Wikipedia:Reference desk/Archives/Science/2008 September 28

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 28

slow step of a reaction

why do we use the slow step of a reaction to determine the rate law of it? —Preceding unsigned comment added by 88.242.107.205 (talk) 00:06, 28 September 2008 (UTC)

Because it's the bottleneck. See Rate-determining step, specifically the funnel analogy. --Bennybp (talk) 00:34, 28 September 2008 (UTC)

Try this analogy on for size: Lets say you went to a party with your friends across town. Your buddy lives like 4 houses down from you, and you drive over to his house, leave your car at his house, and drive like 5 miles across town to the party. Now, he ditches you, leaving you to walk home. So, you have to be at work the next day, and need to know when to leave the party to get home, shower, and get to work on time. You have 2 steps to consider: The time to walk 5 miles home, and the time to drive your car the 200 yards or so back to your house. Do you even consider how long the 200 yard drive is going to take? No, because its miniscule compared to the time it will take to walk your half-drunk ass the five miles back to your neighborhood (not to mention the time you will be kicking your friends ass the next time you see him). The point is, in a multi-step process, where each step occurs at a vastly different rate, the only thing you really need to care about is the slowest step. All other steps happen so fast that they don't add appreciably to the overall time for the process. In chemical kinetics, the rate determining step is often multiple orders of magnitude slower (in other words, it can take 1000 times longer or more than any other step), so we only care about the slowest step. The other steps will not effect the overall time of the entire process to within the limits of our measuring devices. So we can safely ignore them. --Jayron32.talk.contribs 01:39, 28 September 2008 (UTC)

Faster than Light Travel

I was recently in an argument with a friend of mine. I remembered reading somewhere (perhaps in my physics textbook) that if you travel at the speed of light, you stop aging. Travel faster than light and you get younger! Is this information correct? And if so what is the scientific explanation for this? —Preceding unsigned comment added by 203.81.220.111 (talk) 06:28, 28 September 2008 (UTC)

You should read "A brief history of time" by Stephen Hawking. An oldie but a goodie that addresses a lot of stuff like this. Very enjoyable read. NByz (talk) 08:22, 28 September 2008 (UTC)

SpacetimeNByz (talk) 08:24, 28 September 2008 (UTC)

Well first, you can't actually reach the speed of light. See time dilation and the twin paradox for the article and the famous example of phenomenon, respectively. It's not as nifty as it may seem; the person who is aging slower is almost frozen in time as far as the person aging faster can see. So unless you just reeaaallly wanna see the year 3000 AD, it's not terribly useful. Maybe it would work as a very inefficient way of keeping your canned peas good for millenia instead of just years, or a deluxe form of cryopreservation without the cold part... Someguy1221 (talk) 09:23, 28 September 2008 (UTC)

No, it's not correct. There's a certain restricted sense in which "as you approach the speed of light time goes slower." In the limit of v = c "time stops" (though you can't reach that limit). Some people imagine that when v > c time would go backwards, but that's wrong: the formula for the amount of the slowdown is ${\sqrt {1-({\tfrac {v}{c}})^{2}}}$, which doesn't go negative for v > c. Another thing people sometimes fail to appreciate is that the slow time applies to everything; you age "slower" but also think "slower," so you experience a normal lifespan, not a lengthened one. I put "slower" in quotes because, given that everything slows down equally, it's hard to say what it's slower than. -- BenRG (talk) 10:40, 28 September 2008 (UTC)

Though if you do have something that is v > c, I seem to recall its worldline does go backwards from certain reference frames, or something like that (like a tachyon). (But I agree this isn't the same thing as saying something is really traveling back in time at all, much less "getting younger".) --98.217.8.46 (talk) 15:11, 28 September 2008 (UTC)

"Tachyon" is merely a name for some hypothetical thing - they don't exist outside of Star Trek and the math says they can't exist - so let's stop worrying about them. The $v'={\sqrt {1-({\tfrac {v}{c}})^{2}}}$ equation produces the square root of a negative number if v>c -- there are no calculations in the "real world" where the result is a complex number. Even if there were - it's not at all clear what multiplying your age by a complex number would actually mean - but "getting younger" is certainly not it. Essentially, the math fell apart - and that only happens when something impossible is going on. It's a pointless speculation - you can't go as fast as the speed of light if you have any rest mass...so no...just no. SteveBaker (talk) 02:32, 29 September 2008 (UTC)

Another very dumbed-down way I've heard this explained to non-science guys (so, you science guys can skip this so you don't get worked up by it)... By speed, in this case, you are referring to a ratio between your energy and your mass. To speed up, you can add energy, remove mass, or convert mass to energy. The only way to reach the speed of light is to be 100% energy. Since adding energy will not get rid the mass, the only way to do this is to either remove all mass, leaving only the energy, or to convert all the mass to energy. We do both very well. When heat is emitted by your body, it basically separates itself from your mass and becomes 100% energy. You (the mass) don't get any special benefit from it. Also, if you stand in the middle of a large thermonuclear explosion, your mass will quickly and efficiently be converted to energy. You'll suddenly be travelling at the speed of light. However, you won't be you anymore since there is no means of collecting that energy and putting it back together again to recreate you. So, again, you don't benefit much from the experience. -- kainaw™ 02:41, 29 September 2008 (UTC)

No explosion of any kind (even a supernova) is able to convert a person (or anything else macroscopic) entirely into energy; see baryon number. --Tardis (talk) 15:41, 29 September 2008 (UTC)

Protons and Electrons

Are there equal numbers of protons and electrons in the universe? --220.237.34.141 (talk) 07:32, 28 September 2008 (UTC)

No. An electron and anti-electron can combine to produce a photon so that's one less of them for a moment for instance. There is charge conservation though. Dmcq (talk) 10:37, 28 September 2008 (UTC)

Why would the reaction of an electron and an anti-electron be faster (or occur more) than proton + anti-proton?--220.237.34.141 (talk) 11:30, 28 September 2008 (UTC)

Protons and electrons are really very different things. There's little reason to think that many things will happen the same for both. I suspect there's more electrons than protons, actually - electrons are produced naturally through, for example, pair production. Protons are generally not produced in the same way, because protons are much more massive than electrons and hence require a lot more energy to produce. And lets not get started on virtual particles.--Fangz (talk) 12:47, 28 September 2008 (UTC)

I wasn't saying such a reaction occurred more often. Simply that if the numbers were equal and this reaction happened then afterwards they would be unequal. Another reaction might make them equal afterwards but overall in the universe even if the numbets are roughly equal then the odd they are actually exactly equal for any length of time is very very very small indeed. Or perhaps you were thinking almost equal rather than equal? You'd then have to specify 'almost' but I suspect the answer even then as Fangz says is no. Dmcq (talk) 13:16, 28 September 2008 (UTC)

I strongly disagree. If the numbers of protons and electrons were significantly unequal (suppose there were more electrons) - then wouldn't any significant imbalance result in there being a huge negative charge on every macro-scale object? This charge would cause objects to repel each other...and because electromagnetic forces are VASTLY stronger than gravity - wouldn't this cause the immediate spontaneous disintegration of any large objects? The only way I could imagine this NOT happening would be if all of space were uniformly packed with electrons so that all of the repulsions would balance out. But that clearly isn't the case - so why isn't the sun repelling the earth with an ungodly force? No - I think the numbers of protons (or other positively charged particles) must almost exactly equal the number of electrons (or other negatively charged particles)...I don't see how the universe could function otherwise. SteveBaker (talk) 02:24, 29 September 2008 (UTC)

Sorry yes, thinking about it you're probably right. The main place charged particles besides electrons and protons would occur is inside stars but the sun for instance doesn't actually have much happening in it - the reactions like photon to electron and positron or muon conversions are rare compared to the total numbers of ionized atoms and electrons. So the numbers would be roughly equal. Dmcq (talk) 13:48, 29 September 2008 (UTC)

Einsteins starting point

Where did Einstein start when he formulated his special theory of relativity? For instance, e=mc^2, where did he derive this equation from? Related question, what evidence did he have, if any, that his formulae were correct? How did he know that the direction he was going in was the right one? Cheers 59.100.200.162 (talk) 14:09, 28 September 2008 (UTC)

This is a big question. You are probably better off getting an actual book about this than asking us to muddle you through the history of it, which is detailed and complicated. We have a longer article on this (e.g. History of special relativity) but in glancing over it right now, it seems fairly unreadable unless you already know all of the physics involved (and is in my opinion historically dubious—it is history the way a scientist tells it, not how a historian tells it, and makes it look like the history is just a bunch of equations being thrown around in a vacuum).

Conceptually the starting point is just the question of how you can reconcile two things Einstein and his contemporaries knew to be true: the speed of light is independent of the speed of its emitter (it is constant in a vacuum), and that Galilean relativity should hold in all physical frame of reference (Galilean relativity is just why you don't feel like you are moving when you are sealed inside the belly of an aircraft, for example, and why you don't feel like you are moving when you are standing on a rapidly rotating planet—in a wholly-enclosed constant frame of reference you cannot know your own absolute speed by simply experiential means). Both of these facts were things that his contemporaries would have found fairly obvious, but wouldn't have necessarily put them together at the same time.

It is in the reconciling of those two facts that most of SR comes out of—if the speed of light is really independent of the speed of its emitter, despite the fact that physical frames of reference will be relative, then two observers traveling at different speeds will measure the speed of light to be the same no matter what their different relative speeds are, and if that is the case, then all sorts of interesting implications come up about time, space, and etc. I won't go through all of those implications here but that's really where it becomes clear that space and time are deeply, deeply linked.

This is a very poor gloss on what Einstein was really doing and really thinking, though. Again, a good historical book (Walter Isaacson's recent biography is fairly good on this point) will illuminate much more clearly this sort of thing. There were a wide variety of factors relating to Einstein's previous education, his work at the patent office in Bern, his meetings with creative friends, the books he read, and so forth.

As for evidence—for much of Einstein's work, there was not any immediate evidence other than the fact that the work was actually conceptually quite simple and the reasoning seemed to work out. But by itself nobody was all that convinced that it was too important or anything other than playing with math. Most of SR was not proven by experimental means until very late in the 20th century, where observations of things like muons made it clear that indeed going very fast can affect size and time. Einstein did not think all of this work was revolutionary—it just made sense. His work on the quanta was much more revolutionary, and garnered much more attention from other scientists. Only after creating General Relativity, and having a few surprising experimental confirmations, did Einstein become known as a very important figure in physics. --98.217.8.46 (talk) 15:06, 28 September 2008 (UTC)

E=mc² didn't appear in the original paper on relativity, it's from a later paper (though published the same year). There was ample experimental evidence for Einstein's ideas at the time of publication, and in fact all of the math of the theory had already been worked out by Lorentz and Poincaré and others. Einstein's contribution wasn't the math, it was a new philosophical framework for measurement—all the stuff about clocks and metersticks. Prior to 1905 everyone had assumed (without really thinking about it) that there was nothing problematic in principle about synchronizing clocks, though it might be tricky with real, imprecise instruments. Einstein was the first to realize that (a) this was not a philosophically necessary position and (b) it wasn't actually true. I think this was obvious to most physicists once it was pointed out, and the typical reaction to the paper was "of course, how could we be so stupid" and not "that's a strange idea, I wonder if it's true." -- BenRG (talk) 15:12, 28 September 2008 (UTC)

Well and most of the physicists at the time thought Einstein was just being clever with his reasoning—not that it was really very fundamental work. The recognition that the 1905 papers were something amazing didn't come until later. (Quanta notwithstanding—that was taken up by Planck and others.) --98.217.8.46 (talk) 15:15, 28 September 2008 (UTC)

Gary Larson suggested that it was actually a custodian who was key to getting the equation we now know. Can't find a copy of the diagram explaining it right now... DMacks (talk) 20:28, 28 September 2008 (UTC)

I found [1]. PrimeHunter (talk) 02:40, 29 September 2008 (UTC)

Take a look at how close Friedrich Hasenöhrl came in 1904. He had everything but the coefficient. --Arcadian (talk) 00:16, 30 September 2008 (UTC)

Einstein's accomplishment was not that equation itself (which despite its prevalence in popular culture is not one of his most important contributions or his most individual), but all of the reasoning that led up to it. Einstein's real accomplishments were re-thinking the definitions of space and time, which led eventually to a profound understanding of the nature of gravity, and in validating the quanta as a real, physical entity (and not a mathematical trick). His other work is good and impressive but these are the elements that really matter. --98.217.8.46 (talk) 12:55, 1 October 2008 (UTC)

Nightmares

I heard once that being overheated can contribute to the likelihood of nightmares, and it seems to be true for me. Does anyone have information on that? --Masamage ♫ 15:31, 28 September 2008 (UTC)

I've no idea, but I do want to point out that for me, anecdotally, I've noticed that placebo effect on nightmares seems rather significant. I had the idea when I was a kid that if I crossed my arms like a corpse I would have nightmares (hey, I was very young!), and sure enough, as long as I believed it made sense, it worked. When I got old enough to realize how daffy that was, it stopped working. --98.217.8.46 (talk) 15:39, 28 September 2008 (UTC)

More anecdotes, but overheating -> nightmares does fit a pattern I've noticed. It seems to me that my most vivid dreams come when I'm not deeply asleep; that is, when I'm drifting off or just waking up. Perhaps hypnagogic dreams are an influence there. A more widespread notion is that eating certain foods (like cheese or spicy stuff) can increase bad dreams and that could also contribute to broken sleep. Matt Deres (talk) 16:24, 28 September 2008 (UTC)

I would say this is one area where it's rather hard to rule out other factors, like the fact that you are 'overheated' means you're probably not going to sleep comfortably, which probably means you're going more likely to remember any dreams, nightmare or otherwise Nil Einne (talk) 17:15, 28 September 2008 (UTC)

Very true. What may be causing any "overheating" may also be causing nightmares. --Russoc4 (talk) 18:07, 28 September 2008 (UTC)

Interesting. So, can I take this to mean that physical discomfort in general can increase the chance of having dreams with unpleasant elements? (In the case that's making me ask about it, I think I would have remembered it regardless, because the bad thing in the dream caused me to physically struggle and that's why I woke up.) --Masamage ♫ 01:40, 29 September 2008 (UTC)

Generally dreams occur in the lighter phases of sleep, the so-called REM phases. If your sleep is disturbed, by heat, cold or indigestion, for example, then you are less likely to achieve deep (non-REM) sleep and thus experience more dreams. It is possible that being hot may influence the subject matter of your dream but I think the theme of a dream is more closely linked to your present psychological state. 86.4.187.55 (talk) 10:02, 29 September 2008 (UTC)

I believe dream points out that negative emotions are most common in dreams, so simply remembering more dreams in general may give the impression that you are having more negative dreams. -- 21:23, 30 September 2008 (UTC)

Tropical Cyclones sorces

What are other good sources for hurricanes besides the National Hurricane Center's Tropical Cyclone Report.--Leave Message orYellow Evan home 16:11, 28 September 2008 (UTC)

For Atlantic and East Pacific storms, the TCR is the cat's pajamas. But what sort of information are you looking for? Meteorological data? Damage assessments? Predictions? Social attitudes? Government responses? International aid? Demographic data? Seasonal summaries? Historical trends? Economic impact? Cultural impacts? Impact on immigration? You'll need different sources for all of these things. Plasticup ^T/C 18:01, 28 September 2008 (UTC)

A separate but related question: "Cat's pajamas"? That's a new one to me. But I kinda like it.-RunningOnBrains 23:33, 28 September 2008 (UTC)

The question is whether the cat's pajamas is better than the bee's knees... --Jayron32.talk.contribs 02:25, 29 September 2008 (UTC)

They are both the dogs' bol...oh - wait, there are Brit's here who would understand that one! SteveBaker (talk) 02:53, 30 September 2008 (UTC)

A question related to disintegration.

Let's suppose I have a pencil (or a pen, or a wristwatch, or any small object) and I want to completely disintegrate it, destroying every one of its atoms. Can it (theoretically) be done? If so, how? Is it possible to destroy every atom? Thanks in advance. —Preceding unsigned comment added by XxCutexXxGirlxX (talk • contribs) 17:01, 28 September 2008 (UTC)

You could get an antimatter pen Nil Einne (talk) 17:14, 28 September 2008 (UTC)

You could throw it into the sun and let nuclear fusion take its course.

Or you could throw it into a blackhole and allow it to be crushed into a singularity and then evaporated as Hawking radiation. The mass would still exist, but the original atoms would be destroyed forever. APL (talk) 18:55, 28 September 2008 (UTC)

you could just sit back and wait a few months for the black hole at the LHC to suck it in. 96.231.83.176 (talk) 20:02, 28 September 2008 (UTC)

• Throwing it into the Sun won't work. The Sun is only hot enough to fuse hydrogen into helium, not hot enough to destroy all sorts of atoms. (Well, their electrons would be stripped off, but I assume you want the nuclei destroyed.) You need the sort of temperatures found only in a supernova. --Anonymous, 01:35 UTC, September 29, 2008.

A neutron star would be just the thing. None of that hassle with Hawking radiation shooting back the energy of your ex-girlfriend's photo right back at you...forever reminding you...taunting, taunting... SteveBaker (talk) 01:42, 29 September 2008 (UTC)

You could wait. In a mere 10⁴⁰ years, all the protons in the pen should have decayed into mostly neutral pions and positrons. Of course, proton decay is only theoretical. If it doesn't exist, you'd have to wait a bit longer (still only 10¹⁵⁰⁰ years), at which point all the atoms in the pen should have become iron-56.-RunningOnBrains 23:31, 28 September 2008 (UTC)

In old science fiction films, the spacemen carried disintegrator guns. Perhaps one of these gadgets could do the job. Edison (talk) 00:17, 29 September 2008 (UTC)

More seriously, it is theoretically possible (an practically it has been done for some types of atoms) to split large atoms (like metals and carbon) into smaller atoms. If you can do it for one atom, you can do it for each and everyone of them. But you would still have some residual mass of matter. If you want to transform the whole thing into energy, and be left with no mass, then your best bet is antimatter. But why would you want to do that It would require a crazy amount of energy, instead just cuting the link between each of these atoms would make your object puff into various gases without the complexity of spliting the atom --Lgriot (talk) 01:27, 29 September 2008 (UTC)

Most of the above are impractical and could not be done on earth. Your best chance may be to insert into a atomic accelerator synchrotron or Large hadrion collider and zap it with fast moving nuclei, to break up the nuclei. It will be tough to destroy the protons in the hydrogen, so probably immersion in a nuclear reactor could saturate it with neutrons and covert it to deuterium. Graeme Bartlett (talk) 02:33, 29 September 2008 (UTC)

Send it to a priest and have him do some transubstantiation on it. It might look the same but it will really be different. Dmcq (talk)

Um, the annihilation caused by an pen/antimatter pen meeting would wipe out probably the entire continent of North America and points south (depending on where you chose to do this). Just FYI that that's really not a viable way to disintegrate the pen. The black hole thing would be easier.  :) 31306D696E6E69636B6D (talk) 13:23, 29 September 2008 (UTC)

No it would only be equivalent to about the explosion of a small hydrogen bomb. See Mass–energy equivalence, the Nagasaki bomb would have converted about a gram of mass to energy, and when I weighed my biro I could barely make out any movement on the kitchen scales. Not tha I want you doig the experiment anywhere near me NIMBY Dmcq (talk) 14:09, 29 September 2008 (UTC)

For safety reasons, it would be best to do this when the pen was almost out of ink. You would have less mass that way. Franamax (talk) 20:04, 30 September 2008 (UTC)

Whoops, i was thinking of a superdense pen or i was just wrong :) 31306D696E6E69636B6D (talk) 13:33, 1 October 2008 (UTC)

Uranium in homeopathic medicine

I asked a related question yesterday and now I've found this: [2]. It's weird; what's with the "make uranium at home" and "homeopathic uranium" statements? Is this the limit of how dangerous homeopathy can get? Leif edling (talk) 17:15, 28 September 2008 (UTC)

Actually, this sounds almost completely harmless. Crushed "red rock" will bleed negligible amounts of uranium (if any) into the water, and will be quite unlikely to be otherwise harmful. It won't do anything positive, either, but the greatest risk is probably hitting yourself on the thumb while crushing the rock. --Stephan Schulz (talk) 18:01, 28 September 2008 (UTC)

Furthermore, if the homeopathic "remedy" is prepared "properly", the end user is unlikely to be in any danger; thanks to Avogadro's number, all he's getting is water. (Or whatever they're using as the diluent.) -- Captain Disdain (talk) 01:32, 29 September 2008 (UTC)

It's really impossible to make sensible statements about something as obviously stupid as homeopathy - but proponents never properly answer any of the most obvious concerns. A sure-fire test for a ridiculous theory is that it typically falls apart even worse when you believe what the nut jobsexperts in the field are claiming. So let's do that...

Let's suspend disbelief for a moment and assume that homeopathy really worked. I mean, really: We're told that the uranium (in this case) left an "imprint" in the water that did something theraputic - and that this effect gets stronger the more you dilute it. My first concern is how come the few silicon atoms that washed off the glass you mixed it in didn't do something? What about the two human skin cells and the million or so bacteria and viruses that inevitably got in there during the process? Water is NEVER 100% pure - so isn't it going to be "imprinted" with countless other things that it came into contact with? The purer the water you start with - the stronger the effect of the impurities are claimed to be - so using super-clean distilled water only makes the 'pollution' in it even more powerful.

This stuff (if you carefully examine the bottles on the shelves at WalMart) is claimed to have a shelf life of at least a year or two - so the "imprinting" in the water molecules has to last at least that long. Where do they get their "non-imprinted" water? There are claims for homeopathic "cures" for low blood pressure and quite different cures for high blood pressure...but how do you make sure that the imprinting for the wrong "cure" wasn't in the water to start with? You really have no clue whether your water came into contact with a (whatever cures low blood pressure) molecule a couple of weeks before you decided to make a high blood pressure cure with it.

What's worse, they claim that the more dilute you make the stuff, the stronger it becomes - but the prior imprinting imposed on the water BEFORE you start your titration is guaranteed to be made yet stronger by your titrations. Since they dilute (say) uranium to the point where statistics and Avagadro's number proves that there is none of the original stuff left, absolutely ANYTHING that was in the water at least as long as a year ago will be having a super-powerful medicinal effect - even if the water is utterly, 100% pure! I imagine that they get their original distilled water from normal sources - so a year ago, your water was probably a part of the ocean - or floating around in a cloud someplace.

In this particular case, you're being asked to take some reddish granite and use that as the starting point "because it contains uranium" - but it's "rock" - it contains hundreds of other kinds of atoms and molecules. If homeopathy really works - then ALL of those things are also being used to "imprint" the water with whatever things they do to you. The "researchers" in this field cannot possibly have tested all of those other molecules in proper human trials - how could they possibly know that your local flavor of granite isn't going to imprint something really nasty into the water?

The claim is always that homeopathic medicines are 100% safe (which they certainly are!) because - for some inadequately explained reason - they only have "beneficial" effects. But how does the underlying chemistry, physics and biology "know" what is "good" and what is "bad". To cure you of a bacterial infection - it has to kill bacteria. How do these homeopathic imprintings "know" to cure the human and not to cure the bacterium?

The whole theory falls apart so seriously under the most gentle nudges from a scientific mind that answering questions about homeopathy is truly impossible to do - other than to state the bloody obvious - which is "IT CANNOT POSSIBLY WORK - EXCEPT BY THE PLACEBO EFFECT". If it does work by the placebo mechanism then why bother with all of the titrations and other bullshit. Just start a new "cult" that says that drinking water from a magic spring will cure you of everything...oh - but wait - the religious nut-jobsexperts already came up with that one.

SteveBaker (talk) 02:13, 29 September 2008 (UTC)

Answering questions about homeopathy is no different than answering questions about what effecy the witchdoctor's dance is going to have. The basic question is so patently rediculous to anyone that even paid attention in high school that when you say "your just drinking water", people say "no, that can't be it!" and try to find more. Let me restate it. You are just drinking water. If you have a genuine medical concern, find someone who has undergone training in the operation of the human body. If that doesn't work, then ooo eee ooo aaa aaa, zing zang walla walla bing bang... --Jayron32.talk.contribs 02:19, 29 September 2008 (UTC)

Wow! My splitting headache just went away just by reading that! I'm going to cut and paste it and sell it for $100 and there is nothing you can do to stop me because it's under GFDL! :-) SteveBaker (talk) 03:00, 29 September 2008 (UTC)

There's nothing particularly mysterious about homeopathy, the placebo effect is well-documented. It seems as though when someone you trust carefully investigates your symptoms and says "take this, it will cure you", in (I think) about 30% of cases above the baseline, the symptoms are alleviated to at least some degree. The homeopathic concept itself is full of crap, but the placebo effect is a mystery that we should be investigating further. Much as I detest the junk spouted about succussion, there is something to the concept of having individual attention paid to one's health. That of course is what homeopaths do, they draw up an individual profile - which of course renders meaningless the prospect of controlled random-double-blind studies - but also renders inaccessible further studies of the placebo effect. Franamax (talk) 03:12, 29 September 2008 (UTC)

While it may be true that the placebo effect has 30% over baseline positive results, (and I am not sure its that high, but I will accept it axiomatically for the sake of the arguement) any intentional treatment is bound to have much better results. This is especially if your measure for success is that "symptoms are alleviated to at least some degree", since any intentional treatment will already have the placebo effect built in (as long as the patient believes in the cure, the placebo effect should be additive to the theraputic effect of any treatment). While the placebo effect is real and dramatic, its theraputic value is negligible since its effect is true for both real and imagined cures, and the real cures have the added benefit of actually having mechanisms shown to affect the complaint in question... --Jayron32.talk.contribs 03:22, 29 September 2008 (UTC)

Don't forget that part of the placebo effect is measurement error. (That's why you see a placebo effect even in veterinary trials even though the cats and dogs involved certainly don't believe that a trip to the vet will cure what ails them.) I would hate to undergo a treatment whose main advantage is that it makes my doctor think I've improved. APL (talk) 13:47, 29 September 2008 (UTC)

The control group will have the same measurement error so that won't affect the conclusions. --Tango (talk) 15:07, 29 September 2008 (UTC)

Of course. All placebo effect occurs in both control and experimental groups in a properly done experiment. Jayron32 was talking about the "theraputic value" of placebos, I was pointing out that even if placebo effect seems to cause a 30% recovery, only a portion of that will be actual recovery, the remainder will be measurement error. APL (talk) 16:49, 29 September 2008 (UTC)

No, if your experiment is intended to measure the therapeutic value of a placebo then only the experimental group would get the placebo, the control group would get nothing (it is important to never use the results of an experiment for any purpose other than that for which it was intended - trying to measure placebo effectiveness from the results of an experiment comparing a placebo with a new drug is never going to work). The measurements would, however, be the same for both groups, so the error would not effect the conclusion. Also, you're assuming the error would be towards greater affect rather than lesser, what is your reasoning for that? --Tango (talk) 22:27, 29 September 2008 (UTC)

Even that is a slightly tricky experiment. We no longer do "blind" studies (in which the patient doesn't know what he's getting - but the doctor does) - we do "double-blind" studies where the doctor, the patient - and even the experimenter doesn't know who gets what until the study is over. For a placebo to work, it may be necessary for the doctor administering it to be unaware that it's a placebo in order that he can exude confidence that it's actually going to work. That's a tough call in the "nothing vs placebo" case because the doctor knows that it's not a real drug-versus-placebo study because half of his patients are getting nothing whatever. To do it right, you need THREE groups - one gets the placebo, another gets a real drug and the third gets nothing. The guys who are getting the real drug are needed in order that the doctor may believe that he's really treating his patient when he's actually handing out the placebo.

The problem with homeopathy is that it's not just a way to give a patient a placebo - they really do go to all of the ridiculous trouble to dilute the 'active ingredient' a bazillion times - and that costs real money. If you're going to use an expensive process to manufacture your placebo then you might as well use a real drug and get the benefit of placebo PLUS a real drug.

The homeopathic thing that annoys me beyond rage is homeopathic pet treatments. Your pet isn't getting the benefit of the placebo effect - all that's happening is that the owner is spending a lot of money and completely FAILING to treat the animal. That's just horrible. SteveBaker (talk) 23:30, 29 September 2008 (UTC)

You're right, you do need a 3rd group if it's going to be double-blind (which it needs to be). The results from the 3rd group wouldn't be used in forming a conclusion about the effectiveness of placebos though, which makes for a very strange study! Such a study can get other results as well, though - it can show what proportion of the improvement seen in the people taking the drugs was from the drug, what was from the placebo effect and what was just natural improvement. Apparently a study done on antidepressants showed that most of the improvement was natural, most of what was left was placebo and just about 10% was the drug (still statistically significant, but very small). --Tango (talk) 23:36, 29 September 2008 (UTC)

Hmmm - perhaps a yet better study would be to take two groups of patients and doctors - hand out identical placebo to both groups but "leak" the news that the drug is really a sugar pill to half of the people. If the ones who know they are on placebo don't do as well - then there is definitely something to it. SteveBaker (talk) 02:51, 30 September 2008 (UTC)

Hydrogen Bonding

Which would require less energy, moving two particles of the same charge close together, or moving two particles of opposite charges close together ? Why? —Preceding unsigned comment added by 24.215.48.99 (talk) 20:25, 28 September 2008 (UTC)

Visit our Coulomb's law page. DMacks (talk) 20:56, 28 September 2008 (UTC)

Your question is a bit vague. I can interpret it in any of 3 ways:

1. You have 2 particles of identical charge that are X distance apart, and 2 particles of identically opposite charge that are also X distance apart. You try to move them against the natural attraction or repulsion of their charges. At the instant you try to move them, which requires more energy. Well, in the first timeless instant when you move either, the answer is they require the same energy BUT...
2. In the same situation, the two oppositely charged particles will require less and less energy to move because the distance between them (and thus their attraction for each other) is decreasing, BUT the two same charged particles are getting closer, and thus get harder to push. Thus, for any meaningful time interval (that is for any delta-t greater than 0) the same charged particles require more energy.
3. If you are asking what will happen if you push the particles towards each other in both instances, then the answer is that the same charged particles will require more energy, while the opposite charged particles require NO input of energy (they move spontaneously)... In fact they will generate excess energy equal in magnitude to the energy you had to put into the same-charged system to make them move the same amount (assuming of course no friction).

Hope that helps. --Jayron32.talk.contribs 03:15, 29 September 2008 (UTC)

dynamics

suppose you have 2 forces pulling a box, the box is resting on a floor with friction, if the box is not moving because all forces are at equilibrium, then do we still need to worry about friction and include it in the calculation? —Preceding unsigned comment added by 142.151.132.11 (talk) 20:34, 28 September 2008 (UTC)

Is friction a force on the box? If so, does it affect how the box moves when it is pulled? If so, then it is a force that affects the box's motion in response to pulling, and therefore must be included in calculations of that motion and the forces involved. DMacks (talk) 20:48, 28 September 2008 (UTC)

the static friction is on the box, but my problem is, in which puller's direction is the frictional force going towards? —Preceding unsigned comment added by 142.151.132.11 (talk) 21:00, 28 September 2008 (UTC)

Friction opposes "motion", so I'd think consider it to oppose whatever motion would be happening otherwise (i.e., opposite the net force of the pullers). DMacks (talk) 21:38, 28 September 2008 (UTC)

I don't think it changes the result of the calculation, but it could be more complicated than that: if the box is under tension, the friction force could be in both directions on different parts of the bottom of the box. Its sum will be the same as the single force you can calculate instead. --Tardis (talk) 23:09, 28 September 2008 (UTC)

Since the OP didn't say otherwise, I think it is probably assumed that the box is rigid and you can ignore things like tension. --Tango (talk) 23:27, 28 September 2008 (UTC)

I imagined that a more correct answer might be at least interesting (to the OP or someone else) if not necessary. It's not entirely irrelevant: after all, for a stiff box the structural distortions associated with the tension and with the friction are of the same general scale. --Tardis (talk) 23:43, 28 September 2008 (UTC)

In the real world (as opposed to a physics textbook) it could take a larger force to start an object moving than to keep it moving. Edison (talk) 00:14, 29 September 2008 (UTC)

What you have to do is to resolve all of the non-frictional forces on the box - you can reduce them to a single 'net' force. Now you have an easy problem - is the net force able to overcome friction? What gets double-ikky is that for most real-world surfaces, the 'static' friction is higher than the 'dynamic' friction - so once you've established that the static friction is overcome, you have to do the math again with the dynamic friction in order to determine the final motion of the box. Yukky! SteveBaker (talk) 01:37, 29 September 2008 (UTC)

It's also worth keeping in mind that the rule you learn at school — that friction equals the normal force times a coefficient of friction — is only an approximation of a very complex interaction between two surfaces. As it happens, for a lot of practical situations that approximation works remarkably well for its simplicity, at least as long as you remember to use the right coefficient depending on the nature of the contact between the surfaces (static, sliding, rolling, etc.), but one should not mistake it for any kind of "fundamental law". It's a fairly good empirical rule of thumb, nothing more and nothing less. —Ilmari Karonen (talk) 16:32, 29 September 2008 (UTC)

Non-pedantic correction. The OP stated "if the box is not moving because all forces are at equilibrium...". The correct way to think about this is that if all the forces are at equilibrium (ie there is no net force acting on the box) then it will not accelerate (by Newton's first law of motion). So if it's moving it will continue to move in the same direction at the same speed. And if it's at rest WRT the table, it will stay at rest. Actually, this is not a pedantic point, but crucial to the whole of Newtonian dynamics. Enjoy! Robinh (talk) 08:12, 30 September 2008 (UTC)