Wikipedia:Reference desk/Archives/Science/2010 December 29

= December 29 =

what makes tuning fork prongs oscillate oppositely?
I really like this answer: http://in.answers.yahoo.com/question/index?qid=20100308050035AArgLTA But I don't get one thing. What ensures that the two prongs will oscillate in an exactly inverse way? Naively, I'd think the chances of that happening by chance are infitessimal compared with the chances of their not oscillating at just inverse frequencies when struck.... 87.91.6.33 (talk) 02:11, 29 December 2010 (UTC)


 * p.s. am I also riht that the fork could just as easily have 4, 6, 8, or 12 prongs? In this case, half of the prongs would oscillate one way and half the other??? (inverse frequency) what ensures this?? 87.91.6.33 (talk) 02:11, 29 December 2010 (UTC)
 * For the 1st question, my guess is that the "handle" creates a node. This explains why the two prongs oscillate in opposite directions, because they are really one bent prong with a handle in the middle. Not sure about more then 2 forks, I suppose it's possible but would depend on specifically how it is designed. Vespine (talk) 03:34, 29 December 2010 (UTC)


 * If they didn't start out synchronized, they will rapidly synchronize themself. Watch some of these videos for some examples. Ariel. (talk) 06:41, 29 December 2010 (UTC)


 * I think the answer to this is quite simple: the tuning fork starts out in some combination of equal-phase and opposite-phase vibration, but the equal-phase part is quickly damped out by the mechanism described by that Yahoo answerer. You'll always end up with mirror-symmetric oscillation eventually as long as a mirror-symmetric oscillation mode exists and you started out with at least some energy in that mode. I see no reason why it couldn't also work with 3, 5, ... prongs, since those shapes can oscillate symmetrically too. The oddly titled article Odd sympathy discusses this. I'm not sure I understand what happens to the metronomes on the soda cans, but I think it's somewhat different. -- BenRG (talk) 11:32, 29 December 2010 (UTC)
 * The modal analysis article is worth linking. Nimur (talk) 14:19, 29 December 2010 (UTC)

Why do we fear or 'over react' when something falls from our hand?
Why do we fear or 'over-react' when something falls from our hand (accidentally)? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 04:43, 29 December 2010 (UTC)
 * Because we'd rather it didn't break when it hits the floor? -- Jayron  32  04:44, 29 December 2010 (UTC)
 * I once read that when a woman drops something she tends to throw her hands back and step back, as if avoiding anything further to do with the falling object at that moment, while a man will use all his limbs in a seemingly desperate attempt to slow the object in its fall to the floor. Some random original research would seem to support that view, but I have no idea if it's more broadly true. HiLo48 (talk) 05:48, 29 December 2010 (UTC)
 * I suspect whoever wrote that was completely making things up, either based on a small selection of people they had known to drop things, or just because it matched how they thought the world worked. It doesn't fit with any of my personal experience or observations, nor does it seem at all consistent with anything I have read on the actual science of gender differences. Did you, perhaps, read it in a fiction book? 86.164.67.8 (talk) 17:41, 29 December 2010 (UTC)

Not just breakables. We do have a jerk when things slip out of our hands. —Preceding unsigned comment added by 125.21.50.214 (talk) 05:50, 29 December 2010 (UTC)

It probably has something to do with dropping babies.  Sean.hoyland  - talk 12:16, 29 December 2010 (UTC)


 * It may be a counterpart to an impulse a highly developed capacity to grasp. The hands are used to hold onto something, and they do that under a wide variety of circumstances and over extended periods of time. The hands of humans are very well developed in this area and there is probably complex mental functioning supporting the grasping functions of the hands. The realization that there is a failure in that function probably causes complex mental reactions. Somehow, I would guess, that leads to overreaction, or fear. Bus stop (talk) 12:25, 29 December 2010 (UTC)


 * The answer to this, I think, is actually quite complex. The mechanism is actually a way of speeding reaction times, but the way we perceive it is shaped by some special brain mechanisms.  Some of the factors that come into play are discussed in the article Neuroscience of free will, especially the section relating to reaction times. Looie496 (talk) 16:36, 29 December 2010 (UTC)


 * It think it is a VERY good question, I would love to read a study on this, my emotional state when I drop something insignificant is, for 1 or 2 seconds, completely an over-reaction, given the non-gravity of the situation. Maybe Sean or Bus are onto something here. --Lgriot (talk) 14:15, 30 December 2010 (UTC)


 * If it is a food item and you are a proto-human you may lose that food item: a fellow of your own species may pick it up and run away. Bus stop (talk) 19:56, 30 December 2010 (UTC)
 * Totally OR: Remnant from our tree-dwelling monkey-like ancestors? They evolved a fear of dropping things, because it would very frequently mean you loose it forever, and the only things a tree dwelling creature would we have in their hands is either valuable food, or ideed as mentioned above, a baby. Droping any of of the 2 would have either serious or extremely serious evolutionary consequences? --Lgriot (talk) 09:35, 31 December 2010 (UTC)


 * This is interesting:


 * Contrary to popular opinion, humans - homo sapiens - are not the only primates possessing opposable thumbs. Chimpanzees and monkeys can oppose the thumb to the index digit. What makes the human hand unique in the animal kingdom is the ability of the small and ring fingers to rotate across the palm to meet the thumb, owing to a unique flexibility of the carpometacarpal joints of these fingers, down in the middle of the palm. This is referred to as "ulnar opposition" and adds unparalleled grip, grasp, and torque capability to the human hand. This feature developed  after the time of Lucy, a direct human ancestor, who lived about 3.2 million years ago.


 * And from the same source:


 * About a quarter of the motor cortex in the human brain (the part of the brain which controls all movement in the body) is devoted to the muscles of the hands. This is usually illustrated with a drawing of a human figure draped over the side of the brain, body parts sized proportional to the amount of brain devoted to their movement, referred to as a homunculus - as illustrated in this drawing from Dr. Wilder Penfield's monograph "The Cerebral Cortex of Man." (the illustration is at that source)


 * Inadvertently dropping something from one's hands requires an immediate response under certain circumstances.


 * WP:Original Research: Due to the complexity of the hands and their functions, the response is automatic, thus we overeact when the dropped object is unimportant. Bus stop (talk) 14:29, 31 December 2010 (UTC)


 * The comment above about men-v-women on this issue reminds of an incident from my own life. A female coworker and I found ourselves in a van with a flat tire. An older Chevy Astro as I recall. I jacked it up and took the flat off. Right as I did that the jack sank suddenly into the soft earth and the van began to tilt and was seemingly going to fall. I grabbed the edge of the wheel well and pulled for all I was worth, and began urging my co worker to retrieve the jack and re-position it. She had already backed up to a safe distance outside the path of the tilting van and laughed at the very suggestion that I could hold this van up while she crawled underneath it and recovered the jack. She was probably right, and I would have hated to crush her skull or spine that day, but it rather shattered my illusion of being Superman. Beeblebrox (talk) 00:01, 2 January 2011 (UTC)

What kind of holly?


What kind of holly is this? I never realised that there were multiple holly species until this evening, when I discovered that there were lots of different categories at Commons for different species of holly. Nyttend (talk) 05:04, 29 December 2010 (UTC)
 * I'm not sure we can tell from that one picture. There are literally hundreds of different species and/or hybrids of Holly, and many are likely to be indistinguishable execpt by careful, direct, examination by a knowledgeable botanist.  See Holly for an idea of the problem.  Browsing through several of these that have pictures in the articles, I can't find much to distinguish them either from each other, or from your picture.  -- Jayron  32  05:17, 29 December 2010 (UTC)
 * Hmm. Sorry to have asked an unanswerable question; thanks for trying.  Nyttend (talk) 16:16, 29 December 2010 (UTC)

Dark energy and antimatter
Hello. Is antimatter attracted or repelled by dark energy? Is there anything in the universe which is attracted by dark energy? Thanks in advance.--Leptictidium (mt) 11:32, 29 December 2010 (UTC)
 * Dark matter interacts with other matter (including antimatter) gravitationally. This interaction is always attractive. --Wrongfilter (talk) 12:58, 29 December 2010 (UTC)
 * Dark energy (not dark matter) is basically another way of looking at the metric expansion of space. As such, it's a property of the vacuum, rather than something to do with matter, so normal matter vs. antimatter is irrelevant.
 * The consensus among physicists is that the gravitational interaction of antimatter is attractive, although that hasn't actually been experimentally confirmed yet. But again, that's actually irrelevant to a discussion of dark energy.  Red Act (talk) 14:46, 29 December 2010 (UTC)
 * Oh dear. Sorry, I misread. --Wrongfilter (talk) 15:02, 29 December 2010 (UTC)


 * I'd like to add that it is unknown whether or not dark energy is a property of the vacuum. That is a leading theory, but alternative theories (such as quintessence) would allow the repulsive effects of dark energy to be associated with some new type of particle.  Since we don't really understand what causes dark energy, it is safe to say that there are lots of possible explanations.  Some are more plausible than others.  Dragons flight (talk) 18:34, 29 December 2010 (UTC)

How much damage would a missile do?
Let's say a Hsiung Feng IIE missile was fired into the middle of Central, Hong Kong at rush hour. How much damage would it do? How big would the crater be? How many people would it kill? (A dozen? Hundreds?) 122.61.218.145 (talk) 12:04, 29 December 2010 (UTC)
 * It depends very much on the actual warhead. With a dead weight, maybe around a dozen. With a HE warhead, I'd guess hundreds. In both cases, there would be a very large spread of possible outcomes. If you assume WMD loads, the numbers can become much higher. --Stephan Schulz (talk) 14:02, 29 December 2010 (UTC)
 * With due respect, the OP's scenario is worrying about cruise-missile targeting from the vantage point of "concerned citizen," and not from that of a "geopolitical strategist." Most reliable references on the strategic implications of cruise-missiles focus on their cost-benefit analysis; and most rational strategists would opt to target airports and air-bases, not busy city streets.  Cruise Missile Proliferation in the 1990s discusses details and specifications some of the various missile capabilities known to exist in various countries.  The Cruise Missile Challenge, a policy report published by independent agency CSBA, gives a good overview of cruise missile politics, cost, and even discusses their potential strategic use in the Taiwan Strait conflict.  Bear in mind, cruise missiles are really expensive - and Taiwan doesn't have many of them; so strategically, the most significant targets for them would be military airfields (where a single strike could incapacitate hundreds of millions of dollars of enemy aircraft).  Airbase vulnerability to conventional cruise-missile and ballistic-missile attacks, published by the infamous RAND Corporation, provides a stunningly (and frighteningly) detailed scenario of potential damage (and vulnerability of) an American air-base to an enemy cruise-missile attack; and it lays out the cost-benefit analysis of strategic and tactical missile strikes.  Regarding blast range, collateral damage, casualties, and targeting effectiveness, of course that sort of detail would be highly confidential; but you can easily estimate the power of a 200 kg warhead and the probability of landing on a crowd of any particular density of people-per-square-meter.  (But you can see maps, diagrams, and blast-radii in that altogether terrifyingly descriptive RAND book).  Ultimately, keep in mind that military use of cruise-missiles against civilian targets is both expensive and geopolitically stupid - the world does not look kindly on the use of powerful technological weaponry against civilian targets.  Taiwan would be unwise to expend its very limited stockpile of tactical or strategic missiles against a civilian target; each missile fired at a civilian target would clearly aggravate their adversary; and simultaneously, it would do little to impede the Chinese military capability for retaliation.  Nimur (talk) 14:10, 29 December 2010 (UTC)
 * Also, deliberately attacking the civilians of your enemy is prohibited by the Fourth Geneva Convention (1949). You can, say, attack the Ministry of War's building, even if doing so will cause civilian casualties, but you can't launch attach that will solely cause civilian deaths. CS Miller (talk) 15:29, 29 December 2010 (UTC)


 * When was the last time a world-class business city was attacked by a state's armed forces using big-enough-weapons? The city must be a key player in international business (e.g., NY, London, Tokyo, HK ...). Did it ever happen after WW2? The Chinese civil war (-1949) was not a war between two countries. Berlin was only denied land-based access by the Soviets. Seoul was not an international business city at the time of Korean war. 1950s and 1960s Saigon might have been a large city however Vietnam as a French colony was not very "international". Beirut has always been a regional city. The 9/11 attack was not ordered by any country. Baghdad certainly was not very international. -- Toytoy (talk) 18:12, 29 December 2010 (UTC)
 * What's a 'world-class business city' ?  Sean.hoyland  - talk 18:15, 29 December 2010 (UTC)


 * I can't define it. However, it must have a certain percentage of investments from many major 1st world countries. As a result, if you attack this city, investors could get very angry at you. You not only make the victim country very angry, but you also make many other 1st world countries very very unhappy. Let's say I bombed a small town in Kansas. People around the world may never heard of that town (population 32). They do not get very angry. But if I bombed London or Paris, people all over the world knew the city, many people have money in these cities, they get very very very angry. -- Toytoy (talk) 18:21, 29 December 2010 (UTC)
 * I asked because 'When was the last time a world-class business city was attacked by a state's armed forces using big-enough-weapons?' is quite an interesting question that I don't know the answer to....um...Kuwait City, Belgrade...maybe...I'm struggling.  Sean.hoyland  - talk 18:35, 29 December 2010 (UTC)

The Hsiung Feng IIE's modern 200 kg high explosive payload might be roughly comparable to the WW2-era 980 kg Amatol payload of the German V-2 missile. The worst loss of life in a single V-2 attack was 160 killed and 108 seriously injured and a modern reconstruction (see article) demonstrated that the V2 creates a crater 20 m wide and 8 m deep. Cuddlyable3 (talk) 22:19, 29 December 2010 (UTC)
 * Note of course modern Hong Kong in many parts has a much higher population density then pretty much anywhere in wartime England I would guess Nil Einne (talk) 19:55, 30 December 2010 (UTC)

Elipitical Orbit
I would like to know whether the orbit of a planet/satellite become an elipitical orbit if its tangential velocity is reduced or increased beyond the confines of a circular orbit. References preferable. --Tyw7 (☎ Contact me! • Contributions)   Changing the world one edit at a time! 12:35, 29 December 2010 (UTC)
 * Yes it does (in both cases), at least as long as an increase in velocity is not so large as to make the orbit unbound (i.e. parabolic or hyperbolic). In the spherically symmetric gravitational field of the central body any (bound) orbit is periodic, i.e. the satellite has to return to its original position. If you decrease the velocity, that point will become the apocenter (i.e. the point farthest from the central body) of the elliptical orbit, if you increase the velocity it will become the pericenter. --Wrongfilter (talk) 12:57, 29 December 2010 (UTC)
 * Regarding references: I highly recommend the book To Rise From Earth, which provides a straightforward explanation of orbital mechanics that is accessible to any interested reader (even if they don't have a firm background beyond basic algebra). This book is intended to introduce the concepts and basic mathematics of spaceflight without requiring a full-blown degree in astronautics.  It is suitable for anyone with at least a junior-high or high-school level of algebra, and claims to use "no equations" to describe orbital mechanics (though I seem to recall a few).  There are also plenty of textbooks that study this subject in greater details, if you do have at least some background in basic calculus and physics.  And if you are interested in professional grade space navigation, NASA provides DESCANSO, a compendium website of educational and technical resources, including free textbooks, for Deep Space Communications and Navigation systems that will hold nothing back on the "details."  (After all, if you want to point your communications antenna at an interplanetary probe, you had better calculate its orbit exactly - no "approximations").   Nimur (talk) 13:41, 29 December 2010 (UTC)
 * Interacting objects in orbit and orbital resonances may increase the eccentricity of both orbits in proportion to their masses. Pluto and Neptune are an interesting pair. ~ A H  1 (TCU) 17:34, 1 January 2011 (UTC)

Does cancer cause hair to fall out?
Or does the treatment like chemo cause the hair to fall out? ScienceApe (talk) 18:34, 29 December 2010 (UTC)


 * Chemotherapy is what causes it to fall out. thx1138 (talk) 18:41, 29 December 2010 (UTC)


 * Radiotherapy and many (but not all) forms of chemotherapy rely on the greater susceptibility of rapidly dividing cells to DNA damage. While the malignant cells targeted by these therapies certainly fit the bill, there are a few other places in the body where normal cells divide rapidly; it is the sensitivity of these tissues that often establishes the maximum tolerable dose for these therapies, and which is responsible for many of the side effects associated with these treatments.  Quickly dividing cells in bone marrow, the lining of the gastrointestinal tract, and in hair follicles are all sensitive to DNA-damaging treatments, leading to (respectively) anemia, (some of the) nausea, and hair loss associated with certain types of cancer treatment.  With radiation therapy, hair loss will only occur within the areas exposed to ionizing radiation; with systemic chemotherapy hair loss can be widespread.  TenOfAllTrades(talk) 19:39, 29 December 2010 (UTC)

Animal slime?
With regards to the slime secreted by slugs/snails, frogs, fish, eels, etc. - is it all the same basic stuff, regardless of the creature that secreted it (I guess that some animals can add toxins and irritants to it)? If so, is there a an easily writeable chemical formula for this substance? --95.148.109.133 (talk) 18:54, 29 December 2010 (UTC)


 * The technical term is mucus, and as that article tells you, the most important components are a variety of proteins. Looie496 (talk) 19:02, 29 December 2010 (UTC)


 * Many animals can make mucus including some single cell protists. Glycoproteins are abundant. Graeme Bartlett (talk) 20:13, 29 December 2010 (UTC)
 * And as for a single chemical formula, proteins have incredibly complex chemical formulas (Beta Actin has an MW of around 42,000 If I recall). Googlemeister (talk) 15:25, 31 December 2010 (UTC)

Intelligence of a sleeping human
How intelligent is someone who's asleep, but not dreaming? While I'm at it, what about animals? — DanielLC 20:48, 29 December 2010 (UTC)


 * That's kinda like asking "What is the blood type of someone who's asleep". Even ignoring the fact that "intelligence" is a nebulous, unmeasurable quality to begin with.  So, insofar as someone has a measurable thing called "intelligence" at all, it shouldn't be different just because they are asleep.  Since someone cannot take an intelligence test while asleep (indeed, one cannot take any test while asleep) it seems a silly proposition to begin with.  Animal intelligence is even more difficult to assess; we can measure animals on their ability to perform certain tasks (such as run through mazes or pfoint at pictures to get food), but exactly how or why these tasks might indicate "intelligence" is pretty difficult to assess.  -- Jayron  32  20:56, 29 December 2010 (UTC)


 * You can still respond to stimuli while asleep. You can't take an IQ test, but neither can any animal except a human. Can't they still test your intelligence the same way they test that of an animal? I don't see why intelligence would be the same when you're asleep. People have been known to walk and talk in their sleep, and they certainly don't act as smart as people who are awake. — DanielLC 21:23, 29 December 2010 (UTC)
 * Actually, people have been known to perform highly complex activities while sleepwalking (although our article, Sleepwalking, says such claims are disputed). --Tango (talk) 21:28, 29 December 2010 (UTC)


 * What particular measure of intelligence do you propose? The WAIS may be difficult to administer to someone who is unconscious.  As I stated, the very concept of quantifying intelligence is problematic even for humans.  Its hardly a rigourous, scientific thing.  This is even moreso for animals; assigning a quantity, which may not have any real meaning, to a subject which cannot even be tested for that quantity, is doubly meaningless.  -- Jayron  32  21:29, 29 December 2010 (UTC)
 * And you can't test the intelligence of a sleeping animal anyway. Intelligence is not something floating around in your blood. When they talk of animal intelligence, they either talk in very large generalizations regarding the forebrains of an entire species (which you could do about humans, too, but it doesn't tell you anything surprising, asleep or otherwise) or they talk about things like problem solving, which require being awake to measure. --Mr.98 (talk) 22:29, 29 December 2010 (UTC)
 * I wouldn't recommend a test designed for humans. How do they compare the intelligences of animals? Can't they also do stuff like use an MRI to see what sections of the brain are being used, an other tests to see what those sections actually do?
 * Looks like I forgot to sign that. Isn't there supposed to be a bot for that? — DanielLC 00:39, 30 December 2010 (UTC)


 * "...one cannot take any test while asleep" Not so: Multiple Sleep Latency Test, Polysomnography. Mitch Ames (talk) 01:15, 30 December 2010 (UTC)


 * If you included dreaming I'd say just as intelligent as the person was when awake, but with a distorted perception of reality. 82.44.55.25 (talk) 21:26, 29 December 2010 (UTC)

Sleep (see article) is clearly a period when the person does not demonstrate their intelligence. For example, the sleeper is oblivious to unexpected dangers and will not converse. However experiments in sleep deprivation show that sleeping has a rejeuvenating effect on memory whose health is essential to intelligence, see the article Sleep and memory. Higher mental activities such as learning and creativity (see articles) can also occur during sleep. A possible answer to the OP is that the sleeper's mind is liberated from its survival needs to be intelligent, conscious and coherent, but that all the mental resources to be so are present in latent form. The Autonomic nervous system continues in sleep to control essential functions such as heart rate, respiration and digestion but these are classed as evolved rather than intelligent functions. Cuddlyable3 (talk) 21:55, 29 December 2010 (UTC)


 * They don't show much intelligence. There's still some. — DanielLC 00:39, 30 December 2010 (UTC)


 * Intelligence during sleep can manifest as the creation of dreams which are full of puns, and which relate recent events to meaningful events and themes in one's history. Dreams are often forgotten within seconds of waking, but occasionally I have been able top recall dreams which would be amazing works of creative writing if done during waking hours. Edison (talk) 19:41, 30 December 2010 (UTC)


 * Famously, August Kekulé solved the structure of benzene in a dream. Wnt (talk) 03:00, 31 December 2010 (UTC)


 * Lucid dreaming implies some intelligence while asleep. Mitch Ames (talk) 03:53, 31 December 2010 (UTC)
 * I don't see why it needs to be lucid. The only difference between lucid dreaming and the ordinary kind is that you've figured out that you're dreaming.  Knowing that fact is not a necessary condition to exercise cognition, nor to be conscious (in the sense of phenomenal consciousness).
 * It doesn't need to be lucid, but it does need to be dreaming. I specifically asked when you're not dreaming. — DanielLC 01:51, 1 January 2011 (UTC)
 * In fact I don't think it's necessary even to be dreaming. I'm pretty sure there are times that I am asleep, but both phenomenally conscious and exercising cognition. --Trovatore (talk) 03:59, 31 December 2010 (UTC)
 * I'm interested in the times when you're not. — DanielLC 01:51, 1 January 2011 (UTC)
 * Logical reasoning may be impaired during a dream. The lucidity of a dream may impact many factors you describe. ~ A H  1 (TCU) 17:33, 1 January 2011 (UTC)

Oxygen difluoride
Is it a colorless gas? --Chemicalinterest (talk) 21:06, 29 December 2010 (UTC)
 * Apparently. For these sorts of questions about the appearance of chemical compounds, a Google search for something like oxygen difluoride appearance generally gives pretty good results. TenOfAllTrades(talk) 21:57, 29 December 2010 (UTC)
 * True, but it's always nice for it to be confirmed by those of us with access to the standard reference sources! Colourless gas that condenses to a pale yellow liquid. Physchim62 (talk) 15:17, 30 December 2010 (UTC)