Wikipedia:Reference desk/Archives/Science/2007 September 3

= September 3 =

Localized buckling
What exactly is localized buckling? deeptrivia (talk) 00:47, 3 September 2007 (UTC)


 * It's when a surface that should be flat looks something like this:

______ →________/       \_________←


 * This can be caused by many things, such as:


 * 1) Greater thermal expansion of the surface material than the underlying material (or greater thermal contraction of the underlying material), due to a different coefficient of thermal expansion for each material.


 * 2) Compressive forces in the directions shown.


 * Such buckling may be a warning sign of imminent failure of the object in question. StuRat 01:26, 3 September 2007 (UTC)


 * Mathematically, how is it different from the usual buckling? deeptrivia (talk) 02:25, 3 September 2007 (UTC)


 * Presumably it's a qualitative description indicating that the fault is localized to a specific area or material defect. Nimur 02:54, 3 September 2007 (UTC)
 * (Incidentally, is there a reason why our article on qualitative research exclusively mentions the social sciences?) Nimur 03:02, 3 September 2007 (UTC)


 * It's just in a small portion of the structure, versus over it's entire length. A local defect, such as partial delamination of the layers, may be why you get localized buckling instead of buckling over the entire length.  Localized buckling can actually be worse, as the forces act on a small portion of the structure, which may fracture, while, if they acted on the entire structure, it could withstand those forces. StuRat 02:57, 3 September 2007 (UTC)

I guess both localized and "global" buckling would correspond to a singularity in the stiffness operator of the system. Is there a way, then, to tell one from the other looking at the bifurcations of the system? deeptrivia (talk) 04:40, 3 September 2007 (UTC)

Numbness in foot

 * The following discussion is preserved as an archive. Please do not modify it. Subsequent comments should be made on the appropriate discussion page.  No further edits should be made to this page.

I dropped one of those metal folding chairs on my foot about 3 weeks ago, it hurt a lot and I was yelling, but as far as I could tell nothing broke and there was no swelling. Now its numb and I get this weird tingly feeling when I touch that area, does anyone know what happened? Did I damage some nerves or something? Is it going to be normal again? —Preceding unsigned comment added by 76.167.145.55 (talk) 02:00, 3 September 2007 (UTC)


 * You should really see a doctor. Wikipedia cannot provide medical advice.  Someguy1221 02:06, 3 September 2007 (UTC)


 * I agree, see a doctor, that sounds serious (perhaps a blood clot, which, if it were to break loose, could be life-threatening). StuRat 02:35, 3 September 2007 (UTC)


 * I think/hope you mean "I agree, see a doctor, I'm not going to speculate on medical issues" Aaadddaaammm 05:14, 3 September 2007 (UTC)


 * Actually, I've decided to indulge our OP just a little bit, and point him to our section on chronic numbness. But let me assure you that just about everything listed under "Causes" is reason to see a doctor as soon as possible.  Someguy1221 05:39, 3 September 2007 (UTC)


 * Stop giving medical advice! Chronic usually means the time course is >3 months, a "wierd tingly feeling" could feel quite different to pins and needles. In cases like these you say nothing but "please see a doctor", isn't that the policy? Aaadddaaammm 05:54, 3 September 2007 (UTC)


 * The policy is to not attempt to diagnose the OP, or recommend solutions to his medical issues, aside from informing him to see a doctor. Proving general information on medical conditions, or showing him where to find more information, is entirely within policy.  And if anything I said is medical advice, so is saying chronic implies > 3 months ;-)  Someguy1221 06:01, 3 September 2007 (UTC)


 * Aaadddaaammm, the only dangerous medical advice is "that sounds trivial, don't worry about it". Saying that it sounds serious (and giving examples of some serious possibilities) to get them to go to a doctor isn't dangerous, and not something we could be sued for, either. StuRat 14:15, 3 September 2007 (UTC)


 * I had something similar when I bumped my foot into something, which resulted in the sort of pain one feels when hitting a nerve. Indeed, that's what it was, so my doctor told me. Except that normally this pain subsides within a minute. This one took about half an hour. Turns out that nerve is permanently damaged and remains very painful to this day (about ten years later). The doctor told me there was a possibility that it could have been more dangerous (can't remember how), but that was luckily not the case with me. DirkvdM 09:32, 3 September 2007 (UTC)


 * The above discussion is preserved as an archive. Please do not modify it. Subsequent comments should be made on the appropriate discussion page, such as the current discussion page. No further edits should be made to this page.

Amalgam Illness
What is the incidence of mercury poisoning in the United States? —Preceding unsigned comment added by 151.204.143.134 (talk) 02:11, 3 September 2007 (UTC)
 * "Mercury poisoning is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH). This means that Mercury poisoning, or a subtype of Mercury poisoning, affects less than 200,000 people in the US population"   Rockpock  e  t  02:44, 3 September 2007 (UTC)


 * Given the title of this question you may also be referring to the Dental amalgam controversy. As best I know the general scientific consensus is that amalgam use has no significant side-effects in most cases. However this article gives a boatload of potentially useful references. --jjron 08:03, 3 September 2007 (UTC)


 * As the article states, it is a bit of a controversy to say the least. Some folks claim that everyone with amalgam filling ends up with the mercury in their system sooner or later. Other folks claim that it's all bogus. If the pessimists are right, however, then anyone with an amalgam filling would get mercury poisoning at some point in their lifetime, and therefor the incidence would be pretty close to 100% in certain age groups. Of course, amalgam isn't the only source of mercury (poisoning or otherwise). I expect that many older physics/chemistry teachers might have it, I had a few teachers who enjoyed playing with mercury in class, and if you do that often, poisoning is pretty much inevitable. There are also truths and rumours of mercury in the drinking water supply in some areas, which is potentially another source. That being said, amalgam is outdated and should not be used, regardless of mercury poisoning. There are superior alternatives out there, which last longer, look more natural, and are a lot less likely to poison you. I think that "glass carbomer" is the type of filling most recommended by amalgam-haters. I'm doing my best not to be too opinionated here, but I most humbly apologise if I fialed. Nimlhûg 10:44, 3 September 2007 (UTC)
 * You're casting an awfully wide net there. As far as I know, the ideal body burden of mercury is zero, and we all have more mercury than that. If that's "poisoning" then everyone is poisoned. But I think the question is more along the lines of how many people have identifiable symptoms that can reliably be associated with mercury. --Trovatore 17:26, 4 September 2007 (UTC)


 * An interesting case to check is comic writer Kurt Busiek, who, by a staggering coincidence, contracted mercury poisoning shortly after working on Amalgam Comics. Matt Deres 16:35, 5 September 2007 (UTC)

Entomology Question: Identifying Insects
Does anyone know what species these insects are? ,,. The pictures were taken in a backyard in a suburb of Southern California. —Preceding unsigned comment added by Schmoov (talk • contribs) 04:31, 3 September 2007 (UTC)
 * First two look like weevils from there I don't know.87.102.47.218 14:13, 3 September 2007 (UTC)


 * The first guy has the typical "true bug" markings of the order Hemiptera, but more specific than that I cannot be. --24.147.86.187 15:51, 3 September 2007 (UTC)


 * They are definitely "true bugs" (Order Hemiptera), not weevils, which are beetles. The leaf-like expansion on the hind legs distinguishes it as one of the Leaf-footed bugs in the family Coreidae. It is possibly Leptoglossus occidentalis a pest of conifer trees in California. The adult sucks the sap of pines and incense cedars. It neither bites nor stings. It defends itself by emitting an unpleasant smell. Try an image seach on google and see what you think. In your 3 photos, the reddish ones are presumably the immature nymphs (not larvae, Hemiptera do not have a complete metamorphosis).--Eriastrum 18:31, 4 September 2007 (UTC)


 * The nymphs are definitely assassin bugs. See this image. — Quin 02:10, 5 September 2007 (UTC)
 * Hmm, although I have just had correspondence with an entomologist who says that they're leaf-footed bugs (Leptoglossus occidentalis). The Wikipedia article on assassin bugs may have the wrong image. — Quin 04:58, 5 September 2007 (UTC)


 * Quin, I think you are right that the image of assassin bug nymphs in the wikipedia article is incorrect, and that it is of leaf-footed bug nymphs. If you notice, the nymphs have a very small enlargement on their hind legs that assassin nymphs do not. It might be a good idea to remove the nymph image from the assassin bug article. --Eriastrum 16:32, 5 September 2007 (UTC)

Pepper remains in the system for about 7 years...
Over the years I've heard a couple of times from different people that apparently pepper stays in the system for about 7 years- that it doesn't get digested or something.

There's nothing on snopes.com, theres nothing in Black pepper or its talk page, and nothing comes up on google - is there any truth to this claim? Can pepper be eaten liberally? Rfwoolf 08:52, 3 September 2007 (UTC)


 * I heard the same 7 year figure for chewing gum. I'm guessing it's an urban myth, but I have no evidence either way. —Pengo 13:41, 3 September 2007 (UTC)


 * Things which are not digested just pass through with your next bowel movement. (Hence sometimes you can "identify" things that didn't digest correctly. Bleh.) I would beware of any claims that various foodstuffs are not digested and somehow linger in your system (where would they linger?), they sound like old wives' tales. That which applies to chewing gum almost certainly applies equally to black pepper. --24.147.86.187 15:55, 3 September 2007 (UTC)


 * Pepper consist of hundred thousands of different types of chemical compounds - which one are you talking about (piperine?) Your body uses food compounds or their metabolites as building blocks, so, for example, calcium from pepper will end up in your bone and might stay there your whole life. But pepper is definitely not special in that respect. You might want to read digestion, metabolism, drug metabolism, and excretion. Cacycle 02:19, 4 September 2007 (UTC)

Eucalyptus as a source of gun powder
It is said to our Reasearch class that Eucalyptus leaves can be a source of gun powder. Some evidences are when a forest fire occurs, firefighters are hearing some little explosions that they found out that little explosions were bought by Eucalyptus trees. I found out that Eucalyptus leaves can be a source of gun powder, but are there bad effects when used?WikiPoTechizen 09:53, 3 September 2007 (UTC)


 * Those bangs are due to heat from the fire boiling up steam in a confined space that then breaks up its confines with a bang. Charcoal from the burnt wood could be used as part of the formula for gun powder, but don't expect to find oxidizing substances or sulfur in Eucalyptus. Graeme Bartlett 10:03, 3 September 2007 (UTC)

I mean what are the possible components of Eucalyptus that can easily burn up? Eucalyptus oil?--WikiPoTechizen 10:40, 3 September 2007 (UTC)


 * Yes, eucalyptus oil is flammable.
 * 1) However, being flammable is not sufficient to make something an explosive. An explosive must also contain an oxidising agent.
 * 2) Gunpowder is not a single compound. It is a mixture of three different substances.
 * 3) As Graeme Bartlett said, you won't find all of these three substances in Eucalyptus trees.
 * So, no, Eucalyptus trees are not a source of gunpowder. Gandalf61 13:16, 3 September 2007 (UTC)

Thank you for your information. —Preceding unsigned comment added by WikiPoTechizen (talk • contribs) 11:05, 6 September 2007 (UTC)

Contaminating Water Supplies
Just a question, with all of the Terrorist activity going on, They keep telling us that major supplies of water can not be contaminated, since it would become so dilute. But what about five pounds of ionized mercury, easily obtainable, or Dioxin, a byproduct of bleaching paper, also being the most carcinigant molecule know to exist?? I don't know if we are being told the truth both methods would seem to permantly polute a large watershead. P.S. If this is inapropriate delete it! Note that mercury is becoming extinct from the U.S. public example try to by a mercury thermometer, they have been around forever. Second mecury containing deviced have been replaced in hospitals, due to Pollution?..--Aaron hart 11:31, 3 September 2007 (UTC)


 * I'd say it's possible, but most terrorists want to kill people immediately, and make it obvious. Eventual deaths from cancer that may or may not be due to the contamination just wouldn't suit their preferences or serve to recruit more terrorists. StuRat 14:07, 3 September 2007 (UTC)


 * Look at the numbers. The Lake Joe Pool reservoir near where I live contains 618 Billion liters of water.  The average person drinks between 1 and 7 liters per day - but that's not all going to be from the same public water supply - let's be generous though and say that the reservoir contains enough water for 100 Billion people for one day.  That means that to cause people to die from drinking the stuff, you either need to dump 100 Billion times the lethal dose of whatever poison it is into the lake - or you have to put in enough of a cumulative poison so that it accumulates in the body.  However, in the height of summer, 30 million liters are taken from the lake each day - which serves about 15,000 people.  So of the 30M liters, only at most 100,000 liters of that is ever actually drunk - the rest is used by industry, for flushing toilets and filling baths or for lawn watering.  So the amount of a cumulative poison would have to be spectacular if it was going to make it into the population fast enough.  Also, the water coming from the lake is tested at least daily - so a cumulative poison would have to be administered very slowly in order to keep it in a low enough quantity to go unnoticed.  Hardly a great terror weapon.  As for Dioxin - a back-of-envelope calculation says that if you dumped a couple of 50 gallon drums of the stuff into such a lake, the resulting dosages for the surrounding population would be comparable to their lifetime dosages from eating farm-grown food in the USA.   I very much doubt that anyone would notice - let alone be terrorized by it.   That's not to say one shouldn't worry.  If that much was dumped in right next to where the water is pumped out ready to be purified and sent off to people's homes - then the concentrations would be much higher...but that's not a simple thing to do without getting noticed doing it.  A truck bomb in a crowded city center is a much more direct and vastly simpler terror weapon. SteveBaker 00:13, 5 September 2007 (UTC)


 * It could be argued that the 9/11 hijackers did both. Not only did we feel the immediate effects, but we're now beginning to see deaths and injuries from mesothelioma and other diseases caused by the asbestos-laden clouds of dust.  The injuries from this have the possibility of being worse than the original building collapses... and yet nobody really feels terrorized by it.  --Mdwyer 00:57, 5 September 2007 (UTC)

Picture
Who is the person in the picture behind Gell-Mann here ? Tintin 10:10, 3 September 2007 (UTC)
 * Ludwig van Beethoven.--Rallette 10:33, 3 September 2007 (UTC)
 * Thank you. Looked very familiar but couldn't place it. Tintin 10:37, 3 September 2007 (UTC)


 * i don't understand when you check the photos link, there are at least five people who state that it it Beethoven, so why ask?? —Preceding unsigned comment added by Aaron hart (talk • contribs) 11:05, 3 September 2007 (UTC)


 * In the flickr link ? I can't see it at the moment anyway because I am at work and it is blocked here ! Tintin 11:16, 3 September 2007 (UTC)
 * yes, my appologies--Aaron hart 11:33, 3 September 2007 (UTC)

Speed of Butterfly
When a butterfly fly in a bus. the bus run @60KMPH. Now what is speed of butterfly? —Preceding unsigned comment added by 203.197.157.138 (talk) 12:48, 3 September 2007 (UTC)


 * Not enough information. You don't say how fast the butterfly is flying relative to the bus, and in which direction. —Keenan Pepper 13:04, 3 September 2007 (UTC)


 * The velocity of the butterfly relative to the bus is the same as it's velocity relative to the ground would be if it was outside. It's velocity relative to the ground is the vector sum of the bus velocity and it's velocity inside the bus.  So, if the butterfly is moving 5 kph inside the bus, in the same direction as the bus, it's moving 65 kph relative to the ground.  If it's going the opposite direction of the bus, it's velocity is 55 kph relative to the ground. StuRat 14:00, 3 September 2007 (UTC)


 * Uh Sturat, what's the frame of reference, the Earth? I say the butterfly isn't moving at all.  I'd make him the frame of reference. :)  --Cody.Pope 16:17, 3 September 2007 (UTC)
 * He said "velocity relative to the ground." -Elmer Clark 01:14, 4 September 2007 (UTC)
 * StuRat said relative to the ground. Not anon. I'd make an Ultra-high-energy cosmic ray the frame of reference. Then it's one fast butterfly. — Daniel 03:10, 4 September 2007 (UTC)
 * (But it does explain how one flap of it's wing causes a hurricane on the other side of the planet! :-) SteveBaker 23:36, 4 September 2007 (UTC)
 * I see, next time I'll read more carefully. Haha. --Cody.Pope 13:09, 4 September 2007 (UTC)

How could cat kill a rabbit?
My cat is constantly bringing home dead baby rabbits. My question is above - I mean, a cat's mouth is far too small to break a rabbit's neck, and I don't see how it could choke one either. I suppose it could shake the rabbit's head until it had a brain haemorrhage, but probably not. EamonnPKeane 13:02, 3 September 2007 (UTC)


 * Rabbits are easily spooked, either by the cat or something like a lawnmower. Maybe the cat is just running off with unprotected baby rabbits? --  JSBillings  13:05, 3 September 2007 (UTC)


 * Yea, the mother rabbit probably flees. Rabbits reproduce so rapidly it doesn't make evolutionary sense for the parents to risk their lives to save the lives of their offspring.  The cat can probably bite the baby rabbits right in half. StuRat 13:54, 3 September 2007 (UTC)


 * Don't underestimate a cat's ability to break the neck of a small mammal. Cats are pretty good predators and know what they are doing. (Dogs too, I might add.) --24.147.86.187 15:45, 3 September 2007 (UTC)


 * Also don't underestimate the size of a cat's yawn; I can't imagine a wild rabbit neck that that wouldn't fit in there!  j e f f j o n  18:14, 4 September 2007 (UTC)


 * Cats can use a claw or their teeth to cut the throat of a small mammal. They can also possible strangle a small mammal by gripping the back of the neck fur tightly, or break the neck by biting (not necessary to get the whole head in the cat's mouth. A bite through the skull would also be a way of killing. Dogs will grab the head and shake the animal to break the neck;not sure if this is also a cat trick. Cats (and dogs) are also good at finding small dead animals and bringing them home as if they had killed them. Edison 18:58, 3 September 2007 (UTC)


 * Is it an urban myth that cats can kill by 'sucking the breath' out of their prey's lungs? Some sort of 'kiss of death'? I've seen cats kill small mammals before but I've never seen them do that. Just to raise the gull quotient of this thread, I have seen large gulls killing mice by breaking the neck with a bite, or shaking 'till it snaps. Not just a cat thing. --Kurt Shaped Box 19:06, 3 September 2007 (UTC)


 * They don't suck the breath out of lungs, that's preposterous. They have sharp little claws and teeth and can use them with expert precision. That's surely enough. --24.147.86.187 20:59, 3 September 2007 (UTC)


 * I believe that legend started by saying they suck the breath out of babies when they are asleep. The reason was that babies would have milk on their mouths and hungry cats would lick their lips.  Not knowing what they were doing, scared parents thought up the legend. StuRat 02:53, 4 September 2007 (UTC)


 * My nanna (she who raised me) told me that a stray cat got into the house and tried to 'smother' me when I was a baby. Apparently, the thing was over my face (though granted, it may have just been trying to sleep in my cot). She chased it off me, cornered it and killed it with a hot poker. True story. This may have been what could be considered excessive force. --Kurt Shaped Box 16:58, 4 September 2007 (UTC)


 * Yea, I think she would get arrested for cruelty to animals these days. The cat was probably just seeking warmth, they are masters of finding the warmest and coolest spots. StuRat 17:38, 4 September 2007 (UTC)


 * I don't think she's ever heard of the 'cats sucking the breath out of babies' thing - but she does certainly believe that 'cats hate babies'. She's mentioned to me several times about how cats should never be left alone with them. I guess that it's probably based on the same superstition. --Kurt Shaped Box 18:11, 4 September 2007 (UTC)


 * It's probably not a good idea to leave any animal with a baby, as they could harm the baby accidentally by sleeping on it (for warmth). I could possibly imagine a house pet being jealous of a baby, but plotting to murder the baby seems beyond their capabilities.  I can see dogs seeing a baby as prey, but not cats, since they don't hunt anything nearly that big. StuRat 18:35, 4 September 2007 (UTC)


 * They catch adult rabbits too.Polypipe Wrangler 00:44, 4 September 2007 (UTC)


 * Lions and other big cats can kill prey by suffocation: placing their mouths around a prey animal's nose. Not sure a house cat could do that. Delmlsfan 02:43, 4 September 2007 (UTC)


 * I don't think that's how they do it. When lions (or cats) suffocate prey, they do it by strangulation, not by covering the nose/mouth.  It'd be pretty hard to achieve a good seal on a struggling wildebeest and a lot more efficient to clamp down on the windpipe. Probably safer too, since even herbivores can deliver nasty bites.  As far as cats and rabbits go, I'd guess that an adult rabbit is about as large an animal a domesticated cat would likely try to bring down, but it's hardly an amazing feat; cats are superbly adapted to catching and killing small animals. Matt Deres 14:29, 6 September 2007 (UTC)


 * Not a rabbit but close; I had a guinea pig once who just dropped dead, presumably of fear?, upon being sniffed by a dog. No rough contact whatsoever.Gzuckier 15:24, 4 September 2007 (UTC)


 * I read about something similar in rhinos and hippos once. Scare them too much and they have some sort of adverse reaction to their own adrenaline (sorry, I can't be more specific - and I *do* read a lot of crap, so this may be crap!) and drop dead. Apparently, chasing them in a truck whilst firing a few round from an AK-47 over their heads will do it. If anyone knows what the hell I'm talking about, please elaborate... :) --Kurt Shaped Box 16:54, 4 September 2007 (UTC)

A bite through the skull would also be a way of killing. - this method of killing is unique to Jaguars, insofar as I am aware. See Jaguar Raul654 18:17, 4 September 2007 (UTC)

Boxes under a Spitfire's wing
I recently visited the Science Museum (London), the collection of which included large parts of several Supermarine Spitfires. I noticed a structure on the underside of both wings which wasn't explained by the displays.

The museum's version had two (apparently identical) structures, on on the underside of each wing. Each is a squarish box located inboard of the wheel well, toward the rear of the wing's undersurface. It's open to both the forward and rear direction, and the rear half of it articulated, forming a kind of flap. So clearly it's intended for air to pass through it. Due to the orientation of the museum's display it wasn't possible to look through the box to see what, if anything, might be inside that space. The boxes are visible on this photo of another spit.

Here is a photo of a Spitfire with the box clearly visible, but where the museum's aircraft had identical boxes on both sides (as in the first photo), the second picture shows only one, with a dissimilar narrower structure on the other wing. The Hawker Hurricane appears to have a similar device (centrally located under the fuselage) as seen in this model, and this diagram of a Focke-Wulf Fw 190 shows a vaguely similar port which appears to be for a turbocharger.

Supermarine Spitfire variants talks about some spits that had "two stage" superchargers, others that had "one stage" ones. Are these boxes for the supercharger? If so are the-two box spits those with the two-stage superchargers? Where was the supercharger itself located? Surely you'd want it as near to the aircraft's centreline as possible, to reduce angular momentum for rolling, and if indeed it was in the fuselage then why didn't the aircraft have a single central scoop like the Hurricane or the Fokker? -- Finlay McWalter | Talk 17:05, 3 September 2007 (UTC)
 * I'm no plane expert but aren't all those boxes air intakes for the engine?87.102.47.218 17:47, 3 September 2007 (UTC)
 * Correction the 1 or two boxes are air intakes for radiator cooling (that's for the spitfire) - it's likely the same for the others....87.102.47.218 18:00, 3 September 2007 (UTC) see here []


 * The supercharger is connected to the crankshaft - as you would expect - I'm 99% certain of this. Ignore- thinking of something else.
 * Why the thing is off centre I've no idea...87.102.47.218 18:02, 3 September 2007 (UTC)


 * There was normally two on each spitfire. One is the water radiator.  The other is the oil cooler.  It is possible that the water radiator and oil cooler were adjusted to be the same size on later models.  Originally, one was about three times wider than the other.  See this for a ref.  Under the image, it points out that one is the water radiator and the other is the oil cooler. --  k a i n a w &trade; 23:36, 3 September 2007 (UTC)
 * In the ref you gave - the picture [] only has one intake —Preceding unsigned comment added by 87.102.21.232 (talk • contribs)
 * According to this page, the Mk V used round oil coolers. --  k a i n a w &trade; 23:38, 3 September 2007 (UTC)

atoms
where was G .Johnson Stonely born? —Preceding unsigned comment added by 195.189.181.130 (talk) 17:16, 3 September 2007 (UTC)
 * That name provides no Ghits, could you be more specific about whom this individual is? Rockpock  e  t  18:33, 3 September 2007 (UTC)


 * Since that name gets absolutely zero google hits as spelled, I'm not sure that's an answer anyone is going to have. Maybe you got the name wrong? Maybe you can give us more information? --24.147.86.187 18:34, 3 September 2007 (UTC)


 * Eric Henry Stonely Burhop?.Aaadddaaammm 22:49, 3 September 2007 (UTC)
 * ... was born on 31 January, 1911 in Hobart.  Rockpock  e  t  23:30, 3 September 2007 (UTC)


 * With a surname like Stonely, it's more likely he's from either Nimbin or Griffith. :) --  JackofOz 13:44, 4 September 2007 (UTC)

Appearance of computer screens on television
Why is it that when computers are seen on-screen on the TV (say on the news), the computer screens flicker rapidly? They don't seem to appear like that in films or TV entertainment programmes. Is this just a phenomenon with British TV or does it happen with other countries' television networks? Rusty2005 18:49, 3 September 2007 (UTC)


 * Aliasing because the sample frequency of the television is close to the sample frequency of the monitor.  UK television samples at 50 Hz.  Depending on the montor, the difference between the TV sample rate and the monitor refresh rate is seen as flicker.  --DHeyward 19:11, 3 September 2007 (UTC)


 * The computer monitors (CRT monitors, more specifically) draw the image line by line, starting at the top of the screen and going down, over and over again (between 60 and 120 times per second or so). When a point on the screen gets passed by this sweep, it lights up brightly in its appropriate colour. Then it starts to fade, and by the time it gets drawn again, it has faded considerably. So it does actually flicker quickly, but the human eye smears this out so when you look directly at the monitor, you don't notice. The electronic eye of a TV camera does not smear it out, however. When it captures an image (about 25 times per second), it sees the computer monitor as it happens to be at the moment – some areas shine brightly (because they have been recently drawn) and some are darker. (Try this with an ordinary still camera to see what I mean.) Sometimes, it might so happen that the computer monitor has completed precisely one full sweep (or two, or three…) by the time the TV camera takes its next image. If so, you (watching the TV programme) would see a steady image on the computer monitor (some areas bright, some dark). If the computer monitor completed one full sweep (or two, or three…) and then some, you would see the bright-and-dark pattern roll across the screen. It might also happen that the screen completes one (or two, or three…) and a half sweep before the camera takes its next image. Then the bright-and-dark pattern will have progressed half-way across the screen between the images, causing a big change in what parts are bright and dark. This you see as flicker. It repeats 12,5 times per second (every other image) in this example, which is too slow for the eyes to smear it out, so you actually see it. Did it help? Well, I tried. Actually, older TV cameras (many of which are still around, I'm sure) take the images in a sweeping fashion as well, but the principle remains. —Bromskloss 19:47, 3 September 2007 (UTC)


 * Add to this that it is possible to match the rate that the pictures are taken with the rate that the screen is being drawn, resulting in a steady image as described at the beginning of Bromskloss's description. This is quite tricky and time consuming though, so if you're just filming a quick spot for the news, it's not really worth sorting out. You can also avoid the problem by putting the image in later. Skittle 22:12, 3 September 2007 (UTC)


 * And old cell phone video camera I had had a special setting for recording computer/tv screens that eliminated the flicker. Any idea how it worked?  There were no tricky or time consuming steps to it...Someguy1221 00:06, 4 September 2007 (UTC)


 * Perhaps just setting the exposure length of each frame to a multiple of the typical refresh interval of such screens? TV screens tend to flicker at 50Hz (PAL/SECAM) or 60Hz (NTSC), so an exposure length of 0.1 seconds ought to work for most TV systems, as well as most common computer screen refresh rates.  It's also close to the kind of frame rates I'd expect of a cell phone camera.  This is just a random guess, though.  —Ilmari Karonen (talk) 02:36, 4 September 2007 (UTC)


 * Isn't that what multimeters do to cancel out the ubiquitous disturbance from the power grid? —Bromskloss 07:08, 4 September 2007 (UTC)


 * As for movies showing TV or computer screens, they typically digitally add in the program later, flicker-free, rather than use an image recorded by a TV camera. Since computer screens in movies only have about 10 lines of text on them, they'd have to go out of their way to make a computer do that, anyway. StuRat 02:42, 4 September 2007 (UTC)


 * Thanks everyone, I'd always wondered that! Rusty2005 13:25, 5 September 2007 (UTC)


 * When you see TV screens on a TV show, the eliminate the flicker by syncing the TV's refresh to the camera. It is my understanding that TVs used in TV newsrooms and such have an additional input to receive the sync signal.  Everything in the room is basically running off the same clock. &mdash;Bradley 03:55, 6 September 2007 (UTC)


 * And, of course, more-modern display technologies like liquid crystal displays and plasma display panels don't flicker like CRTs did, so there's no longer any need for fancy synchronization or 24 FPS video or any of that tricky stuff.


 * Atlant 12:55, 6 September 2007 (UTC)

Moon Visible Daytime
It is now 1200 P.M. in Spokane, Washington the sun is high above the horizon, why is it only half the moon is visible?67.185.27.163 19:03, 3 September 2007 (UTC)


 * You only see the part of the Moon that is illuminated by the Sun at the moment. —Bromskloss 19:14, 3 September 2007 (UTC)


 * We have an entire article on Lunar phases. This will explain the process very thoroughly.  Nimur 19:34, 3 September 2007 (UTC)


 * The other half of the moon has taken Labor Day off. --24.147.86.187 20:58, 3 September 2007 (UTC)

The axle and wheel
I'm in an argument about the efficiency of rotational motion versus a piston stroke. The opposing argument is that since the piston stroke is well deployed in nature and nature has had longer to make changes to improve efficiency that it is more efficient than the axle and wheel. I disagree but before I sign off I want to find examples in nature of mechanisms used for locomotion, or what have you, that use rotational motion rather than back and forth oscillation to provide locomotion, pumping action or whatever.  Clem  21:13, 3 September 2007 (UTC)


 * The flagella and F1Fo-ATP synthase. Aaadddaaammm 22:39, 3 September 2007 (UTC)


 * To expand on Adam's answer, we've got a good article with pictures and animations of ATP synthase in motion. TenOfAllTrades(talk) 01:01, 4 September 2007 (UTC)


 * It seems esier just to point out that there's no practicle way to have unlimited rotation in most natural curcumstances. If a single blood vessel attaches from the axle to the wheel, it will get twisted around the axle as the wheel spins, and either stop the locomotion or break. — Daniel 01:26, 4 September 2007 (UTC)


 * Don't forget tumbleweeds. StuRat 02:17, 4 September 2007 (UTC)


 * It didn't work very well for hedgehogs, who now prefer to run. And the hoop snake never got off the ground.--Shantavira|feed me 08:22, 4 September 2007 (UTC)
 * Yeah, rotation is biologically very tough to provide. I remember it was quite a breakthrough when the mechanics behind the rotation of a bacterial flagellum was figured out. Gzuckier 15:27, 4 September 2007 (UTC)


 * Also note that that opposing argument isn't really an argument at all. While a human engineer seeks out the optimal solution to a given problem, evolution just throws everything at the wall and sees what sticks.  There's no reason to think that it would have arrived at a particular design just because it's better in some respect; it just needs to be good enough to make it to the next round of play.  --Sean 16:34, 4 September 2007 (UTC)


 * Right, there has to be an evolutionary path to it. Since a lumpy wheel is absolutely useless, you never get to a smooth, circular wheel. StuRat 17:32, 4 September 2007 (UTC)


 * Careful. How sure are you that a lumpy wheel is "absolutely useless"?
 * The arguments that "half a wing is absolutely useless" or "half an eye is absolutely useless" are frequently advanced as arguments against evolution. Yet as Richard Dawkins and others have persuasively argued, half a wing might be very useful if it allowed you to run faster or flutter a bit to escape a predator, and half an eye might be... well, "In the kingdom of the blind, the one-eyed man is king".  And a half-good wheel might be just as differentially advantageous, until further selection managed to round it off more perfectly.
 * (But it's true, a wheel and axle does seem to be something biological systems have trouble with. Heck, even the T-1000 couldn't manage it.) —Steve Summit (talk) 01:57, 5 September 2007 (UTC)


 * A "lumpy wheel" is less useful than other, non-wheel, means of motion. A partial eye (say one that only senses "light" or "no light") can still be quite useful, and a partial wing would allow for short-range gliding, which is useful by itself. StuRat 06:31, 5 September 2007 (UTC)
 * You have to be really careful about this - evolution doesn't always (or perhaps ever) work in an obvious straight line from problem to solution. Whilst a 'lumpy wheel' might be useless for locomotion on land, it's possible that it might first evolve as a mechanism for propulsion through water - or to use as a means to 'flail' open shells or something.  Once the thing evolves to that state, it can proceed to become a mechanism for propulsion.  Think about how feathers first evolved as 'fluffy scales' to keep dinosaurs warm - then switched to being useful for flying - then for sexual displays (think peacocks) - then back to keeping birds warm (think penguins).  Mechanisms don't have to evolve for their final purpose. SteveBaker 19:01, 5 September 2007 (UTC)
 * StuRat, you yourself pointed out a successful lumpy wheel: the tumbleweed. --Sean 19:29, 5 September 2007 (UTC)
 * Well, it's a wheel of sorts - but we're really talking about a "wheel and axle" per the OP - and we're stuck with flagellums as the only example in nature. SteveBaker 23:26, 5 September 2007 (UTC)
 * If this were article space and I were feeling snarky, I'd stick a "citation needed" tag after "A lumpy wheel is less useful than other, non-wheel, means of motion". I'm sure we could come up with plenty of non-wheel means of locomotion that a lumpy wheel is better than.  (The inchworm, for starters, and quite possibly snakes, too.) --Steve Summit (talk) 23:55, 5 September 2007 (UTC)
 * Not to mention snails. --Anon, 22:34 UTC, September 6, 2007.


 * The way I'm reading some of the above answers is that examples of "wheels" already exist in nature, they're just very small. Friday (talk) 17:39, 4 September 2007 (UTC)
 * Yep - I think the few cases of bacterial flagellums are the only true examples of wheel/axle setups in nature. Those organisms are primitive enough that the flagellum itself doesn't need nutrients, a nerve connection or anything tricky like that. But in higher organisms, that stuff ends up being very hard to engineer - and evolution simply never got into that niche.  SteveBaker 20:39, 4 September 2007 (UTC)