


 * Species in bacteria have been called 'fuzzy'. Fences  &amp;  Windows  03:17, 6 November 2009 (UTC)
 * In reference to bacterial speciation, you may want to check out bacterial conjugation between 'species'.  DRosenbach  ( Talk 18:00, 8 November 2009 (UTC)

Centrifugal force in Earth's orbit
Are there any observable effects of the centrifugal force experienced on the Earth as a result of its orbit around the sun? (Not the centrifugal force resulting from the spinning of the earth on its axis.) For instance, the weight of an object should be slightly greater when it is between the earth and the sun (i.e. daytime) versus when the earth is between it and the sun (i.e. nighttime). I assume that this weight discrepancy would be too small to measure, but is there any such effect that can be measured? Or perhaps I'm thinking wrong about the whole thing? Thanks- Staecker (talk) 19:56, 2 November 2009 (UTC)
 * There is a tidal force on the Earth due to the sun that causes a noticeable effect. The tidal force on the Earth due to the moon is about twice as big, though.  The tidal forces on the Earth from the moon and to a lesser extent the sun are what causes tides.  Red Act (talk) 20:18, 2 November 2009 (UTC)
 * Indeed. That tidal force is what the OP is describing - the centrifugal force is equal to the gravitational force (in an inertial frame of reference the gravitational force is a centripetal force and there is no centrifugal force, but if the Earth's frame there is). The difference between the gravitational force between two points on the Earth is called a tidal force. --Tango (talk) 20:27, 2 November 2009 (UTC)
 * I'd just add that sometimes the Sun tide and Moon tide reinforce one another (the so-called spring tide), and sometimes partially cancel out (neap tide). This effect has presumably been observed for as long as Man has gone to sea, so yes, the effect is very observable, even if it took a while to figure out the reason. --Trovatore (talk) 20:29, 2 November 2009 (UTC)


 * Tides have nothing to do with centrifugal force. Tides are due to gravity gradient, i.e. the fact that gravity diminishes with distance.  Centrifugal force is due to being in a rotating frame of reference, i.e. in orbit.  If the Earth was falling directly into the Sun instead of orbiting, there would by no centrifugal force due to its orbit, but there would still be a tide.  Conversely, if the Earth was in a circular orbit but gravity was constant regardless of distance instead of diminishing as 1/r², there would be centrifugal force but no tides.  --Anonymous, 06:50 UTC, November 3, 2009.
 * No, that's not so. The centrifugal force is larger on the midnight side than on the noon side.  That still gives you tides.  --Trovatore (talk) 06:53, 3 November 2009 (UTC)
 * Okay, that's a force gradient effect, but it's not a gravitational force gradient effect, therefore not a tide. --Anon, 22:49 UTC, November 3, 2009.
 * Well, it'll make the oceans swell up, so whatever you wanna call it, I guess. From the point of view of Mach's principle it should be the same.
 * A back-of-the-eyelids calculation last night while I was driving home suggests that the centrifugal force gradient should be responsible for one third of the observed tidal effect, not considering the Earth's rotation, which is an approximation I don't know whether you can make or not. Wouldn't stake my life on that being right, but it made sense while driving, anyway. --Trovatore (talk) 23:00, 3 November 2009 (UTC)
 * It must be 100% of it, otherwise where does the rest come from in that rotating reference frame? There is no gravitational force in that frame. Wait, that's not true. There is no resultant force in that frame. The centrifugal force must therefore equal the gravitational force, so presumably they each account for half the tides. --Tango (talk) 23:09, 3 November 2009 (UTC)
 * Centrifugal force is the same as centripetal force, just in a different frame of reference (and in the opposite direction). With constant gravity you would have centrifugal force because you have centripetal force (the gravity). The centripetal force would be constant, therefore the centrifugal force would the constant, therefore there would be no force gradient effects from either force. You can only have tides due to varying centrifugal force if you have a varying centripetal force and it is distinguished from tides only by the frame of reference, so they are as equivalent as gravity and acceleration. You can consider a radial free-fall situation in a rotating reference frame and the centrifugal force will still be there, so if you really wanted to I expect you could reformulate the tides in that situation in terms of a varying centrifugal force (I haven't actually tried, though). --Tango (talk) 23:09, 3 November 2009 (UTC)
 * No, there is no centrifugal force in this problem. I agree with Anonymous, tidal force has nothing to do with centrifugal force.  A centrifugal force in this problem, if one existed, would tend to make the tides higher on the midnight side of the Earth than on the noon side of the Earth.  But in reality, the tidal force raises the tides on the noon side of the Earth as much as on the midnight side of the Earth.  Red Act (talk) 04:03, 4 November 2009 (UTC)
 * To first order, the centrifugal-force gradient also raises the tide the same amount on both sides. The thing to keep in mind is that the two forces balance at the Earth's center.  If the gravitational force were of constant magnitude, but centrifugal force behaved as it actually does, then that would still be true for a circular orbit (I'm not sure if the orbit would still be stable, but that's a separate question).
 * So in this alternative reality with the constant gravity, we have that a piece of water in the noonday sun is subjected to the same gravitational force (from the Sun) as an equally massive piece singing Round Midnight. However the centripetal acceleration in daylight is smaller than that at the center of the Earth, which in turn is smaller by the same amount than that of the water gazing into the starry deep. --Trovatore (talk) 04:21, 4 November 2009 (UTC)
 * (Oh, to clarify: This is still ignoring the Earth's rotation.  Imagine for the moment that the Earth always keeps the same face to the Sun, just to simplify things.) --Trovatore (talk) 04:24, 4 November 2009 (UTC)
 * The Effective potential is a way to rewrite the mechanical equations of motion to make it appear that earth's orbit is due to an "effective" force (centrifugal force) - but all that is really happening is that energy and momentum are being conserved. You can interpret the orbit as a "measurable effect" of centrifugal force in this treatment - but you should be aware of the assumptions made by such a formulation.  Our effective potential article has a good overview of this topic.  Nimur (talk) 20:33, 2 November 2009 (UTC)


 * The centrifugal force you're thinking of doesn't exist here. If the Earth were being swung around on the end of a rope, you would feel yourself pressed toward the Earth if you were on the inner side and pushed away from it if you were on the outer side, and that difference would show up on a scale. But the Sun's gravity accelerates you along with the Earth, so there's no such effect. There is a much smaller effect due to the change of the gravitational field with distance (the tidal force already mentioned), but it's not the same thing. For one thing it's symmetrical—on the near side you're pulled away from the Earth because you're closer to the Sun, on the far side you're pulled away from the Earth because it's closer to the Sun. For another thing the tidal force drops off with distance from the Sun, while a centrifugal force would increase with distance. -- BenRG (talk) 20:46, 2 November 2009 (UTC)
 * Oh please, not this silly quibble again. http://xkcd.com/123 . Oops, sorry, you were making a different point; I hadn't read carefully enough.  --Trovatore (talk) 20:48, 2 November 2009 (UTC)


 * The weight will be greatest when the body is at right angles to the sun or moon, ie at dawn or dusk for the sun. Dmcq (talk) 20:49, 2 November 2009 (UTC)


 * I think BenRG has the right response. I'm pretty sure that what I'm trying to talk about is different from the tidal force, which I know and understand perfectly well. My alleged force would have different properties than the tidal force (read my original description), but if I understand BenRG correctly this effect is cancelled by the sun's gravity. Staecker (talk) 20:54, 2 November 2009 (UTC)
 * One way to think of it is that the Sun's gravity cancels the centrifugal force at the Earth's center. On the noon side of the Earth, the Sun's gravity is greater (because you're closer to the Sun) but the centrifugal force is smaller (because the angular velocity is the same, but the radius is smaller), so you're pulled towards the Sun.  On the midnight side, the Sun's gravity is diminished, but the centrifugal force is larger, and pulls you out. --Trovatore (talk) 21:05, 2 November 2009 (UTC)
 * ... of course this ignores the Earth's own rotation. The angular velocity on the noon side is not exactly the same as the angular velocity on the midnight side, because the Earth is spinning.  I haven't worked out how much difference this makes. --Trovatore (talk) 21:44, 2 November 2009 (UTC)

Mass spec
If I wanted to conduct an analysis of a suite of polycyclic aromatic hydrocarbons in a solvent extract of soil using mass spectrometry in order to obtain information on the molecular masses of the constituents what sort of ionisation and insertion techniques should be used? Thanks 188.221.55.165 (talk) 20:01, 2 November 2009 (UTC)
 * I'm no analytic chemist, but it sounds like you're talking about GC-MS. Seems that's the way people are measuring soil contaminants these days (refs here: ,, will probably have more detail than WP:RD could provide). --- Medical geneticist (talk) 20:32, 2 November 2009 (UTC)

Banging your fists from a different perspective
The act of banging your fists on a table, a relatively common gesture, is usually displayed when someone wants to give their speech a firm and absolute meaning, or when that person is angry. What purpose does this gesture serve from an evolutionary perspective, that is, it obviously serves a purpose nowadays to humans, but is this gesture seen in other primates, and how does this gesture in particular serve us for a certain purpose, instead of using a different gesture. Any thoughts? —Preceding unsigned comment added by 201.21.180.57 (talk) 20:43, 2 November 2009 (UTC)


 * As a layman, I'd suggest that banging one's fist on the table is no more "innate" than rolling one's eyes; our article Gesture is woefully short but has some interesting-looking references. Comet Tuttle (talk) 20:47, 2 November 2009 (UTC)


 * Why make the assumption that this gesture must have an evolutionary "purpose" different than any other gesture? Fist thumping is a useful, easily interpreted gesture.  Various primates (including humans) pound their fists on their chests... probably something having to do with trying to establish dominance or display aggression, etc.  --- Medical geneticist (talk) 21:53, 2 November 2009 (UTC)


 * I'm not sure how biologically relevant it is (I can't find a WP article), but stereotypically male gorillas are thought to pound their chests with their fists in a gesture of physical dominance. Pounding the table could be a related gesture used to connote power and authority. -- 128.104.112.149 (talk) 22:06, 2 November 2009 (UTC)


 * Pounding with clenched fist an object such as a table is expressing an urge to Violence that is in conflict with one's unwillingness to hurt a person. Cuddlyable3 (talk) 22:10, 2 November 2009 (UTC)


 * . Comet Tuttle (talk) 22:31, 2 November 2009 (UTC)


 * See the article Frustration noting the examples. Cuddlyable3 (talk) 07:55, 4 November 2009 (UTC)


 * Not a good reference, as that paragraph not only doesn't support your claim here, but it has no references and is a mass of OR. Comet Tuttle (talk) 18:37, 6 November 2009 (UTC)

Can the Yarkovsky effect be used for space propulsion?
Say you build a probe that heats only part of its exterior using an internal radioactive source. Would you be able to get a net thrust out of this system because of the Yarkovsky effect? I looked around the net for things about such a mechanism but didn't really find anything. 189.15.218.71 (talk) 23:29, 2 November 2009 (UTC)


 * Heating only part of the probe would be hard. You would be better off heating all of it and painting different sides different colours so they emit differently (white on one side so it doesn't emit much, black on the other so it does). That kind of thing has been proposed for giving asteroids a slight nudge over a long period of time so they don't crash into the Earth. I've never seen it proposed for spacecraft propulsion. I guess it would work, but it would be really slow - there are better ways. --Tango (talk) 23:42, 2 November 2009 (UTC)


 * The problem is that radiation pressure at any reasonable temperature (i.e., a temperature low enough to not melt the propulsion system) is very small, generally measured in micropascals. So plenty of energy may be available from the radioactive source, but you're limited as to how fast you can use that energy, i.e., how much power the propulsion system can provide.  That's why nuclear electric rocket designs instead use some kind of electric propulsion system such as an ion thruster, that uses some kind of reaction mass.  Red Act (talk) 00:48, 3 November 2009 (UTC)