Wikipedia:Reference desk/Science
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April 15
Stomach safety - Uncooked rice?
If you eat uncooked rice will you explode? 71.100.160.118 00:31, 15 April 2007 (UTC)
- Don't know about that, but googling "uncooked rice" "safe to eat" turns up several sites that say uncooked rice may contain harmful bacteria. Anchoress 00:36, 15 April 2007 (UTC)
- Sounds like a change in "the old wives tale" that feeing rice to birds will make them explode. The closest we've found is exploding bats I do think. [Mαc Δαvιs] (How's my driving?) ❖ 08:03, 15 April 2007 (UTC)
- There was a mythbusters episode about how to detonate a pigs stomach using soda. The stomach (without the pig) was sealed at both ends and filled with soda and water like a balloon. The expanding carbon dioxide caused the somach to rupture. —The preceding unsigned comment was added by 84.187.46.16 (talk) 12:54, 15 April 2007 (UTC).
- Eating large quantities of uncooked rice and then drinking large amount of water can be very dangerous to your health as it can cause your stomach to rupture. I think it has been used as a method of torture before. --80.229.152.246 16:41, 15 April 2007 (UTC)
- Er how? Ever soaked rice overnight for some dishes? They don't bloat as if they're cooked. --Wirbelwindヴィルヴェルヴィント (talk) 19:33, 15 April 2007 (UTC)
- Maybe that "method of torture" is like force feeding, or gavaging.
overnight in the dishes is not as hot as your stomache. [Mαc Δαvιs] ❖ 03:18, 16 April 2007 (UTC)
1 − 2 + 3 − 4 + · · ·
I didn't see it anywhere in the article, so I'm asking here... Does the subject of today's featured article, 1 − 2 + 3 − 4 + · · ·, have any useful purpose or is it just some mathmatician's noodling? Dismas|(talk) 02:14, 15 April 2007 (UTC)
- Like lots of math, it may not have an obviuos application, but is interesting nonetheless. THe fact that the series sums to 1/4 when it is divergent is especially interesting —The preceding unsigned comment was added by 88.110.28.251 (talk) 02:19, 15 April 2007 (UTC).
- It's a "counterexample" to conventional notions about convergence, suggesting that there is more depth to the subject than might be initially assumed. Nimur 04:54, 15 April 2007 (UTC)
- Yes, it is noodling, although to describe Leonard Euler as "just some mathematician" is like calling Shakespeare "just some playwright" or Mozart "just some composer". Most pure mathematics is "noodling", or at least starts out as "noodling", and is none the worse for being so. Gandalf61 08:48, 15 April 2007 (UTC)
- The importance of such puzzles may not be understood at the time the mathematician works on it - but it is amazing the number of seemingly irrelevent 'puzzles' that later became critical to human progress. A ton of work was done on prime numbers (for example) that seemed to be pure number theory with zero practical applications at the time, now have critical importance in cryptography - and hence the ability to do business safely on the Internet. I'm not aware of any important applications of the summation of this particular series - but I'd bet good money that the techniques that had to be developed in order to solve it are key to all sorts of modern tools and applications. SteveBaker 15:48, 15 April 2007 (UTC)
- As I said on the article's talk page, it's utterly pointless. Satisfying idle curiosity, as most of math does, does not benefit humanity, and so is worthless. Vranak
- "There is no branch of mathematics, however abstract, which may not someday be applied to the phenomena of the real world." (attributed to Nikolai Lobachevsky, but unsourced in wikiquote) ---Sluzzelin talk 17:52, 15 April 2007 (UTC)
- As I said on the article's talk page, it's utterly pointless. Satisfying idle curiosity, as most of math does, does not benefit humanity, and so is worthless. Vranak
- Key phrase: may someday. Vranak
- Vranak, same thing can be said about refinement in most arts, creating the music you listen too, the design of the clothes you wear, the chair you are sitting in, etc. (Geez, why am I replying to this obvious troll).
- The uncertainty of evaluating expressions like that is one of the things that brought about late 19th and early 20th century formalism. This is how we know it does not have a sum. Root4(one) 18:04, 15 April 2007 (UTC)
- Music does not satisfy idle curiosity. Chairs do not satify idle curiosity. Clothing does not satisfy idle curiosity. Vranak
- I don't know how much time you've spent doing science, Vranak, but one of the astounding things that happens is that you find yourself needing the answer to some fantastically obscure side question that's just come up in your work, and you do a literature search, to discover that, in fact, someone has not only answered that question but also published a peer-reviewed paper about it. They did this even though they had no idea whether anyone would find the result practically useful. They may never hear about the day you did actually find the result practically useful. But in the end, it was, it was.
- Doing pure research, without regard to applicability, is in some ways a luxury. And it's an expensive luxury, to boot. But it has absolutely incalculable value in terms of its ability to eventually, and in a million subtle ways, enable actual life-changing new developments, without which life as we know it could not exist.
- You can dis and refuse to pay for pure, "pointless" research if you want to, but unless you disavow yourself of all human technology, and revert to pretty much a hunter-gatherer lifestyle, you're being somewhat of a hypocrite. —Steve Summit (talk) 18:37, 15 April 2007 (UTC)
- I don't know where to begin with this. I understand what you're saying though. And I've studied some pretty extreme math in Computer Science and Astrophysics. Vranak
- I can give a concrete example of that - William Hamilton spent a large fraction of his life thinking about complex numbers (which you may recall are 'two-part numbers' having both a 'real' and an 'imaginary' part). Hamilton wondered what it would mean to have numbers with three parts instead of two. He found that three-part numbers were not very interesting - but discovered some very interesting (but entirely abstract) properties that four-part numbers have...weird - but true. These four-part numbers are called quaternions (or more rarely 'Hamiltonians' for obvious reasons). For the longest time quaternions fit Vranak's "utterly pointless" criteria. And, indeed, Hamilton was merely "Satisfying idle curiosity". OK - so fast forward about 120 years during which quaternions were more or less ignored for all practical matters. Then technologists started to represent rotations and combinations of rotations in three dimensions in the very practical fields of robotics and computer graphics. Conventionally, you'd use three angles to represent a rotation (roll, pitch and yaw) - but it turns out that this is amazingly messy - for precisely the reason that Hamilton had problems with his 'three part numbers'. Someone (I'm not sure who it was) was familiar with Hamilton's quaternions - and lo and behold, it turns out that adding a fourth number to form a quaternion results in a really elegant way to write down rotations in three dimensions - and to combine and manipulate them. That obscure and "utterly pointless" mathematical insight that Hamilton had back in the 1850's or so is now an important core principle for many computer games and for those robots you see in car plants and such. It's not at all unusual for it to take a hundred years for some piece of seemingly abstract math to become useful - but mathematicians quite often don't know in advance what will be useful and what won't - and they don't know when it'll be useful either - so they work on problems as a way of satisfying their curiosity - and years, decades or centuries later, some practical scientist or technologist will rediscover their work and make something wonderful using it. That's how mathematics is done - and we should never ever put mathematicians down for studying seemingly useless areas of their discipline. I'm no mathematician - but I surely do appreciate the work they do. SteveBaker 21:00, 15 April 2007 (UTC)
- Yeah, cars and computer games, everyone loves them. Vranak
- Actually, Vranak is correct. Most pure mathematics has no practical use (the canonical exceptions have been mentioned above, but they are few, and far between) and most pure mathematicians are motivated most of the time by idle curiosity. Hardy's A Mathematician's Apology famously justifies this stance. In a Brave New World-style dystopia, pure mathematics would be outlawed alongside art, literature and religion, as it would have no place in a purely functional society. I happen to think that the ideas behind 1 − 2 + 3 − 4 + · · · are as beautiful and elegant as Fauré's Requiem or a Canaletto, and I wouldn't want to live in a society that did not permit people to indulge in such pleasures - but that is a personal opinion, and I respect the views of those who think otherwise. Gandalf61 23:51, 15 April 2007 (UTC)
- Just because outlawing mathematics would be odious, that doesn't mean it has much value. And yes, just because I pointed this out, it doesn't make math worthless either. Vranak
I do find it ironic that Vranak is talking about a metric, that is value, and that most of mathematics does not measure up to his standards. Root4(one) 03:41, 16 April 2007 (UTC)
- Oh my god.
- Which do you think came first, conceptions of value, of worth, or people adding up numbers on an abacus? Vranak
Urea Experiment
For my senior project in high school, I recreated Wohler's Synthesis of Urea. In the reaction, lead(II) cyanate was combined with ammonia to yield ammonium cyanate which rearragned to form urea. The reaction took place in an ethanol-water mixture that was heated to 70 degrees C for 90 minutes.
I would like to go to detail in my lab report about why ammonium cyanate, an ionic compound,spontaneously rearranges to form urea, a covalent compound, and would like to prove it mathematically. I realize that the sign of ΔG must have been negative for the reaction to spontaneously occur under the given conditions. Since the reaction proceeded at high temperatures, I realize that the sign of ΔH and ΔS probably both were positive for the reaction to be spontaneous in the forward direction. My experience with gibbs free energy is limited, and all of problems I have done in class have involved gases. I was able to locate thermodynamic data for urea in the gas phase, but in my reaction the all reactants were aqueous. In addition, I couldn't find any data at all for ammonium cyanate.
I would really appreciate it if anyone could point me to a good source of data, explain to me why my book only uses gases for thermodynamics, or give other suggestions for explaining why ammonium cyanate changed to urea in my lab report. Thank you! 71.253.34.212 03:30, 15 April 2007 (UTC)purecontrol
LORAN C
how pulse and cycle matching is done in LORAN-C navigation system?thank you for any help —The preceding unsigned comment was added by Ambuj0542 (talk • contribs) 05:39, 15 April 2007 (UTC).
- Our article on LORAN might help. Splintercellguy 05:48, 15 April 2007 (UTC)
Anaerobic Respiration
CAN HUMAN BEINGS BREATHE ANAEROBICALLY FOR LONG PERIODS OF TIME? WHAT IS THE MAXIMUM TIME A NORMAL PERSON CAN BREATHE ANAROBICALLY? IF PEOPLE CAN BREATHE ANAEROBICALLY, WHY DO SOME PEOPLE STILL DROWN? —The preceding unsigned comment was added by Invisiblebug590 (talk • contribs) 06:42, 15 April 2007 (UTC).
- No, zero, and N/A. While humans are capable of anaerobic respiration, this is only to suppliment aerobic respiration in times of strenuous physical activity. It is extraordinarily less efficient than aerobic respiration, and cannot sustain a human in the absence of oxygen for any appreciable amount of time. Someguy1221 07:36, 15 April 2007 (UTC)
- Further reading here expounding on this. Anaerobic respiration can provide energy to muscles for 30 seconds to 2 minutes, but this is only in muscle cells, which might help you swim a little if you're drowning but your brain will still suffocate. Someguy1221 10:03, 15 April 2007 (UTC)
- Maybe the problem is that the inquirer is confusing anaerobic respiration (a chemical process in cells) with the act of breathing oxygen in with the lungs. alteripse 12:53, 15 April 2007 (UTC)
Dry ice safety
In our article on dry ice (actually part of the carbon dioxide article) and in other places around the web, I've seen references that dry ice is dangerous to touch because it is so cold. While dry ice is obviously pretty chilly (-78C), I think the burning danger results from it being so *dry* that it dehydrates your skin on contact. Is this correct? I can't find a source on the net, but I know from experience that if you handle CO2 with even thin gloves, it might be uncomfortably cold, but not painful if done quickly, while touching it to bare skin hurts pretty much on contact. To me, that means that it is not just temperature at work. If I am right, I'd like to find a reliable cite, so I can add it to the article. On the other hand, I'm not 100% certain that I am right, or I'd add something myself. Any help? Matt Deres 14:58, 15 April 2007 (UTC)
- It's only "dry" because solid carbon dioxide does not melt into liquid carbon dioxide. It sublimes directly into gaseous carbon dioxide. It's not dry in the sense that it contains no water.
Try touching liquid nitrogen if you want something really cold, or better yet, a piece of metal that has been cooled by liquid nitrogen. :P--Russoc4 15:12, 15 April 2007 (UTC)- (Well, it is dry in the sense that it contains no water, but you're right, that's not why it hurts, or stated another way, it doesn't hurt by dehydration, except perhaps indirectly due to freeze-drying. —Steve Summit (talk) 15:41, 15 April 2007 (UTC))
DO NOT TOUCH ANYTHING WITH YOUR BODY THAT IS BELOW THE FREEZING POINT OF WATER! Nebraska Bob 15:25, 15 April 2007 (UTC)
- Are you kidding? Do you never go outside of your (Nebraska?) house all winter for fear that you might have to touch the house's doorknob to get back in? Obviously, it's a good idea not to touch something that's below freezing and thermally massive if your skin is wet, especially if your name is Flick, but your blanket bold-faced prohibition is just plain silly. Well, unless conditions in Nebraska are a lot different than New Hampshire. ;-)
- Nope; it's just the cold that does it. Even thin gloves provide some insulation, which is vastly superior to no insulation. If you try touching something like bare metal that has been chilled with dry ice (or which comes straight from an ultralow freezer), you'll note that you get the same pain that you get from direct contact with dry ice. (I just use a double pair of latex or nitrile gloves if I need to do more than a few seconds of work in a -80 freezer; they give sufficient insulation while still leaving me some manual dexterity, but you do have to be wary of frostnip if you're going to do more than a few minutes of work.) TenOfAllTrades(talk) 15:34, 15 April 2007 (UTC)
- I have struck out User:Russoc4's
stupidly dangeroussuggestion. It is idiotic to say things like that on a public web page when our readers may not realise you are making some kind of joke (which isn't funny in any way). Liquid Nitrogen is at -195C - much, much colder than solid CO2 and it would be exceedingly dangerous to touch it - or a chunk of metal cooled by it. SteveBaker 15:36, 15 April 2007 (UTC)- In fairness, I think "stupidly dangerous" and "idiotic" are a little strong. It was a borderline comment, to be sure, but really: how many readers won't realize that in that context, the word "try" basically means "imagine"? (Of those readers, how many would be moved to actually try it? And of those, how many would have access to liquid nitrogen?) —Steve Summit (talk) 15:46, 15 April 2007 (UTC)
- I don't know - and for sure I don't recommend "the experimental approach" to finding that out. When it comes to safety matters we should have a zero tolerance policy for dumb advice...made jokingly or not. SteveBaker 20:39, 15 April 2007 (UTC)
- Well at least s/he didn't recommend liquid helium. I agree with you though. There is easily the risk a child (who shouldn't have access to liquid nitrogen but I digress) or someone with only a rudimentary understanding of English may misunderstand that Nil Einne 23:16, 15 April 2007 (UTC)
- I don't know - and for sure I don't recommend "the experimental approach" to finding that out. When it comes to safety matters we should have a zero tolerance policy for dumb advice...made jokingly or not. SteveBaker 20:39, 15 April 2007 (UTC)
- Oddly enough, touching liquid nitrogen – at least for modest lengths of time – isn't all that bad. I've done it a number of times, and it's the sort of demonstration that old physics profs (from the era before everything had a warning label) relish. When you immerse your hand in LN2, the liquid in contact with your hand boils immediately, surrounding your hand with a layer if nitrogen gas. The gas is a pretty good insulator that mostly protects your hand from contact with the rest of the very cold liquid. (This is a similar phenomenon to a water droplet 'dancing' on a very hot griddle. The layer of steam under the droplet insulates the rest of the droplet, keeping it from boiling off for an extended period of time.)
- On the other hand, if you touch something that has been chilled with liquid nitrogen but that won't boil in contact with your skin, heat will be transferred out of your hand very quickly and will potentially cause rapid injury. TenOfAllTrades(talk) 16:02, 15 April 2007 (UTC)
- In fairness, I think "stupidly dangerous" and "idiotic" are a little strong. It was a borderline comment, to be sure, but really: how many readers won't realize that in that context, the word "try" basically means "imagine"? (Of those readers, how many would be moved to actually try it? And of those, how many would have access to liquid nitrogen?) —Steve Summit (talk) 15:46, 15 April 2007 (UTC)
- I have struck out User:Russoc4's
- Things that are extremely cold (or hot) are dangerous due to the combination of their temperature and heat capacity. If something is at an extreme temperature, but has either tiny mass or a low specific heat, touching it won't hurt very much. (That's why you can get showered with sparks, from say a grinder or a sparkler, without injury, even though those sparks are basically flaming metal.)
- But dry ice obviously does have a decently high heat capacity (otherwise we wouldn't be using it for cooling things).
- If you had a piece of aerogel, or a space shuttle thermal tile, at -78°F, you could probably hold it in your bare hand without injury. —Steve Summit (talk) 15:37, 15 April 2007 (UTC) [P.S.: Probably! I'm speculating here; I really don't know for sure. "Don't try this at home, kids!"]
- it was just a joke. Actually, I meant to say "try touching liquid nitrogen if you want... to feel something cold, but I lost my train of thought and left it out. Also, one of my chemistry professors put it in his mouth! It's not like it instantly kills you. Yes, it's damn cold, but it's no more dangerous than accidentally touching a hot pot on a stove. I'm sorry if I offended you, or the reference desk. —The preceding unsigned comment was added by Russoc4 (talk • contribs) 16:17, 15 April 2007 (UTC).
- What? Stealing a tile from the space shuttle, putting it in a refrigerator at -78 C, and holding it in your hands? That's something every kid has the resources to do! --Bowlhover 16:20, 15 April 2007 (UTC)
- It's not that hard. Just wait for one to fall off (they do it all the time) and use the liquid nitrogen that was mentioned 23:20, 15 April 2007 (UTC)
- Hmmm. I think this thread needs some reliable sources. Goggling "liquid nitrogen" and "safety" turns up these safety notes on Liquid Nitrogen Demonstrations from the University of Wichita, which say:
- Teachers must stress to their students the importance of not touching frozen objects or nitrogen.
- Wear goggles whenever pouring or dumping nitrogen. Nitrogen can spatter into the eyes, and potentially blinding pieces of frozen things can fly around when we drop it.
- Use a glove and / or tongs to handle any object going into or out of nitrogen and to carry the nitrogen dewar. Gandalf61 16:47, 15 April 2007 (UTC)
I believe there is a knack to bare-handed handling of dry ice without getting hurt. It involves tossing the ice from hand to hand so that it doesn't have time to freeze any particular spot of skin. This information comes with absolutely no warranty -- I wouldn't be able to tell you how often you have to toss the ice, or whether you'll get hurt when you pick it up the first time, or anything like that, so don't come crying to me if you try it and get burned. --Trovatore 19:10, 15 April 2007 (UTC)
Thanks for the answers, everyone. We've kind of drifted a bit, but that a-okay, too. My hypothesis that dry ice essentially did a freeze drying job on your skin seems to have been an error. Checking out that article, I see that dry ice is used for that purpose, but apparently only as a cooling agent. Matt Deres 19:59, 15 April 2007 (UTC)
Hmm, well, as long as we answered your question. The point I tried to make with the liquid nitrogen is that dry ice is not that cold. You can touch it, just like you can touch regular ice made of water. If you handle it for too long, it starts to "burn", also just like regular ice. As Trovatore said, yes, you can handle it if you don't hold it for too long. The same goes for liquid nitrogen. This is how my professor puts it in his mouth, but keeping it moving around. Trust me though, neither dry ice nor liquid nitrogen are anymore dangerous than a pot of boiling water. You're natural reflexes will keep you from getting burned, and if you do, it doesn't cause serious damage. In fact, I think a burn from a pot of water hurts more, and last longer than a liquid nitrogen burn, which for me lasted minutes. --Russoc4 20:03, 15 April 2007 (UTC)
Please do not put casual references on Ref Desk to putting liquid nitrogen in the mouth, because the results could be fatal. And touching hot pans on the stove can obviously result in painful burns. Edison 20:04, 15 April 2007 (UTC)
- “We should be careful to get out of an experience only the wisdom that is in it—and stop there; lest we be like the cat that sits down on a hot stove-lid. She will never sit down on a hot stove-lid again—and that is well; but also she will never sit down on a cold one any more.”[1] —Mark Twain —The preceding unsigned comment was added by Ummit (talk • contribs) 20:42, 15 April 2007 (UTC).
Just to interject here, liquid nitrogen is not instantly fatal, and routinely physics professors slosh some around in their mouth during those great cyrogen demonstrations. [Mαc Δαvιs] ❖ 20:34, 15 April 2007 (UTC)
- Thank you Mac Davis. --Russoc4 21:14, 15 April 2007 (UTC)
- The common exaggerations of the dangers of liquid nitrogen withstanding, I'd like to share an anecodote as a counterpoint to some of the comments here. When I started my PhD at a research institute a number of years ago, my new lab-bench was next to an experienced technician's. On my 5th day in my new lab - having just got to know my new colleague - he went downstairs by himself to decant some liquid nitrogen for the lab. Exactly what happened next was never clarified, but he was found dead in a rapidly evapourating pool of liquid nitrogen just a few minutes later (and a few other lab members were injured trying to rescue him). This was a man who had been working with liquid nitrogen on a weekly basis for years. Just thought I'd add that to the mix to illustrate it, like dry ice, should be dealt with with the utmost care. Oh and here is a reference, incase anyone thinks this is a scare story. [2] —The preceding unsigned comment was added by Rockpocket (talk • contribs) 23:52, 15 April 2007 (UTC).
- That's very unfortunate for him, and it does show the capabilities of liquid nitrogen, but every job has its risks. Things malfunction and accidents do happen everywhere. --Russoc4 00:27, 16 April 2007 (UTC)
- I would guess he had suffocated from lack of oxygen. If you're breathing nitrogen gas you won't feel like you are out of breath, but you will still be dying. He could easily have gotten light headed and fallen over, knocking the LN2 dewar next to or on him. Of course I wasn't there and don't know what happened, but I don't think he froze to death. Simply put it is a substance that has many properties that we are not accustomed to, and don't encounter them in every day life. The temperature, the rapid evaporation, the potential for explosion, and more. [Mαc Δαvιs] ❖ 03:14, 16 April 2007 (UTC)
- I'll echo what's been said above. The biggest risks associated with handling liquid nitrogen aren't from the cold liquid itself. (Though I'd tend to shy away from the 'sloshing it around in your mouth' demo, as inadvertently swallowing some – hiccup! – could have very unpleasant sequalae.) For milder injuries, you're looking at contact with uninsulated surfaces (particularly metallic ones) that have been chilled with liquid nitrogen. There's a risk of frostbite, and a risk of injury if you freeze your skin to a surface. For the most serious injuries (and deaths), you're looking at the effects of hypoxia, when nitrogen dilutes or displaces oxygen from the air in a confined space. Straight oxygen starvation can do you in; there's also the risk of serious injury when you lose consciousness and fall.
- Any workplace that handles liquid nitrogen needs to provide appropriate training that addresses these risks. About a liter and a half of liquid nitrogen will boil off to form a full cubic meter of gas; LN2 should never be dispensed or transferred in a small or poorly-ventilated space. Note that many workplaces ban the transportation of liquid nitrogen containers in occupied passenger elevators for these reasons. TenOfAllTrades(talk) 03:34, 16 April 2007 (UTC)
Epoxy aroma
What makes the aroma of epoxy and polyester resin so pleasant and are the epoxies and resins with putrid smell yet perhaps with superior characteristics (heat tollerance, bonding strengh, etc.? Nebraska Bob 15:23, 15 April 2007 (UTC)
- Probably Aromatic hydrocarbon may help. These chemicals might be present in some quantity in various epoxies. Nimur 16:50, 18 April 2007 (UTC)
Alternating Current
Very simple and very basic question: What happens to the electrons in a conductor when an alternating current is passed through it? I'm interested in the displacement of electrons. (In DC, elecrons move from A to B). =Nichalp «Talk»= 15:54, 15 April 2007 (UTC)
- Well they move back and forth basically. For a typical wire the speed is very low, centimeters per second at best. —The preceding unsigned comment was added by 84.187.46.16 (talk) 16:22, 15 April 2007 (UTC).
- Heres a nice link [3] explaining it simply. After the simple explanation it gets quite contoversial. Basically the speed of the electricity is the speed of light, but the 'electrons' move quite slowly. —The preceding unsigned comment was added by 88.111.3.93 (talk) 16:28, 15 April 2007 (UTC).
- Think of it like sound moving through air. The sound moves very quickly, while the air usually moves much slower. StuRat 19:14, 15 April 2007 (UTC)
I dont think that's a good anlaogy StuRat. The compression wave and therefore the air molecules move at exactly the speed of sound in the medium. Sound is a longitudinal wave and that the above must be so is obvious. —Preceding unsigned comment added by 88.111.3.93 (talk • contribs) 19:21, 15 April 2007
- The speed of individual electrons as they jump from one atom to another is quite high, as well, but nonetheless, the average speed of all the electrons through which electrical current passes, just like the average speed of all the air molecules through which a sound wave passes, is quite low. StuRat 19:29, 15 April 2007 (UTC)
- You miss the point in that electromagnetic energy is a transverse wave phenomenon where the speed of propagation is not limited by the velocity of the individual particles 'causing' it! —Preceding unsigned comment added by 88.111.3.93 (talk • contribs) 19:35, 15 April 2007
- Neither are compression waves. Think of a long tube filled with tennis balls. You stick one in on one end; the last one pops out the other end. If you divide the length of the tube by the time needed for the last ball to pop out, you can see that the compression wave must have moved much faster than any individual ball. --Trovatore 19:38, 15 April 2007 (UTC)
- No faster than the parts of the tennis balls touching each other! —Preceding unsigned comment added by 88.111.3.93 (talk • contribs) 19:40, 15 April 2007
- I'm sorry, you're simply wrong. The compression wave does move faster than the parts of the tennis balls touching each other. --Trovatore 19:43, 15 April 2007 (UTC)
- No faster than the parts of the tennis balls touching each other! —Preceding unsigned comment added by 88.111.3.93 (talk • contribs) 19:40, 15 April 2007
- Neither are compression waves. Think of a long tube filled with tennis balls. You stick one in on one end; the last one pops out the other end. If you divide the length of the tube by the time needed for the last ball to pop out, you can see that the compression wave must have moved much faster than any individual ball. --Trovatore 19:38, 15 April 2007 (UTC)
- Even at the molecular level? Care to explain how? —Preceding unsigned comment added by 88.111.3.93 (talk • contribs) 19:45, 15 April 2007
- You're positing a difference in the propagation speed of longitudinal waves versus compression waves, or a difference between the relationship of one of those waves to some "speed" of the medium across they propagate, versus the other one. Care to explain what you mean, and what it is that "must be obvious"? (And could you please sign your posts?) —Steve Summit (talk) 19:53, 15 April 2007 (UTC)
- Thers no difference according to those links you quoted!--88.111.3.93 20:16, 15 April 2007 (UTC)
- You're positing a difference in the propagation speed of longitudinal waves versus compression waves, or a difference between the relationship of one of those waves to some "speed" of the medium across they propagate, versus the other one. Care to explain what you mean, and what it is that "must be obvious"? (And could you please sign your posts?) —Steve Summit (talk) 19:53, 15 April 2007 (UTC)
- (Edit conflict, to the anont). If you want to go down to the very lowest level, the forces are transmitted by the exchange of field quanta, which in the case of the relevant force (electromagnetic) are photons. They move at the speed of light. So if you insist on this point, the "parts of the tennis balls touching each other" are actually moving at the speed of light, and of course the compression wave doesn't travel faster than that. But that's not a normal way of understanding the phrase "the parts of the tennis balls touching each other". --Trovatore 19:53, 15 April 2007 (UTC)
- So the compression wave travels at the speed of light? Even though you insert the balls at less than c? Thats clever!.--88.111.3.93 20:08, 15 April 2007 (UTC)
- I would have thought that the compression wave would travel at the speed of sound in the medium (rubber or whatever theyre made of these days). Is that not correct? —The preceding unsigned comment was added by 88.111.93.55 (talk) 23:09, 15 April 2007 (UTC).
- Well, more or less -- the compression wave is sound, in a sense. No, it doesn't travel at the speed of light. The field quanta that transmit the force travel at the speed of light, but the wave travels much slower. I don't know where you got the idea that the compression wave has to travel at the same speed as the particles, but in any case, that idea is completely wrong. Where you do have a point, sort of, is that it can't travel faster than the force can be transmitted, and that speed is limited by the speed of the field quanta. --Trovatore 01:14, 16 April 2007 (UTC)
- I would have thought that the compression wave would travel at the speed of sound in the medium (rubber or whatever theyre made of these days). Is that not correct? —The preceding unsigned comment was added by 88.111.93.55 (talk) 23:09, 15 April 2007 (UTC).
- Or imagine a long pipe filled with water, with a faucet in (say) your bathroom, and a water heater in the basement. If you turn on or off the bathroom faucet (or if I turn on or off the shut-off valve in the basement), the flow starts or stops immediately. Yet (as everyone has experienced) it can take quite a while for the hot water to get there. —Steve Summit (talk) 19:46, 15 April 2007 (UTC)
- There's a separate issue there, though. Some of the cold water you feel in the shower was actually hot at the moment you turned on the faucet. It got cold on the way. In doing so, it heated up the pipes, and it's not until the pipes are hot that you get hot water at the shower head. --Trovatore 19:48, 15 April 2007 (UTC)
- Yeah. Is that at all pertinent to the current discussion? —The preceding unsigned comment was added by 88.110.218.16 (talk) 20:44, 15 April 2007 (UTC).
- There's a separate issue there, though. Some of the cold water you feel in the shower was actually hot at the moment you turned on the faucet. It got cold on the way. In doing so, it heated up the pipes, and it's not until the pipes are hot that you get hot water at the shower head. --Trovatore 19:48, 15 April 2007 (UTC)
I question the claim that electron drift through a conductor carrying alternating current is a transverse wave. The electrons go back and forth (longitudinally), not transversely. Make the AC frequency low enough and the waveform is indistinguishable in any short portion from slowly varying DC. If we make the AC frequency low enough, the conductor short enough and small enough in diameter, and the current high enough, the population of electrons in the conductor can move entirely out of it and be replaced in each half cycle. It is as longitudinal as water flowing through a pipe. In normal real-wporld AC applications, the power cord is long enough and large enough in cross section, and the current is low enough and the frequency high enough that the drift rate is very slow and the same old electrons drift back and forth in the power cord never going more than a few millimeters or centimeters in an average cycle. Edison 19:55, 15 April 2007 (UTC)
- I didnt say electron dirft was transverse. I said the energy wave (electromagnetic) was transverse.--88.111.3.93 20:08, 15 April 2007 (UTC)
- A good analogy for understanding the speed of electron flow would be a 10 foot length of pipe filled with ball bearings. The pipe is the wire, the ballbearings are the free electrons. If you roll a ballbearing down an empty pipe, it might maybe take a second to come out the other end, but if the pipe is full of ballbearings and you push one in one end, a different one drops out of the far end almost immediately. Hence, the speed of an individual electron can be quite slow while the fact of the presence of an electron at one end of the wire can travel to the far end at the speed of light. In A/C current, the electrons simply drift back and forth along the wire - moving very small distances indeed. SteveBaker 20:35, 15 April 2007 (UTC)
- No its not a good analogy. You are again talking longitudinal/compression waves. Electricity is a transverse wave phenomenon as every schoolboy knows. —The preceding unsigned comment was added by 88.110.218.16 (talk) 20:38, 15 April 2007 (UTC).
- So which kind of wave is a current of light? —Steve Summit (talk) 21:34, 15 April 2007 (UTC)
- As far as I know photons do not possess charge in the conventional sense and therefore their flow cannot be considered an electrical current. What you propose (ie light current) must therefore be an
enigma(oxy)moron. Light is obviously full of energy and can illuminate things. Current on the other hand is a flow of charge that cannot be stopped in the conventional sense. Light is a transverse (or orthogonal) wave. Electromagnetic energy is a transverse wave. Hope that clears that up! —The preceding unsigned comment was added by 88.110.101.245 (talk) 21:54, 15 April 2007 (UTC).- Mm... Electrical current can be stopped. -- mattb
@ 2007-04-15T22:18Z
- Mm... Electrical current can be stopped. -- mattb
- As far as I know photons do not possess charge in the conventional sense and therefore their flow cannot be considered an electrical current. What you propose (ie light current) must therefore be an
- Hmmm! But can anything stop Light current/ I think not 8-)) —The preceding unsigned comment was added by 88.109.192.18 (talk) 22:29, 15 April 2007 (UTC).
- Not mere ban hammers... Nope. -- mattb
@ 2007-04-15T23:42Z
- Not mere ban hammers... Nope. -- mattb
- You know, there's a bit of difference between a photonic electromagnetic wave and an electrical signal in a conductor. They are related phenomena, but they aren't precisely the same. The classical compression wave-like response to electric field isn't all that far off. There are actually several conduction mechanisms, but the descriptions presented are pretty accurate for a simple conductor. Perhaps that's where the schoolboy might get confused. -- mattb
@ 2007-04-15T21:23Z
- You know, there's a bit of difference between a photonic electromagnetic wave and an electrical signal in a conductor. They are related phenomena, but they aren't precisely the same. The classical compression wave-like response to electric field isn't all that far off. There are actually several conduction mechanisms, but the descriptions presented are pretty accurate for a simple conductor. Perhaps that's where the schoolboy might get confused. -- mattb
- Im not totally sure about this, but it would appear that the wave equations for travelling waves seem to be of similar form for both compresion wave and electromagnetic waves. In neither case, does the velocity of propagation relate to the particle velocity (as far as I can understand) but relates purely to the medium constants: density/stiffness of the air, or permeability/permittivity of free space.
- Maybe the relevant articles should try to explain the travelling wave phenomenon (for the case of compression waves, say) more clearly so that people like me get a deeper understanding of how it works? ie how exactly can something fast (the wave disturbnce) actually be caused by something slower (or even faster) than itself? Or am I being incredibly dense?--88.109.136.82 12:35, 16 April 2007 (UTC)
- Please do not try to discuss the details of electron movement in a conductor with classical physics. If you are interested the in details, take a look at "Feynmans Lectures on Physics, Quantum Mechanics, Propagation in a Crystal Lattice", it gives a nice introduction on electron movement in a metal. —The preceding unsigned comment was added by 84.187.32.191 (talk) 20:21, 17 April 2007 (UTC).
higher Coefficient of relationship
Is it possible for a parent, sibling, cousin or anyone to have a higher Coefficient of relationship to you than your offspring? Clem 16:52, 15 April 2007 (UTC)
- Presumably your clone would. --TotoBaggins 18:05, 15 April 2007 (UTC)
Yes. Children of completely unrelated parents (meaning no common chromosomes, in this example) should always have exactly half of each parent's chromosomes. Full siblings of unrelated parents have, on average, one half their chromosomes in common (neglecting identical twins, triplets, etc.), but this can vary from no chromosomes in common to all chromosomes in common. Thus, the chances that siblings who are not identical will have more than half their chromosomes in common is only slightly less than half (because there is some chance they have exactly half their chromosomes in common). Identical twins, triplets, etc., always have all their chromosomes in common. First cousins only have one quarter of their chromosomes in common, on average, so it would be less likely that they would have more than half their chromosomes in common, but still possible. StuRat 19:09, 15 April 2007 (UTC)
- The process that StuRat refers to does not happen at the chromosomal level. Each of your autosomal chromosomes is a patchwork of stretches from one of your parents' paternal and maternal chromosomes. See Chromosomal crossover and Meiosis. This also applies to the X-chromosome, girls inherit a patchwork of parts from their mother's maternal and paternal X-chromosomes. I'm not 100% certain about whether there may be "autosomal" parts of the Y chromosome that can cross over with corresponding parts of the X chromosome. If we assume there isn't, boys inherit the entire Y-chromosome from their father, and girls inherit the entire X-chromosome of their father. Both boys and girls inherit their mitochondrial DNA from their mother. --NorwegianBlue talk 19:41, 15 April 2007 (UTC)
Is then the Coefficient of relationship the most realistic biological means for distributing wealth and/or possessions for someone who has died without leaving a will rather than for all of their wealth and/or possessions to become the property of the state? Clem 20:00, 15 April 2007 (UTC)
- That's entirely a societal question, not one that can be answered by science. StuRat 20:19, 15 April 2007 (UTC)
- To clarify, it is a societal question StuRat but one which is intended to expose the strength/weakness or applicability/reliability of such a measure as the COR as answered below. Clem 22:22, 15 April 2007 (UTC)
- (edit conflict)
- This is a matter of legislation, not biology. Your question rests on the premise that the money should follow the genes. Where I live, there is no distinction between adoptive children and biological children in such matters, but this may vary from country to country. Such a system would easily lead to unreasonable consequences. For instance, it would imply that cousins whose fathers are identical twins should inherit an equal share of the estate of each twin. --NorwegianBlue talk 20:24, 15 April 2007 (UTC)
- Although indeed a social and legislative issue this is possibly one of the areas in which science/mathematics could help provide a fair and reasonable basis for distribution of assets in the absence of a will but mainly here I am wanting to expose the weaknesses/strengths and applicability/reliability of the measure since this it is assumed to be quit suitable for biological purposes such as organ donation. "...so you're asking me to give up a kidney since we are biologically related but yet have not for the same reason included me in your will?" Clem 22:46, 15 April 2007 (UTC)
- The reason its used in organ transplants is not as a justification for donation, but for medical reasons. The greater your COR is to the donor, the smaller the chance that the organ will be rejected. This is the same reason we wish to develop theraputic cloning, because growing a new organ with your own DNA is the equivilent of getting an organ from a clone of you (a COR = 1).
- If one could SNP map an entire human genome at a reasonable cost, one could determine roughly the proportion of DNA shared between the person who died and the potential benefactors of their will. So it could be done. But even the most strict believers in genetic determinism would find it difficult to justify why having an extra 3% of your grandfathers alleles compared to your sibling would be good cause to distribute wealth his wealth accordingly. For example, say the person with the extra 3% of the grandfather's alleles had an excess of his recessive alleles, while the person with less of grandfather's DNA in total, had a lot more dominant alleles. That would mean the person with the less DNA could be phenotypically much more like their grandfather than their sibling. Rockpocket 02:18, 16 April 2007 (UTC)
- The answer to that would of course be deferred to and ultimately determined by the Genetic Determinism Legislature and Judiciary since it is a social/legal issue! The science would simply provide a foundation or backbone, if you will, upon which to make such decisions. Clem 04:10, 16 April 2007 (UTC)
- Since many families have adopted children to link inheritance of wealth to geneotype would not be useful for all cases. David D. (Talk) 18:00, 16 April 2007 (UTC)
- The answer to that would of course be deferred to and ultimately determined by the Genetic Determinism Legislature and Judiciary since it is a social/legal issue! The science would simply provide a foundation or backbone, if you will, upon which to make such decisions. Clem 04:10, 16 April 2007 (UTC)
Nitric Acid
This is random, but I'm working on a mechanism for the oxidation of benzoin using only nitric acid, and it's annoying the hell out of me. Anyway, I'm not sure why I haven't thought of this before, but does the proton-less oxygen of nitric acid not pick up another proton, but rather it looses a proton from the OH. --Russoc4 19:01, 15 April 2007 (UTC)
- I believe you are correct. If I remember correctly, the nitrogen and other oxygens draw the electrons away from the bond between the hydrogen and oxygen, more or less leaving the hydrogen dangling, ripe for the picking by a base. It appears to be possible to protonate nitric acid, but it takes a really really strong acid (H3 or CH5? wacky.) [4]--Bennybp 04:11, 16 April 2007 (UTC)
- Probably two important effects here. The formally positively charged nitrogen is likely important in attracting electrons from the oxygen atoms (less likely to reach out for H+ away from N+): compare the acidities of nitric acid and nitrous acid. Also, lone pairs on each of the singly-bonded oxygens are resonance-stabilized, rendering them less basic (or the protonated form of them more acidic). The nitric-acid oxidation of benzoin to benzil was promoted by adding additional acid, so presumably further protonation of HNO3 (or at least keeping nitric acid in its protonated form instead of as nitrate anion) is important to the mechanism, but last I knew the mechanism was not completely established or straightforward. DMacks 19:05, 16 April 2007 (UTC)
Passive immunity
Durring passive imunity your white blood cells still build up some ammount of active immunity?Bastard Soap 19:38, 15 April 2007 (UTC)
- Often yes. Functional immune cells may still respond to novel antigenic protein even when there are antibodies from other sources present. alteripse 19:57, 15 April 2007 (UTC)
- That's true, but just to be clear: active immunity doesn't build up in response to the passive immunity. --David Iberri (talk) 14:14, 16 April 2007 (UTC)
Wrong Article
When searching for gauss rifle, you get the article about coilguns. They are not the same. How can i make an article about gauss guns specifically? —The preceding unsigned comment was added by Dansportman (talk • contribs) 20:00, 15 April 2007 (UTC).
- Replace the redirect with your new article. 71.100.175.14 20:03, 15 April 2007 (UTC)
- The article coilgun says that a gauss gun uses electromagnets while a coilgun uses solenoids. The article railgun claims that coil guns and gauss guns are similar, but both different from a railgun. If you want to access the pages that redirect to coilgun, see this this page, however, I don't know if a change is necessary.
- It's common for us to have a redirect to something similar, and then, within that article, explain the differences. StuRat 20:15, 15 April 2007 (UTC)
Don't worry guys, it's the questioner that is wrong. What is known as a "guass gun" is exactly the same as a "coil gun." Guass/coil guns use coils and rail guns use rails. [Mαc Δαvιs] ❖ 20:34, 15 April 2007 (UTC)
Solenoid is type of electromagnet. -Yyy 06:46, 16 April 2007 (UTC)
Unknown Dianthus Image
I took a nice photograph of a dianthus flower. Can the genus be identified so that the image can be placed in an appropriate article? Your help is much appreciated. Thegreenj 22:37, 15 April 2007 (UTC)
- Where did you take the pic? bibliomaniac15 00:19, 16 April 2007 (UTC)
- I am not sure, but I believe that it was taken a trip to Tennessee. Thegreenj 22:32, 16 April 2007 (UTC)
- It looks very similar to Dianthus plumarius, or the wild pink carnation. The picture on the dianthus article looks very similar to yours, only crappier. bibliomaniac15 00:39, 17 April 2007 (UTC)
- Can you say for sure that it is a Dianthus plumarius and not a Dianthus gratianopolitanus, which is also brought up by a web searh for the word dianthus. If you know the difference and can positively identify it one was or another, your help is still welcome... Thank you so far - Thegreenj 01:23, 17 April 2007 (UTC)
- I have identified it as a Dianthus plumarius. Thank you for your help. Thegreenj 20:05, 17 April 2007 (UTC)
Sit-ups
I always see overweight people doing sit-ups, and I wonder why, is there a reason to do them if you dont have a flat stomach? Because I know you cannot just lose fat from one area of the body —The preceding unsigned comment was added by 76.167.136.84 (talk) 22:47, 15 April 2007 (UTC).
- Situps are good for reducing lower back pain. Fat people tend to have lower back pain. I just wonder where you are seeing fat people doing excercise. I work in a hospital and I see fat people in the elevator, riding the courtesy tram, getting pushed around in wheelchairs - basically anything to avoid excercise before they see the doctor to find out how bad their hypertension, hypercholesterolemia, and diabetes is getting. --Kainaw (talk) 22:54, 15 April 2007 (UTC)
- Just because one cannot lose fat from a specific part, does not mean that one cannot gain muscle in a specific part. Situps are one way (though there are other, arguably more effective methods) of strengthening core muscles, which help us, among other things, avoid back injury, improve posture, and maintain (mechanical) balance. tucker/rekcut 00:25, 16 April 2007 (UTC)
April 16
Total number of people
What is the total number of people to have ever lived and how many people die and are born each year? 71.100.175.14 04:01, 16 April 2007 (UTC)
- I don't know off the top of my head, but I just typed "total number of people to have ever lived" into Google, and the first lotsa hits look relevant... —Steve Summit (talk) 04:03, 16 April 2007 (UTC)
- The first question has been asked several times recently. Estimates vary of course, but somewhere in the region of 100 billion, as I recall. Clarityfiend 04:31, 16 April 2007 (UTC)
- No need to recall or guess. It's all here, in our very own Wikipedia. JackofOz 04:45, 16 April 2007 (UTC)
- See
- Wikipedia reference desk Science Archive September 2006
- How many humans have ever lived.
- http://en.wikipedia.org/wiki/Wikipedia:Reference_desk_archive/Science/2006_September_27
202.168.50.40 05:15, 16 April 2007 (UTC)
Reason for asking:
From the above and according to Ramsey at the Department of Mathematics at the University of Hawaii so long as the total number of people that have ever lived (have been born) is less than 781,250,000,000 only Seven Degrees of Separation are required to link every single human who ever lived assuming that each person still knows at least 50 other people. Drop that number to 5 contacts and the Degrees of Separation only jumps to 16. 71.100.175.14 06:51, 16 April 2007 (UTC)
- There must be additional assumptions. I believe that figure would only be true if those fifty people are essentially distributed at random around the world. Take an extreme case: an isolated island with 51 people, where everyone knows everyone else, but has never met anyone not from the island. Each one of those islanders knows fifty people, yet you could trace through as many degrees as you would like and they would never be connected to you, for instance. In reality, contacts tend to be clustered around geographic connections (and to a lesser extent, cultural, professional, and so on). — Knowledge Seeker দ 08:52, 16 April 2007 (UTC)
- Aren't you forgetting something? Those people had to have come from somewhere and it is the link with the people from which they came that links them to everyone else when you include previous living persons. 71.100.175.14 22:01, 16 April 2007 (UTC)
- Of course, that's a gross oversimplification; the seven degrees of separation calculation is not – I'm sure – meant to be taken literally. If we take the maximum human lifetime to be of the order of 120 years, with seven degrees of separation there's no way to be linked to anyone from more than 840 years ago.... TenOfAllTrades(talk) 12:55, 16 April 2007 (UTC)
- Did you actually do the math? The estimated total number of humans ever born going back a million years based on only an average 25 year life span falls well within Seven Degrees of Separation with 50 contacts per degree. 71.100.175.14 21:42, 16 April 2007 (UTC)
- Er, how do you have a contact with someone who died before you were born? TenOfAllTrades(talk) 22:18, 16 April 2007 (UTC)
- By simply specifying that your application of DoS is not limited to the living but also included the dead just as you can specify that you have a hereditary relationship with your great, great, great, great, great grandmother who I am assuming is no longer living. 71.100.175.14 22:43, 16 April 2007 (UTC)
- By that token, any living creature can be connected to any other living creature with only two degrees of separation, via the universal common ancestor... SamSim 19:52, 19 April 2007 (UTC)
The total number of people who have ever existed is probably between 70000000000 and 100000000000. There are estimated to be around 4 deaths and 6 births each second, whch is about 125000000 and 190000000 each year. But of course these are all estimates, especially since people disagree on how long humans have existed for.
Do certain squirrel species commit suicide? (or for that reason any species, other than the human species?
I am researching on the subject of suicide. Currently wondering if there are other species (alive or extinct) that are capable of committing suicide. I've searched google, but instead landed up in blogs that describe how squirrels cross the road and get killed...or something like that. Are animals or insects as such capable of bringing an end to their own life?Arun T Jayapal 09:32, 16 April 2007 (UTC)
- I don't know of any animals besides humans who commit suicide for the pure sake of ending their lives, but bees die when they sting something (sacrifice themselves to scare away what might threaten the hive), deer stare stupidly at headlights and get run over instead of stepping aside (what is that, fear? Confusion? I'm not sure actually). And, of course, there are always wonderful, cute, tiny, suicidal lemmings (mythically suicidal at least, they don't actually mean to kill themselves). But squirrels? I'm willing to be they're just dumb. I say don't worry if you run one over, do your part to help natural selection ;-) Someguy1221 10:07, 16 April 2007 (UTC)
- I believe deer are exhibiting an inappropriate survival response to "freeze" so the "predator" (car) won't see them. Nothing in their evolution prepared them for dealing with cars, so they react to them like they would to a predator they know they can't outrun. If that was actually the case, freezing and hoping the predator doesn't detect them would indeed be their best chance at survival. StuRat 14:48, 16 April 2007 (UTC)
- Possibly related to this is Learned helplessness, which shows that at least animals can learn some sense of futility. The basic experiment taught dogs (through conditioning) that the sound of a bell would be followed by an electric shock. Dogs that had a means of escape from the start would quickly learn to use it when the signal was given. Dogs that did not have this possibility of escape during learning would not not use it when it was introduced later on. In this way an animal could at least commit suicide through inaction, rather than action. A lot of behavior surrounding learned helplessness seems to correlate to human concepts like clinical depression and optimism, which suggests that animals can at least suffer suicidal emotions, even if they are unaware that death might stop the pain. risk 22:25, 16 April 2007 (UTC)
- It's the same with hedgehogs and cars. They roll into a ball for protection when they see the headlights - which is not much use vs. a wheel. I think it's the same with armadillos - maybe one of the Americans here can confirm that they are regular roadkill victims (I think I read that). --Kurt Shaped Box 22:30, 16 April 2007 (UTC)
- Hmm. Why do bees die after they sting?Arun T Jayapal 13:06, 16 April 2007 (UTC)
- Bees die after they sting because the stinger is barbed in order to remain lodged in the skin of the victim when the bee flys away, and when the stinger pulls out, the venom glands come with it in order to continue pumping venom into the victim. This removal of the stinger / venom gland results in a mortal wound for the individual bee. This is a classic case of Altruism in the evolutionary sense. -Czmtzc 14:02, 16 April 2007 (UTC)
- That definetly qualifies as a suicide.
—The preceding unsigned comment was added by 84.187.59.188 (talk) 23:08, 16 April 2007 (UTC).
- If you mean do healthy animals commit suicide, I think the answer is no. But this would depend on if they knew their actions would result in death. Do animals have a sence of life and understand that they may die at some point - and if they do, do they click that they could end their own life sooner? But there are cases where sick animals will do things that cause them to die faster, like an indured whale beaching itself for exapmple. I think that somewhere along the line its happened, but don't know if you'll find much info on it. Think outside the box 11:29, 16 April 2007 (UTC)
My dog acctually commited suicide after its pups were born. we paid more attention to the puppys (but still kept spoiling him) but he wanted all the attention so one day he just looked at us then ran straight into the tires of a incomming car. now before you say anything this dog was smart he knew what cars did and he would never go near the road for this reason. this is why i belive that he committed suicide that day its the only explanation for his actions =( User:Maverick423 If It Looks Good Nuke It 13:50, 16 April 2007 (UTC)
- I wonder if dogs ever suffer from post-partum depression ? StuRat 14:54, 16 April 2007 (UTC)
As for suicidal animals, there are many species that die after they have "served their purpose" (usually mating for males and giving birth/laying eggs for females), however, this is typically accomplished by some biological mechanism (not well understood) other than intentional suicide. Knowing whether you are a net help or hindrance to your relatives is complicated, so requires a fair amount of intelligence to determine. This may be why the decision of when or if to commit suicide isn't left up to less intelligent animals. I can think of one possible exception. I believe in many species a sick individual will leave the group and "go off to die". This death will then take place due to predation, starvation, dehydration, exposure, etc. StuRat 15:02, 16 April 2007 (UTC)
You know i acctually seen that in many documentrys of animals. when a preditor can nolonger hunt with its pack, it ussally goes off to die like StuRat said, i belive one of the documentries acctually stated that this is equivallent to committing suicide in the animal kingdom as the animal that leaves knows it has no chance or surviving on its own with out its pack. Perhaps a articl on Animal Suicide is in order? User:Maverick423 If It Looks Good Nuke It 15:28, 16 April 2007 (UTC)
male angler fish.
- Don't the rest of the pack actively drive the 'no longer useful' animal away, instead of it choosing to leave of its own accord? I've certainly read anecdotal accounts of this amongst gulls (if one bird is sick or injured, the rest will attack it until it either leaves or is killed) - the sickly flock member presumably being a liability to the rest. Apparently, albino gulls are subject to a lot of 'social pressure' too (this was actually cited in a scientific paper I read, though I cannot recall the details now)... --Kurt Shaped Box 22:25, 16 April 2007 (UTC)
- I'd like to see that cite. I don't doubt you, but it sounds counter-intuitive to me. Part of the benefit of living in a herd/ flock/ school is that you reduce your individual risk of predation because there are so many others around. If I was an antelope in the Serengeti, I'd be quite in favour of there being a few lame animals in the herd for when the cats start hunting; if there are easier targets sround, I might be left alone. Matt Deres 20:32, 17 April 2007 (UTC)
- In some cases female Black Widow spiders and Praying Mantis' devour the male after copulating. I guess you could say that the male commits suicide by doing that. SteveBaker 23:08, 16 April 2007 (UTC)
- Infected ants sometimes leave the colony and subsequently die.Polypipe Wrangler 06:22, 17 April 2007 (UTC)
Quantifying article
In article Center pivot irrigation there are no factual data given. Does someone know some data that quantify such an irrigation system? E.g. typical, average, even record length of array (yards or meters). Speed of rotation. Quantity of water pumped. Etc. etc. VanBurenen 14:27, 16 April 2007 (UTC)
A tree named Sag
According to our article about Purandhar as well as this page, "Some parts of Purandhar are covered with forest, which is composed mostly of Sag, Teak, Oak, and Mango trees." I've never heard of a type of tree called "Sag", however. Nor does Wikipedia have an article on such a type of tree. The closest I could find was Amaranthus dubius, a weed which is sometimes referred to as "Khada sag". Anyone have any clues as to what this "Sag" is referring to? Kaldari 16:36, 16 April 2007 (UTC)
- Looks like it may just be another name for Teak actually. Kaldari 16:43, 16 April 2007 (UTC)
- Maybe a misprint of Sal?—eric 17:31, 16 April 2007 (UTC)
Emphysema death breakdown
What is the breakdown of emphysema death causes? [Mαc Δαvιs] ❖ 16:54, 16 April 2007 (UTC)
- By far the leading cause of emphysema is cigarette smoking [5]. Air pollution and occupational exposure to airborne toxins round out the bulk of the remaining cases. About 2% of cases a attributable to A1AD, a genetic disorder. Have you Googled for numbers? TenOfAllTrades(talk) 02:51, 17 April 2007 (UTC)
I don't know jack about the beanstalk
Would the cable of the space elevator rise perfectly vertically or would it bend? If the latter, roughly how much? Clarityfiend 16:57, 16 April 2007 (UTC)
- Speaking generally and ideally, the cable remains taut and vertical. From a practical engineering standpoint, a completely rigid structure is a bad idea and so some flex would certainly be allowed for and expected. Also note the article subsection on cable lean. — Lomn 17:28, 16 April 2007 (UTC)
- If anchored at the equator, An ideal beanstalk will be vertical. If not anchored at the equator, it will not, but I'm not sure what will happen instead. -Arch dude 20:40, 16 April 2007 (UTC)
- Yet another reason it hasn't been built yet : ) Nimur 20:43, 16 April 2007 (UTC)
- I believe that one of the reasons why ship-born earth-side designs are looking good because it would be possible for the ship to move out of the way of major storm systems to avoid damage to the cable. It seems unlikely that the space-side end would be able to keep up - so I deduce that the cable is indeed allowed to lean somewhat. But since the cable would be considerably more than 35,000km long, the base would have to move an awful long way before there was any significant angular shift in the cable! You have to have a mental image of a cable that's three or four times the diameter of the earth! From that, perspective, a bend of a few kilometers - or even maybe a hundred kilometers is pretty negligable when distributed along the entire length. The tricky matter is whether very low frequency oscillations might be induced by wind shifts happening at close to the cables resonant frequency. Our article suggests that a one-degree lean might occur due to the coriolis effect on the 'climber' as it ascends the cable. SteveBaker 23:00, 16 April 2007 (UTC)
Viruses
I am writing a paper on viruse, and am a little confused!! Can viruses be destroyed by phagocytosis, or does this only apply to bacteria? Hope someone can help 81.101.49.156 19:40, 16 April 2007 (UTC) Chrissy
- Virtually any foreign matter can be consumed by phagocytes, viruses included. And like bacteria, viruses can be attacked by free roaming antibodies. Viruses can also be eliminated by the additional method of Natural killer cells destroying infected cells, to prevent new viruses from forming from it. Someguy1221 21:00, 16 April 2007 (UTC)
Thankyou for clearing that up for me 'someguy', much appreciated 81.101.49.156 22:16, 16 April 2007 (UTC)Chrissy
Hydroponics and Tequila
I've been reading up on hydroponics, and I recall an episode of the Colbert Report where a guest (I think it was Neil Young) proudly declared to have smoked pot that was hydroponically grown in tequila. The more I read about hydroponics, the more this strikes me as impossible. As I understand it the nutrient solution for hydroponics needs to be carefully controlled in terms of acidity and mineral concentration, and chucking spirits in there seems like a sure fire way to kill the roots. Is this at all possible? And if it is, does it have any effect on the crops? I somehow doubt that this will lead to tequila flavoured strawberries, even if it does work. risk 22:11, 16 April 2007 (UTC)
- Maybe he actually meant hydroponically grown in Tequila? Vespine 22:35, 16 April 2007 (UTC)
Or, I suppose, you could add one drop of the alcoholic drink of your choice to each gallon of water, which shouldn't kill the plants, but this certainly wouldn't affect the flavor of the plants which grow in it, either. StuRat 22:50, 16 April 2007 (UTC)
- Or maybe he was joking? It would not be unexpected to hear a comidic exageration the Cobert Report. -Czmtzc 11:50, 17 April 2007 (UTC)
- I don't think that was the case, but I may have missed it. In any case, it turns out that it was Toby Keith [6] and it was Willie Nelson's pot. Apparently Nelson got busted a week later, too. risk 12:51, 17 April 2007 (UTC)
- Or maybe he was joking? It would not be unexpected to hear a comidic exageration the Cobert Report. -Czmtzc 11:50, 17 April 2007 (UTC)
What's the age record for herring gulls?
Today, I encountered a gull that must be at least 25 years old now. I remember first seeing him as an adult when I was a boy - he has *very* distinctive plumage (looks like he has some sort of pigment disorder - large areas of his wing plumage are snow white, instead of grey, in a very distinctive pattern). I hadn't seen him for three years or so (he used to nest around here regularly), so I just assumed that he was dead and gone - but today, I saw him sat up there on his favourite perch (well, rooftop), watching the world go by. I'm certain that it's the same bird. Has anyone ever heard of an older member of this species? --Kurt Shaped Box 22:44, 16 April 2007 (UTC)
- Now how did I know who asked this question as soon as I saw the title ? Isn't it possible that the pigment disorder is inherited and it's offspring has also inherited it's favorite perch ? StuRat 22:53, 16 April 2007 (UTC)
- It's certainly possible Stu - it did appear that it was the same bird though. The particular pattern of white and grey on his wings was exactly as I remembered it. What are the chances of a pigment disorder manifesting itself identically, even if it is inherited? --Kurt Shaped Box 23:04, 16 April 2007 (UTC)
- There could be some selective memory at work, your memories of that bird from 25 years ago may have been adjusted to match the current bird. Do you have any photos of the earlier bird to ensure that you recall it correctly ? StuRat 00:46, 17 April 2007 (UTC)
- First, I will assume good faith, and that your memory is not faulty. According to this site Top ten bird lifespans of North America, the age records for the top ten range from 30 - 50 years. The birds in the list are all sea birds too. I personally do not think it is unreasonable that you may have a 26 year old bird. -Czmtzc 11:48, 17 April 2007 (UTC)
- Thanks for that guys. I'm willing to accept that it may be selective memory on my part - but it would be nice to think that the big guy was still alive and kicking. I have fond memories of throwing food into the air for him to catch from back when I was a kid. Because he looked slightly different to the rest, I singled him out and made sure that I always threw food in his direction. That's all it takes to make a gull start hanging around near your house (for those that might want a gull hanging around near their house). --Kurt Shaped Box 18:45, 17 April 2007 (UTC)
- Just in case you want them to "decorate" your car for you ? StuRat 07:03, 19 April 2007 (UTC)
Eris
From looking at Eris and the Definition of 'planet', how is Eris not a planet? Teak the Kiwi 23:21, 16 April 2007 (UTC)
- is in orbit around the Sun,
- has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and
- has "cleared the neighborhood" around its orbit.
- See 2006 definition of planet for some details. In my opinion, these are vague enough to allow astronomers some argument-room. Nimur 00:09, 17 April 2007 (UTC)
- I still don't understand, it looks close to a sphere, it is in orbit a round the sun, and from what I can figure out it has 'cleared it nieghborhood' (Its not like Ploto and Charon). If it is higher mathematics than Algebra I, just say so. Teak the Kiwi 03:07, 17 April 2007 (UTC)
- Eris is classified as a dwarf planet - the difference between that definition and that of a true planet is thr third one (above) "cleared the neighborhood". Since Eris has been classified as a dwarf, it must be that it has not cleared it's neighbourhood. SteveBaker 03:43, 17 April 2007 (UTC)
- That is indeed the case. It is clearly demonstrated at List of solar system objects by planetary discriminant. The discriminant is used as the measure of clearance. The lowest discriminant for the now-accepted planets is 24,000 (Neptune), whereas that for the minor planets is no higher than 0.33 (Ceres). Eris's discriminant is only 0.10. By this measure, Eris is nowhere near clearing its neighbourhood. JackofOz 03:59, 17 April 2007 (UTC)
- The definition is horrible. It was an attempt to avoid having very many new planets and at the same time include no completely arbitrary size restriction. The whole story is an example of the Paradox of the heap, where an essentially fuzzy definition (being large) is made precise. Do you remember the old sience fiction stories about mirror earth? The existence of such an object (there is none, I know, thank you) would make earth a dwarf planet under this definition. A raindrop floating around in free space is a dwarf planet by this definition. It is really unspeakably horrible. —The preceding unsigned comment was added by 84.187.17.11 (talk) 13:06, 17 April 2007 (UTC).
- I disagree. A raindrop floating in free space (part of it would vaporize and the rest would solidify pretty quickly, so it would rather be a hailstone) isn't round because of gravity but because of surface tension, therefore it wouldn't be a planet according to the definition. And with a mirror Earth Earth's orbit wouldn't be stable, and I would consider such a planetary system to be still in development - I think the chances are quite high that the two bodies collide within a few million years. Icek 17:31, 17 April 2007 (UTC)
- Yeah - there is no way a raindrop can qualify because it can't hold a spherical shape under it's own gravity, it would be completely unable to clear it's neighbourhood. Sure - they become spherical due to surface tension - but that doesn't make them planets. The "spherical under own gravity" requirement effectively puts a minimum size on what qualifies as a planet - so there is an implied lower size limit. But this is all irrelevent in the grand scheme of things - labels like 'planet' are arbitary - there are bound to be corner cases that cause difficulties. We get this kind of issue come up here every day or two on the science desk and the answer is - in truth - "This has nothing whatever to do with science - it's a branch of linguistics." SteveBaker 00:46, 18 April 2007 (UTC)
April 17
Whites of eyes
Is it true that humans are the only animals to have whites eyes (outside of the iris)? zafiroblue05 | Talk 00:04, 17 April 2007 (UTC)
- Sclera, the white part of the eye, does not say! I think other animals definitely have a sclera, but I don't know if it's white. I can't get a good image of many animal eyes to check... Nimur 00:27, 17 April 2007 (UTC)
- Nope - first pic I found. --Kurt Shaped Box 00:26, 17 April 2007 (UTC)
- While many other animals have sclera, the sclera in humans typically take up a much larger portion of the visible eye than in other animals. At least one biologist has suggested that having larger sclera was evolutionarily advantagious to humans as it made emotions easier to read (pretty speculative though). Someguy1221 00:33, 17 April 2007 (UTC)
- I don't know about reading emotion - but it does make it a lot easier to see what direction other people are looking. SteveBaker 01:35, 17 April 2007 (UTC)
- While many other animals have sclera, the sclera in humans typically take up a much larger portion of the visible eye than in other animals. At least one biologist has suggested that having larger sclera was evolutionarily advantagious to humans as it made emotions easier to read (pretty speculative though). Someguy1221 00:33, 17 April 2007 (UTC)
- Every dog I've seen has a white sclera. However the iris and pupil take up almost all the space in the visible eye socket, so you can't see it unless the animal diverts its eyes. [Mαc Δαvιs] ❖ 02:11, 17 April 2007 (UTC)
- I have seen dogs, etc. move their eyes just enough so that you can see a little bit like [Mαc Δαvιs] said. Teak the Kiwi 03:09, 17 April 2007 (UTC)
- You can see it in this image Image:Staffordshire Bull Terrier - Labrador Cross.JPG. SteveBaker 03:36, 17 April 2007 (UTC)
cute !
Prostate health
How many times per week/day should a man ejaculate to maintain optimum prostate health? —The preceding unsigned comment was added by 88.109.222.205 (talk) 00:09, 17 April 2007 (UTC).
- Too much can decrease your overall sperm count. But in all seriousness, you don't need to ejaculate weekly or daily to maintain your prostate. bibliomaniac15 00:36, 17 April 2007 (UTC)
- According to a study done by the Cancer Council Victoria in Melbourne, men who ejaculated 5 or more times per week were 30% less likely to develop prostate cancer[7], as it also states at prostate. Somebody said something mean to me several days ago when I said it is unhealthy to never ejaculate in a question about abstaining. Check that one too for some quote and references. [Mαc Δαvιs] ❖ 02:06, 17 April 2007 (UTC)
Inverted glass with water holds a card
If you fill a glass with water, place a card over it and turn it upside-down, you can remove your hand from the card and the card will remain in place. I understand that this has to do with the air pressure below, but
- Is the pressure of the water above the card really less that the pressure of the air below it?
- Is the density less? (obviously not)
- Why does the glass need to be filled with water? Wouldn't it be even easier with air? (obviously not)
Clearly I haven't precisely understood the experiment (you can view a video of it here). Can someone explain it to me a little better (or is there an article on it?). Thanks!
-- Josh, 02:03, 17 April 2007 (UTC)
- Uh! I think you may be misunderstanding what is happening. The glass is actually like a gigantic straw. You can drink from the straw because when you remove air from the top, a vacuum is created, and the fluid rushes up to fill that space, right into your mouth. In the glass, if the water (and card) tries to fall out, there is a vacuum of empty space at the top, and that sucks the water back up in again. [Mαc Δαvιs] ❖ 02:10, 17 April 2007 (UTC)
- Also need to consider the surface tension of the water. To make it work, may need to have the glass to be within certain limits on the ratio of diameter, water depth, and empty space above the water. DMacks 02:12, 17 April 2007 (UTC)
Can this sort of thing be generalized for all fluids? Or is this a water specialty?--Ķĩřβȳ♥♥♥ŤįɱéØ 02:20, 17 April 2007 (UTC)
- Atmoshperic pressure will support a column of 760mm of mercury as in a barometer, or a column of water about 30ft high. The card just allows the air pressure to act evenly over the body of the water with which it is in contact. Otherwise any light disturbance on the water surface would cause the water to pour out.
- Fill a tumbler under water and then raise it above the surface. The same effect is seen, but a bit of water sloshing in and out in this case is unimportant-- its not going to destabilise the whole thing.
- I presume the narrower the glass tumbler the easier this is to perform as the water cannot move about so much sideways.
- Of course in very narrow tubes, the capillary effect takes over.
In regard to vacuums sucking water up a straw, isn't it more accurate to say the pressure of the surrounding water pushes water up the straw because when the person sucks (ie. inhales the air in the straw), there's suddenly a space for the water to go into? JackofOz 03:38, 17 April 2007 (UTC)
- Correct. Suction is not an actual force, but more accurately, it's not that the water has someplace to go, but rather that there is no longer anything pushing it back (minor distinction). However, the water is actually pulled up slightly by the walls of the straw, although this effect is primarily observable in narrow tubes (as the unsigned comment above states. Someguy1221 03:48, 17 April 2007 (UTC)
The water serves two functions in the experiment:
- It makes a nominal seal so that the fluid inside the glass can't exchange with the fluid (gas) outside the glass, and
- It makes the experiment much more dramatic.
The glass could be filled with anything that allows the formation of a seal and has a denisty low enough that the atmospheric pressure pressing up on the card bottom can overcome the weight of the stuff inside the glass.
Atlant 12:58, 17 April 2007 (UTC)
- If you believe the effect depends only on the sealing you are completely wrong. The pressure of the water is the same as the pressure of the air when you fill it in the glass. If you turn the glass around, the original pressure plus the weight of the water is pushing from above and the same atmospheric pressure is pushing from below and the card will move downward. However: The capillary effect glues the edges of the card to the glass, and the card will bend instead of moving downward. Now the crucial effect comes into play: Water is essentially incompressible. The water will lose its entire internal pressure while extending only by a tiny fraction of its volume. The air pressure continues to push from below and keeps the card from falling. The experiment cannot work with air in the glass, even if you seal the edges with water, because the air will simply have the same pressure as the air outside (It does work with light cards, because of capillary force alone, but you can put small weights on the card in both cases to see a difference).
- Did I say that it depends only on sealing? Someone asked why water; I answered that. One of the reasons "why sater" is that water forms an adequate seal (for several reasons) to keep the water from escaping the glass in small runnels acted-on by gravity. If you think that doesn't matter, try doing the experiment with Helium II superfluid instead of water and let me know what happens.
- You said anything that allows the formation of a seal and that is not to heavy. I don't want to be offensive, but you wrote that just two paragraphs higher. As for Helium, my guess is that the card will fall down. However, my kitchen sink seems to be out of helium today. —The preceding unsigned comment was added by 84.187.32.191 (talk) 20:31, 17 April 2007 (UTC).
- And I stand by that statement ("allows the formation of a seal and is not too heavy") and haven't seen anyone disclaim it. I think I'm missing your point. Rather than debate what I said, why don't state your point (again?).
- Here's how I think about it. (And it's a fun experiment, which you should all try, but don't make the same mistake I did just now, namely holding the inverted glass+card too high above the sink, assuming it'll work the first time, because when the seal fails and the water comes splooshing out all at once, it splashes out of the sink all over your shoes. But I digress.)
- If you fill a long, thin tube or pipe with water, and seal it at the top, you will discover that the water trickles out very slowly, if at all. You can describe this in terms of suction or in terms of pressure, but it's also just a question of mass transfer. If the water is going to trickle out of the bottom, it has to be replaced by air. (And, indeed, if the long, thin tube is transparent, and the water is managing to trickle out, you will see bubbles slowly rising, moving opposite the water flow, collecting at the top as the water level lowers.)
- There's no magic involved here; we don't have to posit a special force which somehow defies gravity and keeps the water in the tube (or glass). If the tube or glass were filled with clay, or cement, or silly putty, or jell-o, or blackstrap molasses, or tapioca pudding, or ice, or some other solid or very viscous liquid material, we wouldn't be at all surprised if it didn't come out. Is it defying gravity? What's holding it up? Why, we're holding it up: we're holding the tube or glass, and the stuff inside is stuck to the tube or glass, so it doesn't fall down. Simple as that.
- Well, almost. Clearly there's a difference between solid materials like clay and cement and jell-o and ice, and viscous materials like silly putty and molasses, and liquids like water. Also clearly there's some kind of a difference between a thin tube or pipe, versus a wider-mouthed glass or jar. But where's the crossover point between a thin tube or a thick liquid where the effect obviously works, versus a thinner liquid or a wider vessel where we would expect the liquid to run out? Clearly there's a continuum.
- And there's one more factor to consider, which several others have noted: surface tension. Water tends to stick to itself, and to the walls of the vessel it's in. Among other things, this makes it even more difficult for (say) those bubbles to rise, moving opposite the water flow, in that long, thin, transparent tube I was hypothesizing. And the surface tension also plays a role at the bottom of the column of water, at the bottom end of the tube or glass you're expecting it to flow down out of. Obviously, you would think, all the dumb water has to do is pick a side, with the water flowing down out of one side, and the air rising up the other. But the water is too stupid to make this choice. Every spot on the bottom surface of the water wants to flow down and out just as much, and because all of it is trying, none of it can. It's a lot like commuters trying to exit a subway car at a crowded station, when there are so many people waiting on the platform impatient to board that the disembarking passengers can't get past them.
- So where does the card come in? We may believe that water can stay "upside down" in a thin tube that's closed at the top, as long as the tube is sufficiently long and thin (whatever that means). But clearly a glass is not long and thin enough, as we can easily prove by holding one upside down while it's full of water and noticing that the water does come rushing out.
- As I think of it, the card acts as a surface tension enhancer. Since the card is relatively inflexible (even when wet), it reinforces and enables that simultaneous impatience of every point along the bottom surface of the water to be falling out at once. The water can't bulge downward (beginning to flow) at one point, while simultaneously bulging upward (about to form a rising bubble) at another, because the dumb inflexible nonporous card is in the way.
- So what holds the card up? Well, it doesn't weigh very much, so the surface tension of the water does the trick. We don't normally think of water as an adhesive, but surface tension definitely makes it a weak one, as you can realize if you think about one of the ways you pick up a tiny object, too little to grasp between your fingers: just lick one finger and touch, and the object sticks to your finger.
- (Disclaimer: this has been a speculative, armchair explanation, with no actual scientific sources cited or even consulted. Apologies if anyone is offended by my lack of rigor.) —Steve Summit (talk) 02:47, 18 April 2007 (UTC)
emfs and internal resistance
If I had a circuit consisting of a battery with internal resistance that is hooked up to a variable resistor, and I know the terminal voltage of the battery and the current in the wire at a set resistance, would it be possible to determine the emf of the battery?
Thanks --K=.5mv^2 02:08, 17 April 2007 (UTC)
- The emf of the battery is just the open circuit voltage of the battery as measured with a voltmeter. You dont need any other stuff. However, if you are not allowed to open circuit the battery, see Internal resistance #Batteries. (replacing the apparently useful comment of a banned user Rockpocket 20:59, 17 April 2007 (UTC))
- Just to put a finer point on Rockpocket's answer, the reason you can (usually) accurately measure the EMF with just an ordinary voltmeter is that voltmeters normally have an input resistance that is many orders of magnitude larger than the internal resistance of the battery. If that isn't the case for the specific voltage source you're trying to measure, you'll either need to calculate (as you suggested in the question) or use a different instrument such as an electrometer.
Knife into head
I was wondering how easy or hard it is to stab somebody with a sharp knife, and penetrating their head. If you wanted to kill somebody and you had snuck up behind them, could you easily just smash the knife blade through their skull or not? I don't think the bone could be strong enough, because of the force of impact and concentration (knife point) is fairly unoptimal for the target. [Mαc Δαvιs] ❖ 03:09, 17 April 2007 (UTC)
- I would expect it would depend on where you hit the skull. If you hit at a weak spot, straight on, it would go in. If you hit at a strong point, at a slight angle, it would be deflected (but still cut the scalp up). Also, I expect a human cadaver would be needed for the experiment, as animal skulls of the same size tend to be much tougher. StuRat 04:25, 17 April 2007 (UTC)
- If they were standing up, I don't think the knife will go through, but you'll rip their scalp and push their head forward. --Ķĩřβȳ♥♥♥ŤįɱéØ 04:28, 17 April 2007 (UTC)
- Ah, so then it would be better if you hit the rest of their body? Where would be best anyway? [Mαc Δαvιs] ❖ 05:33, 17 April 2007 (UTC)
- If they were standing up, I don't think the knife will go through, but you'll rip their scalp and push their head forward. --Ķĩřβȳ♥♥♥ŤįɱéØ 04:28, 17 April 2007 (UTC)
Wikipedia does not provide Criminal Advice. We do not provide advice on how to kill a person most effectively, how to infiltrate your apartment while being surrounded by SWAT teams, or how to make meth in your kitchen. Ask a professional criminal instead.
- All jokes aside though, I guess somewhere near major arteries would be a good spot. --antilivedT | C | G 05:53, 17 April 2007 (UTC)
- Some martial arts defend against attacks of the knife held with the ice-pick grip and attacks to the head (or other parts) with said knife. BTW, take a look at where the Frontal bone and Parietal bone join... it is a spot of weakness. I suspect it is possible, if done at the right angle with the right instrument. If I tell you any more they would send someone to kill me ;-) Root4(one) 06:38, 17 April 2007 (UTC)
- I was told by a police officer that cutting the groin is probably the easiest way to kill someone with a single knife cut - obviously due to outbleeding. 213.48.15.234 07:33, 17 April 2007 (UTC)
- "If in doubt, aim for the groin." - effective on most men --antilivedT | C | G 09:37, 17 April 2007 (UTC)
- Oh yes, you can't underestimate the "OH MY GOD YOU JUST STABBED MY GROIN" effect. Why isn't there an article on that? 213.48.15.234 11:18, 17 April 2007 (UTC)
- Probably women. [Mαc Δαvιs] ❖ 18:36, 17 April 2007 (UTC)
- Professionals in this business have been called "cutthroats" for centuries, I am inclined to believe that this is no coincidence. —The preceding unsigned comment was added by 84.187.17.11 (talk) 12:49, 17 April 2007 (UTC).
- Oh yes, you can't underestimate the "OH MY GOD YOU JUST STABBED MY GROIN" effect. Why isn't there an article on that? 213.48.15.234 11:18, 17 April 2007 (UTC)
- "If in doubt, aim for the groin." - effective on most men --antilivedT | C | G 09:37, 17 April 2007 (UTC)
I suggest you Nuke them... using micro waves or something. might not be as fast but it looks alot cooler then stabbing... and how can we all forget the neck?? slashing the neck the only one that mentioned it was mr 84 ^^^. User:Maverick423 If It Looks Good Nuke It 13:25, 17 April 2007 (UTC)
- No, actually it wouldn't look that cool. They would feel burns underneath their clothing. Have you checked microwave gun? [Mαc Δαvιs] ❖ 18:36, 17 April 2007 (UTC)
- Guess not, because that's not an article yet. http://powerlabs.org/uwavexp.htm is the first thing that comes to mind. He's starting a page on the new one soon. [Mαc Δαvιs] ❖ 18:38, 17 April 2007 (UTC)
Yep its been talked about before maybe it deserves its own article =P if you recall last time i tried to burn stuff outside using a microwave which didnt work =( the chips and all that stuff burnt up before it did any damage. anyways a knife to the head is kinda primitive dont you think i mean with the tech we got now adays we can imaging some pretty fun (for the person using it) ideas on how to umm end a life. User:Maverick423 If It Looks Good Nuke It 21:34, 17 April 2007 (UTC)
I've hacked up a lot of chickens in my day, and even their puny bones take a good whack with a cleaver to get through. A human skull is probably enough trouble that you should probably just let go of your anger, and remember that the best revenge is living well. --TotoBaggins 13:34, 18 April 2007 (UTC)
Prevalence of freezing temperatures on Earth
Hi
I'm looking for some numbers for an introduction about how common temperatures below OC are on Earth. I'd love to be able to say "90% of the Earth's terrestrial environment experiences temperatures lower than 0C each year" or something like that. Does anyone have any insights and/or references about this? Thanks heaps for your help!
Aaadddaaammm 03:10, 17 April 2007 (UTC)
- That's an interesting question. I've never seen that information presented that way. But if you look up information about climate zones, such as the Köppen climate classification, you can find maps showing how much of the Earth's land area has each major type of climate, and you can find how the climate types are defined. (And a Google search on things like "climate" and "map" will take you to more pages.) That'll take you part way toward an answer, although getting from a map to an accurate percentage of areas won't be easy. (Ocean maps with climatic information are harder to find; you may have to settle for land only.) --Anonymous, April 17, 2007, 03:45 (UTC).
- Thanks for your reply - I did consider this kind of approach, but decided it was a bit too rough for my report. I really just want a throw-away statistic to get the paragraph started, and don't want to have to justify my calculations too much. Does anyone else have anything to offer on this question? Aaadddaaammm 01:17, 18 April 2007 (UTC)
CMOS and CCD image sensor comparison
If CCD is better than CMOS sensor, then why almost all professional SLR digital camera use CMOS as their sensor? roscoe_x 06:10, 17 April 2007 (UTC)
- From Charge-coupled device, "Since a very-high-resolution CCD chip is very expensive as of 2005, a 3CCD high-resolution still camera would be beyond the price range even of many professional photographers." --Wirbelwindヴィルヴェルヴィント (talk) 06:28, 17 April 2007 (UTC)
- Just backing up what Wirbel said, CCDs are not cheap! 213.48.15.234 07:34, 17 April 2007 (UTC)
- Then would it mean Canon Ixus is better than Canon EOS? If not, what make the EOS better? roscoe_x 08:21, 17 April 2007 (UTC)
- Because the sensor is much, much, much, much bigger and hence able to receive more light and hence higher SNR ratio and hence less noise and hence less detail diminishing noise reduction. Also, not almost all professional DSLR's are CMOS based, you forgot all the Nikon ones (among others). --antilivedT | C | G 09:35, 17 April 2007 (UTC)
spring !
im searching for a way to figure out the optimal proportion for a helical spring to propulse a person (lets say 150 lb)kind of like a trampoline and how many of those i would need
the thing is i want to figure out what the smalest amount i could use and still have a smooth unwinding and not take more than about 1 1/2" for the spring to be able to push back the weight
i also need to find out wich material would be good
clockwork fromage —The preceding unsigned comment was added by 216.113.96.143 (talk) 06:20, 17 April 2007 (UTC).
- The only thing that immediately springs (sorry NPI) to mind is that of a recoil spring in a (very) large field gun
/cannon. —The preceding unsigned comment was added by 88.111.93.83 (talk) 22:21, 17 April 2007 (UTC).
- There are equations that can help predict the behavior of a spring, including Hooke's Law. There are also calculators that can help you play what-if. As you can see, there are more variables than you have specified, so it's hard to give a definite answer without knowing more about the application you have in mind. How big around can the spring be? With what force are you trying to propel this person? Does the person's weight compress the spring, or does something else? Are you going for distance? How does balance factor in?
- Also, before you go propelling any human beings, please think about safety. Human beings who are propelled can fall on their faces, twist their ankles, and plenty of other things. --Dvortygirl 03:32, 18 April 2007 (UTC)
Genetics of ear-wiggling?
Some time after I wrote this article, others added these unreferenced claims:
- "The general consensus is that the ability to wiggle your ears is thanks to one gene, which has been turned off for some people."
- "Approximately twice as many men than women can wiggle their ears."
While I can attempt to describe the learning process from experience, I have no idea where I might verify or discredit these claims. Neither Auricularis nor Ear discusses these details of human ear motion. In the name of accuracy, thanks in advance for any direction you can offer. --Dvortygirl 07:19, 17 April 2007 (UTC)
- Many of the facial muscles not normally accessible as voluntary, can be learned. Ears are the same way, but not sure about the gene thing. [Mαc Δαvιs] ❖ 18:34, 17 April 2007 (UTC)
Effectiveness of 'low blow' against bear attack?
I reading one of those 'SAS survival guide' books a few years ago in which it was stated that as a last resort when being attacked by a bear, one should attempt to strike it repeatedly in the groin/testicular area. Just as a matter of interest - has anyone ever heard of anyone surviving a bear attack by kicking their assailant in the nads? This is the only reference I could find to someone attempting a groin attack on a bear - it didn't end well. --Kurt Shaped Box 11:39, 17 April 2007 (UTC)
- Different strokes for different bears. It's not something with a high success rate. --Zeizmic 12:04, 17 April 2007 (UTC)
- Have you seen the John West salmon commercial? - that seems to back it up quite well. Capuchin 12:39, 17 April 2007 (UTC)
- LOL! I've been trying to remember what that advert was selling for ages now. Great to see it again. Thanks. :) It was a memory of that ad that made me start the original 'man vs. bear' thread some time back (which spawned several 'x vs. y in a fight to the death' imitators). --Kurt Shaped Box 18:39, 17 April 2007 (UTC)
Lets not forget that that commercial had a human wearing a bear suit. User:Maverick423 If It Looks Good Nuke It 13:36, 17 April 2007 (UTC)
- But what if the bear likes it ? StuRat 17:05, 17 April 2007 (UTC)
- You'll probably die in an even more horrible, lingering way than if the bear had just crushed your skull and gotten it over with? --Kurt Shaped Box 18:40, 17 April 2007 (UTC)
- For some reason I don't think that precision strikes against large beasts would be effective, because when a 500 lb. behemoth of muscle and teeth is bearing down on you, you're only going to feel terror. Vranak
- Bigger beast, bigger testicles to kick? --Kurt Shaped Box 22:44, 17 April 2007 (UTC)
Does everything sink when it goes below a certain depth in the ocean?
A log floats. If I were to drag it deep enough under water, would the water pressure from above force the log down to the bottom of the ocean, or would the fact that the cellulose molecules would always be slightly less dense than the surrounding water molecules mean that the log would always rise to the surface? Is there some point of neutrality at a certain depth that would hold the log stationary until Brownian motion bumped it either up or down enough? — Jonathan Kovaciny (talk|contribs) 13:42, 17 April 2007 (UTC)
- The pressure at depth would have no directional vector (so would not force a log down/up or any direction) although it might cause the cells in the log to become more compressed and thus the log to be more dense. If the log became more dense than the surrounding water it would sink. Objects less dense than water will always float.David D. (Talk) 14:54, 17 April 2007 (UTC)
- The same would happen to the water though, as the pressure (and depth) increase, the density will as well, so the water may become more dense than the object. In this situation, there would be a depth where the object becomes neutrally buoyant, and it would remain there. anonymous6494 16:35, 17 April 2007 (UTC)
- Water will not compress as easily as wood (which has a lot of air space in the dead cell chambers) so the density of water will not increase as much as wood due to depth, if at all. Changes in water density are primarily due to temp and composition (salt and nutrients). There is a good figure here that confirms the density does not change significantly with depth. http://www.windows.ucar.edu/tour/link=/earth/Water/density.html&edu=high David D. (Talk) 20:09, 17 April 2007 (UTC)
No, not everything sinks when it gets to a certain depth. Some things always float (Styrofoam), some things always sink (lead cannonballs), some things will find a natural level within the water (some plants), and some will sink once they reach a certain depth (a submarine that implodes at that depth). StuRat 17:02, 17 April 2007 (UTC)
- In the case of the submarine, it doesn't necessarily sink. At surface, the submarine consists of the metal hull and the air inside. When it implodes, the air part quickly rises and the metal part quickly sinks. So, to be annoyingly technical, the submarine separates into the parts that float and the parts that sink. --Kainaw (talk) 18:50, 17 April 2007 (UTC)
- Or, if the submarine is at sufficient depth and the air content of the water is low enough, the air might dissolve into the water before reaching the surface. StuRat 19:21, 17 April 2007 (UTC)
- I dont think things usually find a "natural level". If something is even a little compressable, and especially if it has gas pockets, then neutral buoyancy is an unstable equilibriam. Nearly everything ends up either floating or sinking - unconscious divers for example.Polypipe Wrangler 21:56, 17 April 2007 (UTC)
I'll take this opportunity to recommend again the excellent book, "The Flying Circus of Physics", which addresses questions like this in spades. One item is on the topic of why a crate will sometimes float face-up vs. corner-up in the water. --TotoBaggins 00:01, 18 April 2007 (UTC)
- Most buoyant materials are relatively compressible. Water is relatively incompressible. So, yes, most things lose buoyancy as they sink, due to compression. Scuba divers are intimately familiar with this: as you descend, your wetsuit compresses and becomes less buoyant, and you have to continually add air to your buoyancy compensator to, er, compensate. (The compressed wetsuit also doesn't insulate as well, which sucks, because the water generally gets colder as you get deeper, too.)
- Deep-rated submersible vehicles use special, noncompressible buoyancy materials, such as syntactic foam.
- In answer to the original question, I suspect that most materials would sink past a certain depth, not because the extreme pressure "forces them down", but because the extreme pressure would eventually compress virtually any material below its buoyancy point. (There are exceptions, though they are few: deep-rated submarine pressure vessels and syntactic foam are two.) —Steve Summit (talk) 02:09, 18 April 2007 (UTC)
- The question is not whether the material is compressible, but whether it's more or less compressible than water. If you have a chunk of something that's slightly more dense than water at atmospheric pressure, but less compressible than water, then it is possible that it would be negative buoyant at the surface, but that when it sinks to a certain depth, the water would have become dense enough to make it neutrally buoyant, and there it would stop. I think there are lots of solids that are less compressible than water. The rare property is going to be that the substance is more dense than water at 1 atmosphere, but by such a slight margin that it's less dense than water at the bottom of the ocean. --Trovatore 02:20, 18 April 2007 (UTC)
- Good point. And this reminds me of Galileo's thermometer -- I wonder how applicable that is to this discussion? —Steve Summit (talk) 03:27, 18 April 2007 (UTC)
- The question is not whether the material is compressible, but whether it's more or less compressible than water. If you have a chunk of something that's slightly more dense than water at atmospheric pressure, but less compressible than water, then it is possible that it would be negative buoyant at the surface, but that when it sinks to a certain depth, the water would have become dense enough to make it neutrally buoyant, and there it would stop. I think there are lots of solids that are less compressible than water. The rare property is going to be that the substance is more dense than water at 1 atmosphere, but by such a slight margin that it's less dense than water at the bottom of the ocean. --Trovatore 02:20, 18 April 2007 (UTC)
- Collegues, pleaselook at the bathyscape article. A bathyscape consists of a tank of (relatively) incompressible oil tank, controllable ballast, and a heaviar-than water payload. If a substance is (relatively) incompressible, its tendancy to sink will not increase with depth. -Arch dude 03:29, 18 April 2007 (UTC)
- No one seems to have mentioned Archimedes principle yet. —The preceding unsigned comment was added by 88.109.207.222 (talk) 10:08, 18 April 2007 (UTC).
microbiology
Why is it important to differentiate glucose nonfermenters from Enterobacteriaceae? —The preceding unsigned comment was added by 209.213.220.109 (talk) 16:08, 17 April 2007 (UTC).
- My faith in science would be seriously shaken if I thought the future microbiologists of the world were getting their homework done by a bunch of Internet dweebs. --TotoBaggins 23:57, 17 April 2007 (UTC)
do fish like rain
I am curious to know if fish like rain, or how they react to rain. —The preceding unsigned comment was added by 69.236.22.85 (talk) 17:22, 17 April 2007 (UTC).
- Well, it is rather obvious that fish don't mind getting wet. However, the raid has different effects on them. It creates a darker atmosphere when it couds over - making it harder to see (though they can smell just fine). If the water is warm, a thin cool layer of water floats on top of the warm water for a bit - most fish don't care for that. They stay in the warmer water. If it is cold, a thin warm layer of water floats on top of the cold water for a bit, which draws fish closer to the surface. Heavy rains will cause water levels to rise. Fish tend to rise with a rise in water levels. Then, if it is a river, the current picks up. The fish have to swim against it or get swept downstream. That's a just a few things to think about. There are surely a lot more - such as the effects of acid rain on fish. --Kainaw (talk) 18:47, 17 April 2007 (UTC)
- I could also imagine the the action of raindrops impacting on water would increase the oxygen content a little bit.-Czmtzc 18:54, 17 April 2007 (UTC)
In brackish waters, as in the Florida Everglades, rain tends to decrease the salt content in the water (with high tides increasing it again). StuRat 19:17, 17 April 2007 (UTC)
- Rain would make lots of noise too, making it harder to hear other things.Polypipe Wrangler 21:59, 17 April 2007 (UTC)
Hypoxic tents
I searched a bit on these tents but they are pretty much too expensive for a poor student like myself, are there any good low budget methods to have similar results?Bastard Soap 17:47, 17 April 2007 (UTC)
- You could put together the component parts and it would be cheaper, but still expensive. You need an Oxygen tank, a Nitrogen tank, an air quality regulation system, and a semi air tight tent and constant refills for the gas tanks. Personally I would not want to use an amateur Hypoxic tent because I would not trust the oxygen concentration. What if your Oxygen tank ran out before your Nitrogen tank? You may never wake up. Czmtzc 18:02, 17 April 2007 (UTC)
- Also, in the presence of pure oxygen, many normally nonflammable things become flammable, like human flesh. So, only those with proper training should handle oxygen tanks. StuRat 19:13, 17 April 2007 (UTC)
Tapping on the fishtank...
I used to have a terrible habit of tapping on the glass of a fishtank whenever I happened to be passing one (I guess to make the fish look at me - which never worked anyway). I've been told off on more than one occasion for doing so and told to stop as "you'll kill the fish". Why does tapping on the glass harm the fish? --Kurt Shaped Box 18:55, 17 April 2007 (UTC)
- The thundering booms from your taps cause stress which reduce immunity levels which leads to disease and eventually death. --Kainaw (talk) 18:58, 17 April 2007 (UTC)
- Can you give a source for that? It sounds like an urban legend to me. I know that there have been stress related diseases with pigs in very bad living conditions, but fish? Just from hearing sudden loud sounds?
- They can sense that you're a reincarnated seagull? Clarityfiend 23:06, 17 April 2007 (UTC)
- Sometimes I do feel like I was a seagull in a past life. Did I ever mention that I can copy gull noises so well that the gulls will sometimes respond to them? ;) btw, the response you replied to wasn't mine... --Kurt Shaped Box 23:10, 17 April 2007 (UTC)
Asymptomatic carriers
Hello, me again. I'd like a bit more information on disease carriers; specifically, whether an offspring of someone with a recessive disorder will 'carry on' being a carrier of the disorder through three more generations. Lady BlahDeBlah 20:28, 17 April 2007 (UTC)
- If this is a disease that's inherited through simple mendellian genetics, the child of a carrier will have a one half chance of becoming a carrier himself. This can continue without end through any number of generations. Someguy1221 20:02, 17 April 2007 (UTC)
- So...a carrier who marries a normal person and has a child, that child will still/could be a carrier himself, and so on. Right? The disease I'm particularly thinking of, if it'll help, is what I got here last time I asked a question: Leber's congenital amaurosis. Lady BlahDeBlah 20:28, 17 April 2007 (UTC)
- Precisely. The child of a carrier and a noncarrier has a 50% chance of being a carrier, 50% chance of being a noncarrier. And any children who are carriers will have their own children follow the same probability. If a carrier were to marry another carrier, the children have a 50% chance of being carriers, 25% chance of being normal, and a 25% chance of inheritting the full blown disease. How long it's been since someone actually had the disease is irrelevent, and this is how you get carriers who have no idea that they even might be carriers. Leber's congenital amaurosis appears to be inherited in this fashion. Someguy1221 20:42, 17 April 2007 (UTC)
- Just to clarify, there are actually as many as six genetically distinct forms of Leber's congenital amaurosis (caused by mutation in different genes, including retinal guanylate cyclase and the RPE65 gene). This leads to the slightly odd situation where two parents who appear to suffer from the same genetic disease, can produce completely unaffected children. See PMID 12015276 for details. Rockpocket 21:14, 17 April 2007 (UTC)
- Colleagues, we are conflating Genetic disease with communicatable disease. A genetic disease is communicated via sperm or egg. The offspring will inherit the disease genetically from the father or mother via nuclear DNA, if the disease is "(nuclear) genetic", and from the mother, if the disease is mitochondlear. Under extremely rare conditions, the offspring might inherit a mitochondlear disease from the male parent. The offspring can become infected with a bacterial,viral, or fungal disease from the mother, completely independently from the act of conception: the mother and offspring are in intimate contact, permitting a pathogen to move from mother to offspring. In species where father and offspriong are in intimate contact, a pathogen can move from father to offspring. -Arch dude 02:34, 18 April 2007 (UTC)
- I don't believe the person posing the question was referring of a communicable disease, due both to their use to the term recessive disorder and their clarification they are interested in Leber's congenital amaurosis. Rockpocket 03:19, 18 April 2007 (UTC)
v = frequncy ?
I was taught that "v" stands for frequency, measured in hertz. How come it's not in the article "v" ? --24.76.228.161 22:19, 17 April 2007 (UTC)
- No its not 'v', its the greek letter 'ν' (nu) which admittedly looks a bit like a 'v' but isnt! For instance E=hν. The photoelectric equation. —The preceding unsigned comment was added by 88.111.93.83 (talk) 22:26, 17 April 2007 (UTC).
- The greek letter nu (ν) is often confused for vee (v), so many texts choose to represent frequency by the letter "f" to avoid mistaking it for velocity or voltage (as velocity and voltage are typically represented by v and V respectively). Someguy1221 22:29, 17 April 2007 (UTC)
- In Arial the characters are identical, unfortunately. The relevant link is Nu (letter). --24.147.86.187 23:38, 17 April 2007 (UTC)
- I was wondering why it looked different when I was editing it but then it looked identical here...Someguy1221 00:00, 18 April 2007 (UTC)
Oh, that explains it all...thanks. --24.76.228.161 00:53, 18 April 2007 (UTC)
- This is why I prefer to write E = ℏw ... er... make that E = ℏω. -- mattb 06:02, 18 April 2007 (UTC)
Dust Settles... Or Does It?
If you were to completely isolate your bedroom (airtight, no vibration, no light etc.), would the initial airborne dust particles eventually all settled down on something (bed, desk, chairs, floor), or would some remain airborne infinitely?--JLdesAlpins 23:25, 17 April 2007 (UTC)
- If they are heavier than air, they should settle, yes. --24.147.86.187 23:39, 17 April 2007 (UTC)
Perhaps Brownian motion would play a role? --TotoBaggins 23:58, 17 April 2007 (UTC)
- I suppose it's theoretically possible for brownian motion to keep particles airborne indefinitely - but it's really unlikely. We know that typical house-dust settles because clean, horizontal surfaces end up covered in dust - which must have settled out of the air. So 'normal' house dust would definitely settle out eventually. SteveBaker 23:59, 17 April 2007 (UTC)
- I guess it depends on your definition of "dust". Presumably a particle of a similar size to the air molecules would easily stay airborne forever, and dust bunnies fall quickly, and somewhere in between something might stay aloft for a good while. --TotoBaggins 00:06, 18 April 2007 (UTC)
- My sense is no, that microfine dust particles would stay aloft indefinitely, as minor variations in heat distribution in the structure of the house itself, from the sun and winds moving around outside, will keep the air moving, just a little. Vranak
- Interestingly, your body heat is easily enough to stir up dust and pollution, so if you have the right imaging techniques, you can 'see' your own plume of circulating air stirring up the dust, even if you are sitting still. Carcharoth 10:41, 18 April 2007 (UTC)
April 18
Hurricane names
Who gets the job of naming hurricanes? Do they have someone standing around with a book of baby names and write down random ones? bibliomaniac15 00:29, 18 April 2007 (UTC)
Change in velocities of orbits
"In the elliptical orbit, the center of mass of the orbiting-orbited system will sit at one focus of both orbits, with nothing present at the other focus. As a planet approaches periapsis, the planet will increase in velocity. As a planet approaches apoapsis, the planet will decrease in velocity."
The above is taken directly from the Wikipedia article on orbits. I was wondering why the planet increases in velocity as it approaches periapsis and why it decreases in velocity as it approaces apoapsis. Thanks a lot 208.96.96.207 00:41, 18 April 2007 (UTC)
- In a circular orbit, the force of gravity on a planet is always facing perpendicular to the direction of motion of the planet, and thus gravity cannot do work on the planet, and cannot change its
velocityspeed. In an elliptical orbit, however, on the approach to periapsis the force of gravity has a component in the direction of the planet's motion, and thus the planet speeds up. And on the way to apoasis, the force has a component opposite the planet's direction of motion, so it slows down. You could also interperet the change in velocity as a change in kinetic energy to exactly cancel the change in gravitational potential energy as the planet's distance from its star changes. You could also interperet it the correct way, with general relativity, but that would be nasty and unnecessary. Someguy1221 00:53, 18 April 2007 (UTC)
- In a circular orbit, the force of gravity on a planet is always facing perpendicular to the direction of motion of the planet, and thus gravity cannot do work on the planet, and cannot change its velocity.
- This is bullshit! Velocity is a vector and if gravity cannot change the velocity of the planet then the planet would move in a straight line and the planet would not be in a circular orbit. Obviously gravity can change the velocity of the planet. 202.168.50.40 01:11, 18 April 2007 (UTC)
- Calm down, corrected now. Someguy1221 01:13, 18 April 2007 (UTC)
- Goodness - that was a bit uncourteous. --bmk
- Calm down, corrected now. Someguy1221 01:13, 18 April 2007 (UTC)
- Although the distinction between "speed" (a scalar) and "velocity" (a vector) is always made in physics and is a useful one when talking about these concepts, it mostly isn't made in other fields. In particular, people involved with space travel tend to say "velocity" even when they mean speed: for example, they speak of escape velocity rather than "escape speed", even though escaping depends only on kinetic energy and therefore only on speed. (Okay, speed and not being on a collision course.) --Anonymous, April 18, 2007, 08:40 (UTC).
which paper towel are strongest?
68.96.105.152 02:09, 18 April 2007 (UTC)
I would guess Bounty as they seem to be obsessed with proving this, but it is probably the only good thing about them. I think this might count as advertising though. You should test it yourself to make sure.
Chinese to English Geology Dictionary
Dear Wikipedians:
Does anyone know where I might find a good online Chinese to English geology dictionary or translator?
Thanks,
70.53.61.246 04:10, 18 April 2007 (UTC)
"Perfect" insulation
Let's say I have a big hollow ball made of some magnetic material or other. The shell of this ball is quite thick, and is completely airtight. Inside the ball is just plain old room temperature air from my garage. Now lets say I enclose this ball inside another ball in such a way that the inner ball is suspended by magnets, and I've completely evacuated the air from the outer ball. (I now have a ball floating inside a vacuum.) Just for good measure, I cover the outer ball with a mirror surface. Next, having nothing better to do with my money, I ship my ball down to Antarctica and drop it (gently) on the ice. Will the temperature of the inside ball ever drop? — Jonathan Kovaciny (talk|contribs) 05:45, 18 April 2007 (UTC)
- Yes, because:
- 1) You can never completely remove all the air, so some conduction and convection will occur.
- 2) No mirror reflects all radiation, so some heat will be transferred by radiation, as well.
- This is just a variant of the perpetual motion machine. Perfect machines only exist in *expletive deleted* minds. Vranak
- Even if you assume that you have a perfect vacuum, heat can still be lost through radiation instead of the normal heat transfer. And when you have two metal spheres like that, I can't help but think there's some sort of surface charge effect that would occur that might change the temperature over a long period of time, but I'm not sure if that'd happen. --Wirbelwindヴィルヴェルヴィント (talk) 06:18, 18 April 2007 (UTC)
- I protest - this has nothing to do with perpetual motion whatsoever. This is a thermodynamic question, really. See blackbody radiation - if your outer shell is at a different temperature than the inner shell, the two will inevitably communicate energy via the radiation field between the shells, which will always exist. Entropy will increase, and your system will equilibrate! --bmk
- I see that I just repeated most of Wirbelwind's comments - sorry! --bmk
What planet is this?
I took this image in southern Uganda, looking west, north-west just after sunset (~8:00pm local time). I think that the cluster of stars just below the planet are the Seven Sisters (of Subaru fame). Also, Orion is just out of frame in the far upper left. I was a degree or two south of the equator. Thanks. --Cody.Pope 07:01, 18 April 2007 (UTC)
- By using this neat online sky simulator and entering approximate Ugandan coordinates (0 N 33 E) and your specified time (17:00 UTC) and direction (azimuth 280), I determined that your planet is Venus. --bmk
- BTW I doublechecked, and Orion is indeed up and to the left in the sky. --bmk
- Genius! I knew there were tones of programs and scripts out there for this, but I has having trouble finding one. Also, this too confirms that my star cluster is indeed Pleiades. --Cody.Pope 08:07, 18 April 2007 (UTC)
- BTW I doublechecked, and Orion is indeed up and to the left in the sky. --bmk
- Whenever you see a bright planet in the western sky shortly after sunset (or in the eastern sky around dawn), it's almost certainly Venus, which is the brightest object in the sky (after the moon) and never very far from the sun.--Shantavira 08:16, 18 April 2007 (UTC)
Genetic Tests
You sometimes hear of surveys about the genetic make-up of an area (like proving there's lots of Celtic genes in England for example), how would you get one of these tests for yourself to trace your ancestry? And what exactly can they test, is it only the direct male or female line?137.138.46.155 07:18, 18 April 2007 (UTC)
- National Geographic offers a home kit through their website. They track only your paternal (if you're a male) or maternal line (via Y-chromosome micro-satellites or mitochondrial DNA, respectively). Your lineage would then go into their database, though. You could find out from whereabouts your line came. I believe the kit cost 100USD. Do a search for "genealogy project" on their website. --Cody.Pope 07:27, 18 April 2007 (UTC)
Is there a lot of vegetation in the South of China?
I saw in a satellite map a representation of methane emissions, most of the "methane clouds" were caused by zones with heavy vegetation, such as in equatorial areas. Despite that, the biggest one was allocated in southern China, in a circle-like area. My question is: Is there such a huge amount of vegetation or are the Chinese just producing a "special" kind of pollution there? Thanks. --Taraborn 10:06, 18 April 2007 (UTC)
Please show us the map,'South China'is too genernal.I can't give a nice prediction without enough info.Anyway,as I know,South China is one of the relatively developed area of China.The presence of heavy vegetation is less likely to appear in such area.--lowerlowerhk 21:06, 18 April 2007 (UTC)
Vitamin B - Thiamin as a mosquito repellant
Hi
I'm writing to you from South Africa and currently in hospital with malaria. My question however deals with thiamin as a bug repellent.
I recently saw an advert for a bugpatch that claims to allow small amounts of thiamin (vitamin B1) into the skin which apparently keeps mosquito's at bay? Wikipedia explains what Thiamin is, its chemical constitution, etc, but no mention is made of its mosquito or bug repelling qualities. Could anyone perhaps tell me:
1. If Thiamin is an effective repellant; 2. If yes, why this is so?; 3. if one cannot get hold of a patch etc, would simply ingesting thiamin (e.g. vitamin B) syrup be effective?; 4. how much would a person have to ingest for it to be effective?
regards —The preceding unsigned comment was added by Andrerabe (talk • contribs) 12:03, 18 April 2007 (UTC).
- I remember that was big 20 years ago. Most of the 'alternatives' have been tested and found ineffective. --Zeizmic 12:18, 18 April 2007 (UTC)