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November 7

my girlfriends disorder?

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This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

Lanfear's Bane | t 09:16, 7 November 2007 (UTC)

Diversity Antenna?

I remember way back in college that there was some discussion about diversity antennas (Using two antennae to increase signal strength or reduce noise, I think). It's was used in disccussion about wireless mics in TV (why many ENG news cameras have two floppy antennae sticking out of their back) I can't seem to find any entry on diversity in regards to radio waves on Wikipedia. What's the science behind it and what's it called? --24.249.108.133 00:08, 7 November 2007 (UTC)

See Antenna diversity. --Milkbreath 00:14, 7 November 2007 (UTC)

The quality or strength of the field can fluctuate wildly from point to point, so if you get the signal from a bad position you can compensate by using the good signal. Also two different polarizations can be used. The signal varies due to diffraction and destructive interference Graeme Bartlett 00:44, 7 November 2007 (UTC)

Sun and moon at midday

I live in the state of Virginia (US). A few days ago I went out to lunch from work on a pristine, blue-skied, bright autumn day...and there it was. The moon, 3/4's full and as clear as if I were looking at its craters on the clearest of nights; only the background wasn't black, it was a blinding bright blue. I looked back and forth at the sun and the moon and my watch (which read 12:45 pm) for quite a while and couldn't believe it. It was beautiful. Sadly, in just an hour the phenomena ceased.

I have lived here all my life (a respectable 27 years) and have never seen the sun and the moon together so prominently sharing the sky of midday. Is there any way to predict when this rare optic event will happen? —Preceding unsigned comment added by Sappysap (talk • contribs) 01:14, 7 November 2007 (UTC)

It sounds as though you saw a sun dog. Possibly due to ice crystals Graeme Bartlett 01:56, 7 November 2007 (UTC)

Actually, the sun and moon share the sky approximately half the time. When the moon is full, it's on the opposite side of the Earth from the sun. When it's at either quarter, it's at a 90° angle relative to the sun and thus above the horizon for about 6 hours of night and 6 hours of daylight. As the moon approaches its new phase, it's in the sky almost entirely during the day.

So as you can see, this isn't rare at all -- it's just a matter of stopping to look up. Additionally, the moon isn't the only celestial object visible in full daylight. Early this year, Comet McNaught was visible in full daylight, and Venus is often visible with binoculars, and with the naked eye at sufficient altitude. — Lomn 02:13, 7 November 2007 (UTC)

(after edit conflict) It's not a rare optical event at all, even though it may seem to be because the Moon is much less noticeable against a bright blue sky than against a black background. The Moon is up exactly as often during the day as it is at night.

Anyways, during your lunch break, the Moon will be up every day from full moon to new moon. The atmospheric seeing wil change from day to day and when you'll see the Moon cripsly will depend on chance. --Bowlhover 02:25, 7 November 2007 (UTC)

The only thing you won't see is a full moon in the daytime sky along with the sun. Just about anything else is possible. (But I agree, a daytime moon can be a lovely sight.) —Steve Summit (talk) 03:16, 7 November 2007 (UTC)

That's not true - at dawn or at sunset, the moon can be on the opposite horizon from the sun and in that case it will be a full moon. Someone reading this is just thinking to argue that it can't be quite 100% full if the sun and moon are both actually visible - and when they do that I'm going to find a large baseball bat and beat them into a quivering heap whilst yelling "AT-MOS-PHER-IC DIFF-RAC-TION YOU ID-I-OT!!". I'm hard - but fair. SteveBaker 03:37, 7 November 2007 (UTC)

Yep. What struck me about the original poster's report is that when the moon is close to full, it spends most of its time in the night sky and not so much in the day sky. (For a crescent moon, of course, it's the opposite.) So to see the moon 3/4-full close to noon actually is fairly unusual. Arbitrarily guessing Richmond for the poster's location, I plugged some different dates into this page and figured out that the date in question must have been Tuesday, October 30. The moon was 73% full and in Richmond it set at 12:50 pm. And of course the moon being close to the horizon triggers the moon illusion and makes the sighting even more impressive. --Anonymous, 07:33 UTC, November 7, 2007.

I saw he same thing on the same day at same time from near Dulles airport. I have lived here since 19770. What was unusual about that day was that the air was extraordinarily free of any pollution. What I noticed first was that the sky far from the sun as the darkest I have ever seen at midday, and there was a very obvious gradient (darker to lighter blue) toward the sun. I attribute the lack of pollution to the fact that we had just had a rain after the longest drought in about 20 years. We usually have a lot of urban pollution and a lot of terpene "pollution" from the mountains to the west. The moon was about half-way from the sun to the darkest part of the sky. -Arch dude 17:42, 7 November 2007 (UTC)

Bindeez to GHB??

Apparently these toys can be converted to 4-Hydroxybutanoic acid when swallowed... The toys apparently can be arranged into some pattern and will set when you put water on them..

http://www.theage.com.au/news/national/victoria-bans-toxic-toy/2007/11/07/1194329268448.html

Anyone know what the beads are made of? 1,4-Butanediol according to http://www.news.com.au/perthnow/story/0,21598,22712449-2761,00.html

So how about a conversion mechanism? Assumingly it has acid is involved in the conversion. Been a while since I've done organic chem but this looks like a very simple conversion... How did this ever get on the market??— Shniken1 03:07, 7 November 2007 (UTC)

Obviously first one of the hydroxy groups gets protonated... draws electon density from the carbon... promotes nucleophillic attack..?Shniken1 03:10, 7 November 2007 (UTC)

Oh well, not to worry - you can still buy them online here: http://www.redsave.com/products/Bindeez-Super-Studio-Design-Centre,,22 (eeeekkkkk!!!!). —Preceding unsigned comment added by SteveBaker (talk • contribs) 03:47, 7 November 2007 (UTC)

[1]. It's a fairly common chemical reaction, although I'm not sure how this would happen in the body, or if it would necessarily happen in this manner. (and damn you, Steve Baker, your edit conflict somehow crashed my web browser.) Someguy1221 03:52, 7 November 2007 (UTC)

In the body it looks like it's converted using alcohol dehydrogenase and aldehyde dehydrogenase (from the 1,4-butanediol article. GHB = 4-hydroxybutanoic acid). Maybe someone with more biochem experience can give more info --Bennybp 03:59, 7 November 2007 (UTC)

The account I read suggested that the toxic versions were made of different stuff to the normal versions, which were a non-toxic glue. So the ones you buy online might be safe. Or not. Skittle 04:01, 7 November 2007 (UTC)

The Counterpartness (Not a Real Word, But You Know What I Mean) of Human Races and Animal Breeds

I know that the topic of whether or not the idea of "human races" is biological or scientific is controversial in general, but what about when comparing them to breeds of animals? The idea of being a "breed of animal" is considered biological and scientific, is it not? And aren't human races and breeds of animals counterparts? And, if so, then why do the words "breed" and "race" exist separately and are not one word, as humans are scientifically animals (I know this has to do with history, but, if my assumptions are right, then why hasn't a word been been developed)? Also, if human races and animal breeds are counterparts, then why is there controversy over whether or not human races are biological and scientific? I know that included a lot of questions, but any help on any part would be great! Thanks! —Preceding unsigned comment added by Pitman6787 (talk • contribs) 05:43, 7 November 2007 (UTC)

A brief answer, but this undoubtedly go further. As you suggest the origin of the words is undoubtedly historical rather biological as the concepts are similar - it's just another case of a different word being used largely through the antiquated ideas of humans not being animals, and the consequences of that mode of thought. Now if you read the breed article you'll see the second sentence says "For a type to be recognised as a breed, there should be a viable true-breeding population." This has always been a big issues with human races - there is not a viable true-breeding population in any so-called race - basically given any contact there is immediate crossbreeding, and there is huge variation within populations. One of the other significant problems is that definitions of human races are distortions - claimed characteristics of given races rarely, if ever, hold true across that 'race'. Another problem is simply the misuse of race given almost any chance - why look for tenuous and largely non-existent differences and claim them as scientific when they will be mainly used for political and discriminatory purposes, and when the truth is that our similarities are far greater than our differences? --jjron 08:14, 7 November 2007 (UTC)

"Now if you read the breed article you'll see the second sentence says....", why bother go that far. The first damn line says a breed is a DOMESTICATED subspecies. So by definition, a human population can't be a breed simply because humans are never domesticated. So we are talking about subspecies. And it is thought, biologically, that the differences between the so called, races, are not significant enough to be classified as different subspecies. Different races have different colored skin, some differences in noses, hair texture, and eyes, but that's it. That's not significant enough to classify as a different subspecies. Perhaps if these groups were isolated and remained isolated for hundreds of thousands of years, then we would observe more pronounced differences between the different human populations. 64.236.121.129 21:10, 7 November 2007 (UTC)

There are several differences between breeds and races, some of which are more a matter of degree rather than clear-cut distinctions:

For one thing, with dog breeds for instance, in general the genetic variation between individuals within a breed is much smaller than the genetic variation between breeds. This is reversed with race: the genetic variation between races is much smaller than the genetic variation of individuals within one race.

Looked at another way, dog breeds in general consist of very clear-cut, genetically isolated populations. In contrast, with humans the prevalence of various genotypes and phenotypes often changes gradually over a geographic area, with less in the way of clear-cut boundaries. Because of the above and other complications, it’s very difficult to try to define and test for race genetically. See Race and genetics.

Within one geographical area, it may feel like there are reasonably clear-cut distinctions between races, if that geographical area contains large groups of people that had been relatively genetically isolated within recent history. For example, it works at least to some degree to group at least a lot of people in the U.S. based on whether most of their ancestors came from Europe, from western Africa, or from southeast Asia. But that moderately workable grouping to a large extent disappears if you consider all the people in the world as a whole, in which there are more gradual genetic variations over geographical areas.

Another difference between breeds and races is that there is a cultural aspect to race. Whether two populations of humans are grouped as one race or two depends a lot on how culturally similar or dissimilar the two populations are perceived as being. This is yet another reason why it is very difficult to try to define race in any rigorous way. See Race (classification of human beings). MrRedact 08:39, 7 November 2007 (UTC)

Material Properties in outer space

Hi, In hearting about the ISS unfurling their solar array and having it tear and all that - it got me wondering... Aren't these materials near Absolute_zero? Doesn't metal and plastic freeze solid at absolute zero? I guess not. —Preceding unsigned comment added by InverseSubstance (talk • contribs) 06:46, 7 November 2007 (UTC)

Why do you think that the temperature at the ISS is near absolute zero? The atmosphere at this height is quite hot. Not that this would matter - the temperature of the ISS is far more dependent on radiative heat transfer. Icek 07:06, 7 November 2007 (UTC)

The problem with this stuff is that somewhere, somehow, some scientist let slip the idea that space is cold. The truth is that space isn't any temperature. Temperature is (essentially) a measure of the average speed that atoms are moving around within some substance. No atoms - no temperature. So let's get rid of that idea. The temperature of spacecraft comes about in the same way things do down here at sea level - you add up the energy coming in (mostly sunlight - but also reflected earth-light and heat generated on-board the craft) - and you subtract the energy going out (by reflection of sunlight, and emission of infra-red light). If there is more energy coming in than going out, the temperature goes up and if more is going out than coming in, the temperature goes down. If the temperature increases, then more and more infra-red light is emitted and eventually you reach a temperature at which sufficient IR light is leaving that the temperature strikes a perfect balance. Similarly if the temperature falls, so does the IR emission and again, the temperature eventually stabilises. This is the same mechanism we have down here on earth - except that we also gain and lose energy by conduction into and out of the surrounding atmosphere and the ground. Also we get more incoming heat from scattered light from the sky.

OK - so those are the mechanisms. What happens with the solar panels? Well, as sunlight comes in, they heat up, the temperature slowly rises and they heat up - and when the spacecraft orbits around to the dark side of the planet, there is no more sun - so the temperature slowly decreases. The space station orbits (from memory) about once every 75 minutes. So the temperature of the craft goes up for about 37 minutes then cools off for 37 minutes over and over again. The large metal components take a long time to change temperature by much so they are going to tend to settle down to some more reasonable average temperature. So imagine a large chunk of metal down here on earth - if you take a large chunk of steel (a car perhaps) at some nice toasty temperature (because you've been driving it) and park it out in the snow in mid winter, would it cool down to freezing in 30 minutes? I don't think so. It certainly won't cool down to absolute zero over just 30 minutes! In earth, the car is cooled both because it's radiating IR light - but ALSO because it's heating up the air around it - that hot air rises and is replaced by cold air - so that's quite an efficient way for the car to lose heat. But up in space, there is no air - so it can only lose heat by radiation. That means that our solar panel will take MUCH longer than the car to drop to freezing point - and VASTLY longer to cool of to anywhere close to absolute zero - and it's only in the dark for 37 minutes in each orbit.

Another way to think about this is to watch the movie Apollo 13. Those guys had to live for nearly a week in an unheated spacecraft. The lunar lander got cold - but no so cold that they couldn't survive in their flight suits. Those spacecraft had to be spun so that one side of the craft wasn't perpetually in sunlight and the other perpetually dark. The ISS orbits - so that's not necessary for them.

SteveBaker 18:58, 7 November 2007 (UTC)

Regarding the original question, the relevant metals and plastics are of course already frozen (solid) at room temperature.

Regarding 70.116.10.189's answer, a little nitpicking: There are atoms - and even molecules - up there, but the density is too low to have a significant impact on the ISS's temperature. Even at more than 780 km height, where ERS-2 orbits, the atmospheric density is at least several hundred particles per cubic millimeter.[2]

And the space station's orbital period is 91 minutes.

Icek 14:25, 7 November 2007 (UTC)

Two Questions about Gravity.

Okay. Why isn't there a "nuetral" gravitational force? Okay. Let me explain. I think I was told by a teacher that, if there were no gravity on a planet, then it would be virtually impossible to reach it, as no force would be pulling you in. But, at the same time, that would seem as if there were a "negative" force keeping you away from the planet. But, why would there HAVE to be a force pulling you INTO a planet to be able to reach it, when there is NO "negative" gravitational force keeping you AWAY from it? That doesn't make any sense to me. Why isn't there "neutrality" in gravity?

Also, wouldn't we not have been able prove that gravity existed until we proved there were "gravities" that have different levels of force than Earth's? My thinking is that, until we proved there were "gravities" with different levels of force than Earth's, the only "gravity" that we knew existed was on Earth, with equal gravitational force on everything. So, basically, as far as we knew, gravity had only only level of force, but, knowing that, how could we prove it existed? I wish you could see into my mind, as my thinking is much better than that --- I just can't put it into words. It's like, since we knew there were different levels of force, we knew there had to be a force at all. Okay. Lets say humans were the only were the species that existed (work with me here), and we still classified the human being as a "species" --- like saying gravity existed when there was only, as far as we knew, one level of gravitational force. So, if there were only one type of species, then how could we prove that the concept of a "species" existed? Or, let's say EVERYTHING in the universe moved at the exact same speed (work with me here). We couldn't prove that a concept of "speed" existed, as, only one speed existed, right? We use the word "speed" because there are different speeds. If everything moved at the same speed, then we couldn't say "He's running fast" or "He's running slowly" or "He's moving at [number]/[unit] [length of time]." We could only say "He's moving", right? Or, if there were only color in the universe, we couldn't call it a color, right? We couldn't prove that the concept of color existed, unless we found a different color, right? It's like, if EVERYTHING in the universe had a quality about it that was the EXACT SAME, then how could you call it or prove that it was a characteristic at all? --- there would only be one type. I hope you know you what I mean. And I'm not saying that, even if there were only one level of gravitional force in the universe, that gravity wouldn't exist. I'm just saying that, before we found out that there are different levels of gravity, we really didn't have any proof that gravity existed --- knowing that there are different levels of gravity REALLY proves that there some kind of force exists, right?

Any help would be great! Thanks! —Preceding unsigned comment added by Pitman6787 (talk • contribs) 06:58, 7 November 2007 (UTC)

Re the first question, that's nonsense. Firstly you wouldn't have a planet without gravity, but let's just say you did. Saying that you couldn't get there because the gravity wouldn't pull you in is like saying you can't navigate to an arbitrary place in empty space because there's nothing pulling you in - but you can navigate through empty space to any given point. Your instincts are right, that there's nothing preventing you getting there. I'll leave the second question to others. --jjron 07:54, 7 November 2007 (UTC)

I would say for the second one, the problem is the inability to test variables that are beyond our capability to create or measure. The ancients knew well that gravity pulled anything that wasn't too light towards the center of the earth, but until Newton, no one figured a way to test gravity outside of the earth. And then finally, Henry Cavendish found a way to both eliminate the earth's gravity from affecting measurement, and measure the gravity between metal spheres. Similarly, until the 20th century, testing the extremes of small distances and great velocities was beyond anyone's capabilities. As such, while we were certainly capable of imagining classical mechanics as applying just the same to such conditions, this was entirely not the case. When people found ways to test them, they confirmed laws that changed the way physicists thought about the world. Someguy1221 08:39, 7 November 2007 (UTC)

Excellent questions ! Why does the gravitational attraction between two bodies depend on their masses but not what they are made from ? Why isn't there such a thing as anti-gravity paint ? Why doesn't anything have negative mass (as far as we know) ? Why is gravitational mass equivalent to inertial mass ? It was thinking deeply about these sorts of questions that led Einstein to the general theory of relativity in which gravitational forces are due to the curvature of spacetime. Gandalf61 10:57, 7 November 2007 (UTC)

Yes, you do some real thinking. What you say about our not seeing a thing that has no variation is quite true. That's part of the reason it took so bloody long to figure it out. Hats off to old Isaac, eh? You might be the one to see the remaining things of that kind. Keep us posted. --Milkbreath 12:17, 7 November 2007 (UTC)

We (well, people like Kepler and Newton) observed the orbits of other moons and planets and deduced from that that there must be a force attracting planets and comets towards the sun and a force attracting moons towards the planets. It's not much of a stretch to deduce that the smaller, lighter things are producing less force than the bigger, heavier things. You can go on to calculate how much force the earth is exerting on the moon - and with a sufficient leap of imagination - that the apple that just fell onto your head was being pulled by the same exact force (well, the apple story is probably apocryphal - but you get the idea). From the outset, we knew of many different sources of this mysterious attractive force. It was hard to quantify it because you can't easily figure out the mass of something that you can only see through a telescope as a blurry dot - but it must have been very clear that the gravity due to (say) Jupiter was vastly greater than that of Mars because you can SEE that Jupiter is huge, even in a primitive telescope. So they knew there was some kind of size/strength relationship. They could also figure out the decreasing pull of gravity as a function of distance. It took more careful experiments with big iron balls and very accurate measurements to get the details and the math exactly right - but the fact that there were differences and that the earth wasn't the only thing that had gravity must have been known for a very long time. SteveBaker 18:56, 7 November 2007 (UTC)

I wouldn't say so. While the idea may have occurred to people, the Aristotelian/Platonic system of celestial spheres was widely accepted (in the West) until Galileo began his astronomical observations in the early 17th century. Someguy1221 19:02, 7 November 2007 (UTC)

Omega-3 fatty acids in water-inhabiting animals

Why are omega-3 fatty acids so prevalent in water-inhabiting animals? They are prevalent in unrelated species, like whales, fishes and crustaceans. I guess they are produced somewhere near the bottom of the food chain. Is there some evolutionary advantage for omega-3 producing water-inhabiting animals? Icek 07:13, 7 November 2007 (UTC)

Quite a few prevelant microalgae produce omega-3 fatty acids. And yes these are on the bottom of the oceanic foodchain, so anything consuming them will also be rich in omega-3 fatty acids. As a matter of fact many fish can barely synthesise their own omega-3 fatty acids, and thus are almost fully dependent on microalgae. As to the evelutionary advantage of producing these specific fatty acids as opposed to producing others I do not know. PvT 12:54, 7 November 2007 (UTC)

Correct design?

Little Boy design is shown as having a round bullet with a cylindrical hole being fired at a cylinder shaped plug that fits in the hole. This arrangement seems counter intuitive to firing the cylinder plug into the cylindrical hole so as to avoid the problem of a rounded projectile twisting out of alignment versus the plug only being able to rotate in the gun barrel. Why was the arrangement shown used instead of the other way around? Clem 07:51, 7 November 2007 (UTC)

Little Boy#Counter-intuitive design. I think your link answered your own question. Someguy1221 08:43, 7 November 2007 (UTC)

The first picture does not seem to show the projectile as a hollow cylinder but rather as a hollow ball. Even with the alignment question answered it is still not totally clear to me why the hollow cylinder has to move instead of the plug. ...until you include the Tungsten-Carbide tamper as part of the movable projectile or stationary target. Clem 09:12, 7 November 2007 (UTC)

I think the first picture is just meant to be schematic in a cartoony way. --24.147.86.187 15:30, 7 November 2007 (UTC)

The page basically says that the larger area is actually more than one critical mass (which is certainly true) but kept from being critical by being in a tube shape (it has a hole in the middle so the uranium isn't too close to itself). If you put that into the large neutron-reflecting tamper you'd run the risk of too many neutrons spontaneously floating around and creating a criticality accident. So you keep that part far away from the neutron reflectors, and only when you bring it together is it subjected to their reflection. I don't know if that is true or not but it sounds plausible to me. You'd have additional problems created by such an arrangement but it might let you use more uranium to compensate. --24.147.86.187 15:33, 7 November 2007 (UTC)

One of the scarier experiments they did when designing that bomb was described in one of Richard Feynman's books - they actually dropped the cylindrical tube part over the core part experimentally to try to measure the amount of neutrons that would be produced - but they arranged that the tube would not stop when it was in the right position for an explosion - but merely keep on going. The theory being that if you could do this fast enough, you could avoid the chain reaction getting big enough to make a nuclear explosion. However, since they weren't 100% sure what the outcome of the experiment would be until they did it, it was always possible for something to go horribly, horribly wrong! Needless to say, this was a pretty dangerous experiment because if anything got stuck or moved just a bit too slowly...KABLOOIE! The building where they did those tests was way, WAY out in the desert! SteveBaker 18:28, 7 November 2007 (UTC)

Actually, they managed to kill at least a couple of people working on the Manhattan Project through careless manipulation of near-critical masses of radioactive material. See Criticality accident#Incidents, Harry K. Daghlian, Jr., Louis Slotin. TenOfAllTrades(talk) 19:01, 7 November 2007 (UTC)

derivation of phrase sex maniac

would like to know what the specific derivation is as not common in english language to use maniac with other terms eg dont describe someone as a chocolate maniac or a drug maniac.86.4.107.45 10:05, 7 November 2007 (UTC)

See Hypersexuality. The concept of hypersexuality replaces the older concepts of nymphomania (or furor uterinus) and satyriasis. Lanfear's Bane | t 10:37, 7 November 2007 (UTC)

Chicken-eating spiders

To my astonishment, I found this statement in the Raising Chickens Wikibooks:

"In south America there is a type of spider that will prey on chickens"

What kind of spider is that? It must be huge... --Taraborn 11:10, 7 November 2007 (UTC)

The Goliath birdeater is native to South America and seems to be a contender for the largest spider in the world [3]. However, despite its name it seems it does not normally eat birds - our article says it got its name because one specimen was once seen to eat a hummingbird. So very doubtful that it, or any spider, could prey on chickens. Gandalf61 12:16, 7 November 2007 (UTC)

...said he a moment before the Gargantua wizardeater, a species as yet unacknowledged by Western science, sank its glistening poisoned fangs into the nape of his neck. --Milkbreath 12:47, 7 November 2007 (UTC)

Don't forget good old Shelob. Lanfear's Bane | t 13:15, 7 November 2007 (UTC)

It can prey on a chicken and still be a pretty modest spider. If it has a venomous bite - then it could certainly kill a chicken and yet be pretty small - that a small spider might eat a small amount of a dead animal might not be surprising. I don't think we can dismiss this just because we can't imagine a two foot spider pouncing on the chicken and ripping it limb from limb with inch long fangs! SteveBaker 18:20, 7 November 2007 (UTC)

Civil engineering: Factor of safety?

in Civil engineering- what is a Factor of Safety ? and why do we use it ? —Preceding unsigned comment added by 82.69.206.166 (talk) 12:26, 7 November 2007 (UTC)

Welcome to Wikipedia. You can easily look up this topic yourself. Please see factor of safety. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. .--Shantavira|^{feed me} 13:44, 7 November 2007 (UTC)

Put simply: If you are building (say) a bridge and the heaviest truck you expect to cross it weighs 20 tons, you shouldn't build a bridge that can only support 20 tons because you know damned well that some idiot is going to drive a 21 ton truck across it - and you probably suspect that the steel you built it with is only 95% of the strength they said it would have at the steel mill, so it'll only really support 19 tons anyway. Then you know that the bridge will corrode some over it's lifetime and maybe the crew who build it make a little mistake and don't put the rivets quite close enough together - and maybe you didn't realise that in 100 years time, the bridge will have been painted 10 times and so it's now got half a ton of paint to support as well as that truck. So right at the outset, you look at the 20 ton limit and you say to yourself "I'd better build a bridge that can support 30 tons - and that way I'll be OK no matter what". The extra 10 tons you added is the "Safety factor" for the bridge. Of course you shouldn't over-do this because it's likely that a bridge that can cope with (say) 40 tons will cost twice as much as one that'll only support 20 (or was that 19?). That's all there is to it - nothing complicated. SteveBaker 18:01, 7 November 2007 (UTC)

Too obvious to be realizable?

What is the process by which plant cells transform carbon to oxygen, and can it be synthesized? If so, is that technique applicable to reducing carbon in our atmosphere? If not, how unrealistic an idea is this? Beekone 14:04, 7 November 2007 (UTC)

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and into oxygen and glucose. Your idea of carbon sequestering is a good one...see also our Carbon dioxide sink article. DMacks 14:23, 7 November 2007 (UTC)

See photosynthesis for details on the process. Note that this reaction requires energy (sunlight) to occur, so we would need enormous amounts of energy for significant results (think of how many trees there are in the world, and multiply that by at least 100 to get the total weight of algae, which produce about 80% of our oxygen). From the article, "Through photosynthesis, sunlight energy is transferred to molecular reaction centers for conversion into chemical energy with nearly 100-percent efficiency. The transfer of the solar energy takes place almost instantaneously, so little energy is wasted as heat." This means that not only would we need huge solar panels or lots of nuclear plants to do this cleanly, but we still would be nowhere near as efficient as plants. That's not to say it isn't possible: certainly the reaction produces food on the order of Soylent Green in artificial sugar-rich goodness, which might be very economical in the future. But as far as significantly impacting the CO2, I sincerely doubt it would have much effect. We're better off by first and foremost switching all our power plants to renewable and nuclear sources, which would be necessary for the reaction to have net effect anyway. SamuelRiv 14:30, 7 November 2007 (UTC)

Since when was photosynthesis efficient? Biological processes are notorious for being inefficient. I heard a retired biology professor say that photosythesis was inefficient. 64.236.121.129 16:22, 7 November 2007 (UTC)

Depends what you mean by "efficiency". To quote the article: "This chemical energy production is more than 90% efficient with only 5-8% of the energy transferred thermally." but "Not all wavelengths of light can support photosynthesis.". DMacks 19:21, 7 November 2007 (UTC)

It just struck me as such an obvious solution that surely someone had thought of the implications. I thought I'd leave it up to you guys to drop some knowledge on me. Thanks for pointing me in the right direction, very interesting stuff! Beekone 14:52, 7 November 2007 (UTC)

I do vaguely recall some experimental setup with large polythene bags full of some liquid that you'd lay out in the sun and bubble air through to capture the CO2 and produce some kind of useful product - it's not in widespread use though which suggests that there was some problem with it. But the answer is simple enough - cover a greater percentage of the earth's surface with plants (restoring the sahara to greenery would help for example) and stop cutting down the rainforests and starting forest fires! You can even harvest the plants (so long as you plant new ones immediately afterwards) and either use them to make ethanol/biodiesel to run your car sustainably or (if you actually want to sequester CO2), toss the dead plants into an anaerobic landfill someplace (so they don't produce methane as they rot).

Sadly, the very effect we're trying to prevent (global warming) is the exact same effect that's causing deserts to increase in size and making it harder to grow crops in those kinds of places. SteveBaker 17:52, 7 November 2007 (UTC)

Psychology: person A evaluates B by the evaluation of C, D, E.... for person B.

This happens quite often. Is there a name for this please? And are there any known personality traits of person A that make them more likely to indulge in this? Thanks 80.2.214.75 15:19, 7 November 2007 (UTC)

Could you give an example, or a more detailed question? I'm having a lot of difficulty understanding what concept you might be looking for. On the off chance that I've got it right, is projection the term you seek? TenOfAllTrades(talk) 16:37, 7 November 2007 (UTC)

This sounds like gossip to me! That is, making judgements about people solely based on what you've heard others say about them. 83.249.121.85 16:41, 7 November 2007 (UTC)

"Checking a job applicant's references"? -- Coneslayer 16:42, 7 November 2007 (UTC)

An example: when I was at college girl X was attracted to me in proportion to the amount of esteem that she observed other people had for me; while girl Y was attracted to me irrespective of what other people thought. I am curious about how girl X and Y may differ in personality. I have seen this in men also: I was interviewed for a job once by the boss of my future boss, and when my future boss saw that his boss was taking an interest in me, his behaviour towards me improved greatly. I imagine that this behaviour is associated with authoritarianism, in-groups and out-groups, perhaps Machiavelimism and so on.

Another example could be germans who evaluated people of the jewish faith according to nazi propoganmder, and others who were more resistant to the propoganda. Another example is here http://news.bbc.co.uk/1/hi/scotland/north_east/6273231.stm where it says women are attracted to men according to the attention they receive from other women.80.2.211.126 23:12, 7 November 2007 (UTC)

Energy

We are told that energy can neither be created or destroyed but say a person throws a ball which eventually comes a complete stop, where has that energy gone? —Preceding unsigned comment added by 195.188.208.251 (talk) 17:53, 7 November 2007 (UTC)

It all winds up as heat, thermal energy. Whenever energy vanishes from a mechanical system (throwing a ball is a simple such system), it mostly becomes heat. Someguy1221 18:00, 7 November 2007 (UTC)

Look at potential energy, and also energy in particular 'forms of energy'. it has a bit on a bouncing basketball. and further down the conservation of energyny156uk 18:02, 7 November 2007 (UTC)

Yes - and in the case of the ball, what happened was that the successive final bounces of the ball deformed the rubber that it's made of and that caused the rubber to heat up and the ball to bounce a little less high the next time - the ground too would flex a tiny bit and gain some heat at the expense of the ball. Also every time it bounced, the ball made a noise - which required some of the kinetic energy to be consumed in making the air vibrate - but the moving air has some internal friction which heats the air up a tiny bit as the sound dies away. In the end, it's turning all of that interesting kinetic energy into generalised, diffused heat. But it might take a while - we can come up with some scenarios in which it takes an INSANELY long time to finally turn all of the energy of the ball into heat. Suppose the ball landed on (of all things) a WintOGreen flavored Life Saver and crushed it. A weird property of that particular candy (called triboluminescence) would actually result in a small pulse of blue and UV light to be radiated outwards as the candy was crushed. Of course as that light is absorbed, it too will turn into heat - but a small fraction of the light would head upwards, escape from the earth's atmosphere and head out into space. It could be trillions of years before the light hits a stray bit of cosmic dust - but when it does, you just get some heat. This tendancy for everything interesting to eventually turn into heat is called Entropy and it's really rather depressing. Can we talk about something else now? :-( SteveBaker 18:15, 7 November 2007 (UTC)

Related question

If one were to invent a 100% perfectly efficient machine, would it not produce any sound, as sound would be a result of friction and wasted energy? -- MacAddct  1984 ^{(talk • contribs)} 19:36, 7 November 2007 (UTC)

Yes, exactly. (Except of course if the machine were designed to produce sound, like a loudspeaker or musical instrument.) —Keenan Pepper 19:49, 7 November 2007 (UTC)

The way intelligence grows on the "nurture" side

Hi! After studying the "nature vs. nurture" aspect of intelligence in a high school psychology class, I came up with my own "theory [in respect that I have never read or heard anything related to the ideas in this "theory" before]" on how intelligence grows on the "nurture" side of things. I know this isn't the place to post personal theories and want them to be proven or disproven, but, after thinking about this one, I thought it was a basic enough concept that it would have to have had already been proven or disproven by now --- so I am now simply looking for someone to confirm or deny this.

Okay. My "theory" is that, indirectly, the more you know, the more intelligent you are --- not simply because you know more, but because, knowing that you DO know more, we know that you have used your brain more, which is the reason you're more intelligent. I am relating this to physical fitness. Physical muscles [as opposed to the mental muscle (i.e., the brain)] grow --- along with phsyical fitness level --- as you exercise more. Why wouldn't the same be true with the brain, except with gaining more knowledge other than exercising? The brain is a muscle, too, right? And, so, using that muscle more (i.e., gaining more knowledge) would increase THAT muscle's competency too, right?

Going along with this, I know a lot of people criticize I.Q. tests, saying "Well, the I.Q. test included questions with information I just never learned before! It wasn't fair! Just because I never learned information doesn't mean I'm less intelligent!" But I criticize that criticism, with the information I posted above. Also, or people will say "Just because I didn't receive that high a level of education doesn't mean I'm not intelligent". But, again, I am trying to refute that.

And I think that the statements in the paragraph above are made and thought of because of people's emotions. I know that it isn't always people's faults that they didn't receive that high of a level of education --- and because it wasn't their fault, it would be "mean" to think a person is less intelligent because of a reason they couldn't help. But, whether or not you can help your level of education, (according to what I am thinking) the higher the level of education you have, or the more knowledge you know, the more intelligent you --- indirectly. Again, not because you learned and know more but because you used your brain --- a muscle --- more, which increased its competency.

And I do realize that, with the "nature" side of intelligence, people can still be intelligent, despite low level of education, or lack of knowledge, as their base --- or genitic factor of --- intelligence might have been high at birth. I am just saying that knowing more information is a GENERAL indication of a higher intelligence.

Again, I thought this was a basic enough concept that it had to have been proven or disproven by now. So, which is it? —Preceding unsigned comment added by Pitman6787 (talk • contribs) 19:37, 7 November 2007 (UTC)

Just giving you a few of my thoughts here. Anybody who exercises more, will grow more muscles, but only a few can become top athletes - the ones that have excellent genes. Yes, if you know more, you will get a higher result on some intelligence tests, but people differ in how much information they can gain and reproduce (and by testing this you would rather test memory instead of intelligence), and, more importantly, having a huge fund of information doesn't mean for instance improved reasoning skills or perceptual abilities, which also are considered to be important parts of intelligence. —Preceding unsigned comment added by Lova Falk (talk • contribs) 19:48, 7 November 2007 (UTC)

I'm not sure if you saw this page section: Intelligence quotient#Environment. --JWSchmidt 20:59, 7 November 2007 (UTC)

Re: education. I don't think anyone would argue that a mind well-tested as a mind sharpened. If you are in the habit of dissecting logical arguments, for example, you are going to be better at it than if you were not in that habit. The question is whether that measures what we think of as "intelligence" or not. Expanding that definition to include education makes sense in some cases, but not in others. Look at the test questions from the Army Alpha Intelligence Test (1914-1918). Try and tell me with a straight face that knowing who Rosa Bonheur is, what product Velvet Joe was the mascot for, or what a Wyandotte is measures anything other than exposure and retention of simple factual information? Those are the extreme examples, but everything else in the "informational" section falls under that category; it's entirely possible to be quite bright and just never learn where exactly the pancreas is in one's body; and on the converse it's possible to be quite dumb and know simple things like that. It's well known that total dolts can excel at bar-room trivia; that's not a measure of intelligence of any sort. So clearly some line must be drawn between being asked questions that are purely "educational" and those that are not; knowledge of miscelleanous facts is not what anyone generally considers "intelligence" to be. --24.147.86.187 01:08, 8 November 2007 (UTC)

Re:Sorting it out. We have somewhat sorted out, the answer is "it's complicated, and it's something of an artificial question." Genes provide the template for an organism which then must develop in an environment; they are not mutually exclusive categories in many respects. They are in a complicated relationship, some times more complicated than others. With very simple traits (single-point mutations) it is not too hard to untangle in most cases; when talking about more complicated genetic traits then development starts to play a big role. When talking about something like "intelligence", the exact definition of which is quite murky, then it becomes exceptionally hard to untangle, and many environmental and genetic factors start being at play. But it isn't a simple "x% this, x% that" sort of equation; it's the complexity that comes from having an organism develop, where genetic code tells individual cells what to do, but somehow we are supposed to understand complicated aggregate behavior of an entire organism. It's not that we don't know how to sort some of these things out, but sorting them out in a straightforward way has proven pretty difficult, especially if we are talking about groups that exist in complicated social dynamics that cannot be really reasonably escaped for the purposes of testing. --24.147.86.187 01:08, 8 November 2007 (UTC)

Human Evolution

Well, Heroes is on again tonight. I was just wondering if there are any clues as to how H. sapiens will evolve in the medium term. Obviously i am not expecting spontaneous levitation, telekenesis or other such nonsense - more physiologically. Are humans now capable of purposefully selecting a route of evolution to their own ends? --russ 20:13, 7 November 2007 (UTC)

The things we are evolving are likely to be small tweaks that make us better suited to our environments...not major stuff like being able to fly. One example of a "recent" evolved change has been adult lactose tolerance. Most other mammals (and humans as recently as the ancient Egyptians) are lactose intolerant as adults. When we started farming and milking goats and cows, there was a clear advantage for humans who were able to digest milk. So we started to evolve lactose tolerance and the lactose intolerant people started to decline in numbers. However, in our modern world, it seems very unlikely that you could die without leaving offspring just because you are still lactose intolerant - so it seems like that genetic change hasn't spread throughout the population yet. It wouldn't surprise me if we started to adapt in ways that helped us in the modern world...but genetic changes take thousands of years and our environment has changed so dramatically in just the last 100 years that we havn't had time to evolve to support that change. If I had to go out on a limb and predict something, I'd suggest that we might evolve a way to avoid obesity. That kills off a lot of younger people and certainly reduces their attraction to the opposite sex - so it ought to have a serious impact on reproductive capability. If a gene came along at random that helped avoid that problem then I imagine it would sweep the western world in a matter of just a few thousand years. But you can't KNOW that this will happen.

As for whether we are purposefully driving evolution - in a sense, we always have. By being selective with whom we mate with - we make that choice quite a lot. In terms of using gene replacement therapy we MIGHT make a change. As a matter of fact though, it's possible that we're inadvertently screwing things up rather badly. Think about this. What happens if a married couple want a baby and can't have one? They go to the scientists and magic wands are waved, incantations spoken and (in quite a few cases), a baby is the result. In fact, multiple babies may result in an unnaturally large percentage of the cases. So if there were a genetic cause for infertility that would normally be strongly selected against, we could quite easily accidentally make it not only NOT be selected against - but because of the possibility of multiple births due to fertility drugs, we might even make genetic infertility become a trait that tends to increase over time. That's pretty worrying - but it's exactly the kind of thing that we'd be just stupid enough to do.

SteveBaker 20:27, 7 November 2007 (UTC)

The ancient Egyptians were lactose intolerant? Them and 70% of adults alive today. Algebraist 20:41, 7 November 2007 (UTC)

That 70% seems very high. Even more so are some of the population-specific numbers -- none of the many various Asian Americans I know have ever identified themselves as lactose intolerant, and I've certainly seen them consuming cow by-products before. jeffjon 21:21, 7 November 2007 (UTC)

If milk causes such problems in so many people, why is it so popular? Do only 30% of the population drink milk? Surely people wouldn't drink it if they were afflicted? --212.204.150.105 21:18, 7 November 2007 (UTC)

The degree of lactose intolerance is highly variable in both its severity and its age of onset. Some people don't begin suffering until their 30s or 40s, and even then, many lactose intolerant individuals can drink a cup or two a day without suffering any symptoms. Someguy1221 21:31, 7 November 2007 (UTC)

70% has got to be *WAY* too high. The article says that there are multiple causes - we're talking here about people who are congenitally lactose-intolerant as adults - not people who are that way because of diseases. But even so, there simply is no way that number can be right in any of the parts of the world I've lived in. Out of all of the people I know well enough to have been able to tell - at least 20 or 30 people - I can only think of one who suffers from that condition. If it's 70% then the number should be 15 to 20 of them...there is no way I can not know those people that badly. We've had every one of them over to our home for dinner on multiple occasions - my wife's French - everything has cream sauces and such. No - it's not 70% in Europe or North America. It's gotta be way less than 10%. 70.116.10.189 23:38, 7 November 2007 (UTC)

If 70% seems way too high to you, it’s because of which people you’re typically exposed to. The mutation that allowed lactose to be digested by adults happened quite recently (on an evolutionary scale) somewhere in northern Europe. So if you hang out around people of primarily northern European descent, then the 70% is going to seem high to you. But if you lived in China or Thailand, that figure would seem very low to you. MrRedact 00:32, 8 November 2007 (UTC)

70% was for the whole world. See Image:LacIntol-World2.png. Someguy1221 00:34, 8 November 2007 (UTC)

70% for the world seems right when you factor that there are two large groups that traditionally had lactose-intolerance issues - Africans and Asians. There are a hell of a lot of Africans and Asians in the world, compared to Europeans which have less of an issue traditionally. Americans have a far, far lower rate of lactose intolerance - probably due to various worldwide cultures intermixing genes to allow them to spread faster. Kuronue | Talk 04:54, 8 November 2007 (UTC)

Historically, the idea of humans "purposefully selecting a route of evolution to their own ends" has often been a bad idea, especially with Nazi eugenics. MrRedact 00:49, 8 November 2007 (UTC)

Of course, if we have eliminated natural selection by using fertility clinics, that makes genetic research that much more important. It seems to me that if we want to survive as a species, eventually we are going to have to manipulate our genes, either before or after we are born. 68.231.151.161 01:49, 8 November 2007 (UTC)

I'm not sure that we need any help on that. See also Population, Carrying capacity, Sustainability, and Earth. I think the better question is why are we doing so well as a species, and at what point should we stop trying to let people live longer. All things considered, we're simply going to run out of physical space in which to fit everyone. --slakr^\ talk / 04:40, 8 November 2007 (UTC)

Some argue that humanity’s ecological footprint already exceeds one Earth.[4] But there’s no problem with still trying to let people live longer, as long as we simultaneously reverse the population explosion through voluntary population control measures such as improving access to family planning and reproductive health care and information, eliminating incentives to have larger families, and public education about the consequences of continued population growth. MrRedact 05:21, 8 November 2007 (UTC)

Special Wheel Supported on the Lower Rim

I remember seeing somewhere a wheel that was supported on the rim below the wheel's center point. The vehicle using the wheel had no axles. I assume the rim at the point of support had some kind of bearings. The wheel had nothing inside the rims. This had the benefit of lowering the vehicle's center of gravity. Can anyone point me to a reference for this arrangement? ThreeE 20:54, 7 November 2007 (UTC)

Have you tried Hubless wheel? --TrogWoolley 22:31, 7 November 2007 (UTC)

Perfect. Sbarro (http://www.burningart.com/meico/moto/sbarro/) was the designer I was looking for. Many thanks. ThreeE 23:38, 7 November 2007 (UTC)

Why is the waste disposal system the same as the reproductive system?

Not the same, biologically speaking, but using the same body parts. Why is it like that? Do you peeps think it has some kind of evolutionary function or it's merely a bad design that just evolved that way because it works without any major malfunctions (although there are sometimes malfunctions). 64.236.121.129 21:33, 7 November 2007 (UTC)

Er, not sure what you mean. In mammals the reproductive system is separate in all respects except for the dual-purpose male phallus. In other vertebrates the two systems do vent at the same place, the cloaca.--Eriastrum 23:12, 7 November 2007 (UTC)

And the reason for that arrangement is basically that the original chordate body plan consists of a muscular tube with a hole at each end. Any elaborations on that, such as limbs or extra orifices, are later additions, and are unlikely to occur unless there has been some selection pressure for them at some point. We can thus deduce that, for example, at some point in the evolution of placental mammals there was an evolutionary advantage to females having a separate vaginal opening. Figuring out what the cause of the pressure might've been is left as an exercise for the reader. —Ilmari Karonen (talk) 01:12, 8 November 2007 (UTC)

You don't know what I mean? Drop your pants and see where your sexual organs are, and where your waste disposal organs are. DUH. Come on, this ain't rocket science peeps :). 64.236.121.129 15:31, 8 November 2007 (UTC)

I think this argument is questionable. Sexual reproduction exists outside of phylum Chordata and presumably predates it, so one might as easily discover that the development of a spine was an elaboration on some proto-tubeworm's reproductive system. I don't know what the relationships actually were, but they are presumably very, very old. Dragons flight 03:10, 8 November 2007 (UTC)

That could well be; the point I was making is that the default condition inherited from our proto-chordate ancestors is "one hole in front, one in the rear". That our present body plan, in many ways, still resembles this ancestral model should not be surprising; rather, it's the deviations from this basic body plan that require an evolutionary explanation. Presumably, then, the reason the human reproductive organs are close to the anus is that they used to share the same opening (the cloaca), and that there hasn't been sufficient evolutionary pressure to move them any further from each other than they are. —Ilmari Karonen (talk) 22:09, 8 November 2007 (UTC)

I Cannot think of a good reason why poop is RIGHT by the fun stuff! PS dude above, MAMMALS: NOT SEPERATE at all...Hands and feet,..now that's seperate —Preceding unsigned comment added by 76.168.69.208 (talk) 02:09, 8 November 2007 (UTC)

I'm actually curious as to this as well. Not just humans - most female mammals that I'm familiar with have both vaginal and anal openings within a few inches of each other. Considering how irritated the vaginal opening can get when feces is accidentally introduced (personal experience here - always wipe front to back!), this seems counter-intuitive. Kuronue | Talk 04:58, 8 November 2007 (UTC)

Perhaps, there were some advantages in the prenatal development of these organs that let it evolved in this way. See Development of the urinary and reproductive organs. What about digestive and respiratory systems? They seem to have some overlaps as well. --Vsion 05:43, 8 November 2007 (UTC)

Because this enables humans to cover for most eventualities with just one item of underwear.--Shantavira|^{feed me} 09:07, 8 November 2007 (UTC)

I think it is merely just a bad evolutionary design that stuck merely because it worked satisfactorily, although it is anything but ideal. 64.236.121.129 15:36, 8 November 2007 (UTC)

You shouldn't think of evolution as a design. No men in white suits mulling over the latest design models for the new species. Evolution happens by accident, and for things to change a mutant child must be born whose genetalia are farther removed from their bowels. Maybe move them up to the stomach? It'd be more convenient for child birth. (Every time I think of it, an image pops into my head from the original Alien movie) Man It's So Loud In Here 21:48, 8 November 2007 (UTC)

Looks like a devine example for unintelligent design
--Cookatoo.ergo.ZooM 19:21, 13 November 2007 (UTC)

series of vaccine for rabies

Following an encounter with a rabid fox, I received a series of vaccine for rabies as treatment. A month later I was planning to donate blood at the local Red Cross. Prior to my scheduled time at the Red Cross, I had contacted a physician who had said that it was okay for me to donate my blood. However, the people at Red Cross thought differently and told me that I have to wait up to one year to donate again. Do you know how long a person who has received the series of vaccine for rabies needs to wait and why?Pumpkin68 21:37, 7 November 2007 (UTC)

Time limits are pretty much arbitrary. The (U.S.) Department of Defense concurs with your Red Cross information: they require a wait of 1 year before blood donation if the rabies vaccination was given for rabies exposure (an animal bite, for example); there is no wait if the rabies vaccine was given for other reasons, and the donor is symptom-free. Thus the wait seems to be dictated by the animal bite and not the vaccine. - Nunh-huh 22:27, 7 November 2007 (UTC)

Are other mammals attracted to female mammary glands?

Human males are attracted to girls with big boobs. Is there any scientific evidence that shows other mammals attracted to mammary glands? Like maybe a male Bull poking its nose against a cow's big puffy thing at the bottom (utter? whatever you call it). 64.236.121.129 21:45, 7 November 2007 (UTC)

Not really what you're looking for at all, but slightly related: Koko, the female Gorilla that liked to see and touch human nipples (both male and female). jeffjon 21:57, 7 November 2007 (UTC)

It is my understanding that the male attraction to breasts is part genetic, part culturally trained. The genetic part I always assumed worked on the basis that larger breasts made a female look like they would produce enough breast-milk to rear a large family - thus making them more attractive to the males who wish to spread their seed. Now i cannot say this is scientific, i probably heard it some place and took it as true, and i'm sure there'll be science that shows breast-size has little impact on the amount of breast-milk a woman can produce, but that has been my idea. If this angle is correct then other animals will have an interest in any female/male attributes that show-off to the group/pack that they are fertile/strong, whatever the other sex wishes them to be. So things like Peacocks showing off their fantastic tails to attract peahens (lots of birds have coloured plumage to attract other birds) or the male lions fighting for pack-dominance because that will often lead to them having the best female-mates. Look at sexual attraction ny156uk 00:41, 8 November 2007 (UTC)

I think I can say with a great deal of certainty that other mammals are not attracted to female mammary glands. Check out our cleavage article. And be sure to read the linked citations too (actual pages from the book, I think). --Cody Pope 02:32, 8 November 2007 (UTC)

I think I've heard it speculated that the phenomenon of enlarged female breasts in homo sapiens is an example of an evolutionary arms race, or more specifically, runaway evolution. (This is basically what ny156uk was saying.) —Steve Summit (talk) 03:16, 8 November 2007 (UTC)

All other mammals are attracted to mammary glands. That is the single defining behaviour of mammals (the clue is in the name!) However, in most mammals the attraction wanes considerably on weaning. As far as we can tell, only adult humans consider breasts sexually attractive. Incidentally, investigating how and why mammals find breasts attractive (for suckling, not for staring at in Playboy) and the sensory mechanism through which that attraction is mediated, is what I do for a living. We have some interesting and surprising findings, but I'm afraid I can't tell you what, is it is not yet published. At work today I spent the afternoon timing babies crawl around on naked female breasts. Its a tough job! Rockpocket 09:07, 8 November 2007 (UTC)

Cats which like milk would be attracted to the smell of milk from a lactating female human. Edison 13:11, 8 November 2007 (UTC)

Unweaned mammals (meaning young which still want to nurse) don't seem to care where the meal comes from, as long as they get fed. Simple experiment: Have a post-puberty female human pick up a nursing puppy or kitten. Expected result (because I've seen it many times): If allowed, the puppy or kitten will attempt to nurse. A hungry baby mammal just doesn't care who or what owns the teat; he/she/it just wants a meal. The news is full of cross-species nursing. Even our own legends (founding of Rome) are full of it. -SandyJax 16:13, 8 November 2007 (UTC)

That isn't entirely true, the literature shows that the smell of milk from different species does not always promote suckling in others, irrespective of Romulus' experience. For example, its the smell of 2-methylbut-2-enal in rabbit milk the promotes suckling in rabbits. Human, cat or mouse milk does not promote suckling in rabbits because, presumably, they do not express 2MB2 in their milk. The suckling promoting odors of other mammals have not yet been identified. Rockpocket 19:20, 8 November 2007 (UTC)

I once read a story in the newspaper about a woman who breast-fed a litter of orphaned kittens. That is about all I have to contribute to this thread. --Kurt Shaped Box 20:04, 8 November 2007 (UTC)

It seems that enlarged mammae - at least in other mammals - are the result of ovulation having taken place. As such they are a prime sign of fertility, which, in mammals including homo sapiens, is periodic and not constant. So, the attraction of bigg(er) boobs makes evolutionary sense as it maximises the offspring per copulation.
--Cookatoo.ergo.ZooM 19:43, 13 November 2007 (UTC)

a reaction is either oxidative or non-oxidative, never inbetween

AGEs can be formed via oxidative pathways (e.g. carboxymethyllysine [CML] and pentosidine), via non-oxidative pathways (such as pyrraline), or from highly reactive dicarbonyl precursors, such as glyoxal, methylglyoxal and 3-deoxyglucosone (3-DG). - a reaction is either oxidative or non-oxidative; how can they give three categories then? The dicarbonyl precursors either react oxidatively or they don't... --137.120.53.67 21:47, 7 November 2007 (UTC)

What's an AGE? Delmlsfan 23:42, 7 November 2007 (UTC)

Could be Advanced glycation endproduct, what you get when you cook carbohydrate with protein. Graeme Bartlett 01:05, 8 November 2007 (UTC)

Amnesia

What is the name of the illness where the sufferer experiences amnesia every few minutes? Keria 22:23, 7 November 2007 (UTC)

I forget. -- Coneslayer 22:38, 7 November 2007 (UTC)

Anterograde amnesia. Someguy1221 22:39, 7 November 2007 (UTC)

effect heat has on rubber

$<math>Insertformulahere$</math>

In oxygen atmospheres, combustion is the usual result. Delmlsfan 23:44, 7 November 2007 (UTC)

If you can exclude oxygen, it will give off hydrocarbon gasses and liquids, and leave behind some kind of charcoal. Graeme Bartlett 01:02, 8 November 2007 (UTC)

Vulcanization? Heat equation and heat transfer will get you started on how the energy transfers along the bulk, but your relevant parameters ("k") are going to be temperature dependent and sample deformation will be an issue. At low temperatures, rubber becomes frangible (yet another way to have fun with liquid N₂). At some temperature depending an what you mean by "rubber" (i.e. the stuff that comes out of the tree or any of several commercial products and colloquial usages meaning materials having the characteristic bouncyness of rubber), your sample will melt. Very shortly thereafter, it ceases being rubber, as above. Eldereft 05:44, 8 November 2007 (UTC)

November 8

cells

what would happen if you place a blood cell in a hypertonic solution —Preceding unsigned comment added by Dmx123 (talk • contribs) 00:37, 8 November 2007 (UTC)

The reference desk it not for answering homework questions, but if you can't figure this one out on your own, you should read osmotic pressure. Someguy1221 00:49, 8 November 2007 (UTC)

... or Osmosis or Diffusion. --slakr^\ talk / 04:35, 8 November 2007 (UTC)

... or better yet, hypertonic. (The article answers this very question.) -- 20:21, 8 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.105 (talk)

navel

hey how come for some people when they're fingered in their belly button, it hurts and for others it tickled them?Jwking 01:00, 8 November 2007 (UTC)

Because some people don't know how hard to poke, and just stab you with their finger. HYENASTE 01:17, 8 November 2007 (UTC)

Reception of off air frequency standards

May be a stupid question, but why, when receiving, do you need a local oscillator to phase lock to the incoming signal? Only reason I can think is that the transmitted signal is not constant in amplitude. Why cant you use the incoming frequency dorectly? Also, why do you need a quartz Xtal osc to be locked to the incoming frequency, won't a normal vco do? —Preceding unsigned comment added by 79.76.246.62 (talk) 01:42, 8 November 2007 (UTC)

It's for FM reception. The radio signal is varying slightly up or down in frequency depending on the amplitude of the sound wave it's trying to transmit to you (Frequency Modulation). You tune the radio's local oscillator to the nominal center frequency and it's easy to produce an audio signal that's proportional to the difference in frequency of the local oscillator and the radio signal. SteveBaker 01:59, 8 November 2007 (UTC)

Er, no its AM. [5] —Preceding unsigned comment added by 79.76.246.62 (talk) 02:20, 8 November 2007 (UTC)

You need a very low bandwidth. Typically the signal will be 5kHz wide, at a frequency of 10MHz. A VCO is no where near stable for this and will drift off in a few minutes. You can see this on old cheap shortwave radios, which will need retuning every so often. The crystal oscillator is much more stable. A VCO locked to a crystal is one way to get flexibility. Another important thing for a frequency standard is low phase noise. The best way would be to have a narrow crystal filter at 10 MHz, but even so the ionosphere causes fading and phase shifts. For 60kHz standard a LO would not be needed. Graeme Bartlett 05:57, 8 November 2007 (UTC)

So you can use the ultra stable 60 kHz freq directly (or multiplied up to 1 MHz or 10 MHz or whatever)? Is that what your saying? If so, why do most designs use a local oscillator locked to the incoming frequency? —Preceding unsigned comment added by 79.76.246.62 (talk) 12:06, 8 November 2007 (UTC)

See Superheterodyne receiver. Changing the frequency of the local oscillator is what tunes the radio to a station. Its frequency is beat against everything coming in from the antenna. The resulting harmonics are filtered for the intermediate frequency, 455kHz in the case of AM. A big advantage to this system is that from there on the amplifiers need only pass the one relatively low frequency. I don't know what you mean by a crystal oscillator locked to the incoming frequency, but it has been a long time, so please clarify. --Milkbreath 03:33, 8 November 2007 (UTC)

Crystal control is absolutely not needed in an AM radio. I have owned several old AM radios which would stay tuned to a station for a year or more without re-tuning. Older car radios had pushbuttons which mechanically rotated a tuning cap to the desired stations, and did not need re-tuning for years at a time. Edison 13:10, 8 November 2007 (UTC)

For a frequency standard, a Local Oscilator is not stable enough. You would need to down convert to the intermediate frequency, filter, and then up convert to the original stable frequency to get the reference. On HF frequencies around 10 MHz drift is ten times bigger than it is on the AM band around 1 MHz that you get on an old car radio. If you just want to listen to the time pips all this extra stability is not needed, you just need to keep the radio tuned to the station. Graeme Bartlett 20:38, 8 November 2007 (UTC)

I think the answer is that the off air frequency references have excellent long term stability, but are subject to the vagaries of radio reception such as : noise, timing uncertainty due to reflections from the ionosphere etc, and unwanted amplitude modulations, breaks in reception etc. OTOH, Local crystal oscillators can be made to have excellent short term stability and low phase noise etc but are subject to long term drift from component aging. Put the two together and get the best of both worlds!

Minerals

Is it possible to make a mineral (in this case a molecule containing iron) magnetic by running an electric current through it, or around it? I have reference here to the specific mineral asbestos, or one of its several 'subspecies'?76.182.3.188 01:56, 8 November 2007 (UTC)

Very few minerals can be magnetized in a way such that they remain magnetic after the inducing field is removed. See Magnetization. A good many minerals, including some without iron, such as salt, can be made to give a diamagnetic response while the inducing field is present, but I do not think asbestos is one of them (but I'm not certain about that). Cheers Geologyguy 03:03, 8 November 2007 (UTC)

Most minerals do not conduct, so you cannot easily run a current through them. In the case of asbestos it is a good insulator so it will not conduct at any reasonable voltage. If you ran a current around it you would have an electromagnet. The atoms in the mineral would respond in some way, but most have no strong response. A few Iron minerals may respond with ferromagnetism and even be magnetised as in Magnetite Graeme Bartlett 05:52, 8 November 2007 (UTC)

See Lodestone, a mineral (Fe3O4) some samples of which are found in the ground as natural magnets. The Wikipedia article does not say it, but other sources say the magnetism may result from lightning striking the mineral [6] [7] [8]. Edison 13:07, 8 November 2007 (UTC)

microwave hyperthermia

any reason not to heat someone up (their whole body to 104 F - 107 F) with a very high tech microwave (in order to generate a healing fever)? It penetrates and is the same frequency as cell phones... —Preceding unsigned comment added by 76.168.69.208 (talk) 02:02, 8 November 2007 (UTC)

Microwaves do not heat everything uniformly, and in particular they will heat organs with a high water content more rapidly. Of special concern are the eyes where high levels of microwaves can promote cataracts and other damage.

On the more general point, I'm not sure that heat is necessarily helpful in fighting disease. Fever is one of a myriad of reactions the body produces to combat disease, but an externally produced hyperthermia might be more detrimental than helpful since it wouldn't necessarily be accompanied by the same suite of immune responses as a natural fever. Dragons flight 02:25, 8 November 2007 (UTC)

Also note: Wikipedia does not give medical advice. Anyway, the Hyperthermia article states that temperatures above 104 degrees Fahrenheit are "life threatening". I wouldn't reccomend it either, unless you know what you are doing, and I would get a second opinion (from a qualified professional) either way. I also have never heard of inducing a fever to heal by this method (or any), as fevers are caused naturally by the body as part of the immune response. SmileToday☺(talk to me , My edits) 02:28, 8 November 2007 (UTC)

He might have gotten this from last week's episode of House, in which a portion of a treatment for an individual was artificially raising his body temperature. Someguy1221 02:39, 8 November 2007 (UTC)

Microwave heating of smaller regions of the body to fever-range temperatures has been tested for various therapeutic purposes. If you're envisioning putting the entire body in a microwave oven (even a high-tech one) to heat the entire patient at once, you're out of luck. Per Dragons flight, you would get dangerous local heating effects that are very difficult to control. There are other, lower-tech methods that are just as effective. Where I have seen microwave heating employed is to do rapid, local thermal ablation of smaller volumes—a microwave antenna is inserted into a solid tumour, and the temperature elevated high enough to 'cook' the tissue.

If you go to ClinicalTrials.gov and search on the term hyperthermia, you'll find a number of trials – mostly for cancer – that are testing the use of whole-body hyperthermia as a way to sensitize the body to radiation or chemotherapy or to potentiate the immune system's response to malignant tissue (e.g. [9], [10], [11]). Techniques that have been used to achieve hyperthermia include induction heating, warm wax immersion, hot water blankets, and radiant infrared heating. Patients under general anasthesia can also be treated using extracorporeal hyperthermia—blood can be drawn from the body, warmed externally, and returned to circulation. TenOfAllTrades(talk) 12:45, 8 November 2007 (UTC)

I'll note that in non-medical contexts, there have been various suggestions to replace a home's heating system with a (low powered) microwave generator. Instead of heating the air, you heat the body directly. Supposively, this would save on energy costs. A quick Google search turns up [12]. -- 20:25, 8 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.105 (talk)

Why is water transparent?

Why is water transparent? I did some searching, and the reason for this is because water is transparent to the visible spectrum of light. But why does it exhibit this property? Does it have something to do with its hydrogen bonds that are responsible for so many of its other special properties? Acceptable 02:37, 8 November 2007 (UTC)

There’s some explanation of this in absorption spectrum. Which frequencies a water molecule can absorb depends on what possible quantum states the molecule has. The frequencies of photons that the molecule can absorb correspond to the possible differences in energy between pairs of states. The ratio of a difference in energy level to the corresponding freqency of light is known as Planck's constant. MrRedact 03:20, 8 November 2007 (UTC)

I should point out, water is slightly blue. Malamockq 03:28, 8 November 2007 (UTC)

Consider checking out Color of water. --slakr^\ talk / 04:32, 8 November 2007 (UTC)

Plasmon frequency? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:15, 9 November 2007 (UTC)

Eyeballs are mostly made of water. This would affect what light could be seen.Polypipe Wrangler 21:24, 13 November 2007 (UTC)

Tectospinal tract

Is it safe to conclude from this picture that the superior colliculus is connected with the inferior colliculus through the tectospinal tract? Lova Falk 10:29, 8 November 2007 (UTC)

There are some axons that go from the superior colliculus to various brain locations (tectobulbar axons) but I think the vast majority of the axons in the tectospinal tract first go anterior (ventral) and then cross the midline before descending past the level of the inferior colliculus. A good neuroanatomy textbook will have a figure for the tectospinal tract showing a series of brain cross-sections, one at the level of the superior colliculus, one at the level of the inferior colliculus and several more going down to the spine. This is the best I could find online (and it is not very good). --JWSchmidt 18:51, 8 November 2007 (UTC)

Point and shoot digital camera

Is it true that camera manufacturer deliberately introduce shutter lag into PS digital camera to "encourage" their clients to buy the much much more expensive DSLR camera instead. 220.237.184.66 12:06, 8 November 2007 (UTC)

Unlikely, as not all point-and-shoot manufacturers have a DSLR in their lineup. One reason that comes to mind is that contrast-detection autofocus is slower than phase-detection autofocus. It's also possible that "something" has to be done to the CCD or CMOS sensor before taking the shot, if the sensor has been used for a live preview. For example, CCDs may accumulate charge that needs to be cleared. Since DSLRs generally do not have a live preview, they can keep the sensor ready to shoot. Maybe people know of other factors that I'm not thinking of. -- Coneslayer 13:31, 8 November 2007 (UTC)

Point-and-shoot cameras are slower because they use contrast detection rather than phase detection autofocus, and because they usually have a less-powerful focus motor to increase battery life. You can test this by pre-focusing a point-and-shoot: once it's focused, it's actually faster than a DSLR at taking the picture, because the DSLR needs to get the viewfinder mirror out of the way. --Carnildo 22:46, 8 November 2007 (UTC)

Inelastic collision

About Inelastic collision As we know that in inelastic collision the initial and final momentum,total energy are conserved but kinetic energy is not conservsed.this is why ,why kinetic energy is not conserved .Plz explain the example of the collsion of cars.also mentioned it that after collsion the two cars come to rest then how is initial and final momentum the same , as they are moving with a speed before collision .thanx ........usman —Preceding unsigned comment added by Star33 2009 (talk • contribs) 13:15, 8 November 2007 (UTC)

It may be useful to compare inelastic collisions with elastic collisions, whereby kinetic energy is conserved (see the first two sentences of that article, then contrast with the lede in inelastic collision). As for the car collision, bear in mind that physics is not nearly so concerned with "speed" as it is with velocity, and consider that the momentum of the two-car system is what's being conserved, not the momentum of the two individual cars. — Lomn 14:00, 8 November 2007 (UTC)

I actually ran a little experiment on this. Kinetic energy is always conserved as a physical law- if it's not, you haven't included everything in the system. So we have to know where the energy of collision goes to. I modelled this with a spring system, as springs are a good approximation for any interaction and well-established in the interaction of particles. So then we have energy initial = energy final, or $KE_{1}+KE_{2}=KE_{1,2}+E_{\textrm {spring}}$. Now note that the energy of the spring includes both the spring potential energy, 1/2kx^2, and the kinetic energy of particle 1 and 2 oscillating against the spring. It is what is called a simple harmonic oscillator. So now

$KE_{1}+KE_{2}=KE_{1,2}+KE_{1,2{\textrm {spring}}}+1/2kx^{2}$,

and so energy is conserved. The spring model has some consequences: it implies both that there are oscillations between the two particles after collision and that there is a non-zero collision time with finite acceleration. In the intro physics lab which I TA, the data showed the finite acceleration which agreed to good approximation with the theoretical acceleration of the spring (a linear differential equation - if you want me to show you how it is solved, please let me know), but no oscillations after collision. This is because the oscillations are quickly damped out as heat (another differential equation), which should also be measurable with a calorimeter, but I haven't tried this experiment. Energy is still conserved, as heat is another form of energy for which we can account.

For your second question, note that momentum is a vector quantity, so it has both magnitude and direction - that should put you on the right track. SamuelRiv 14:11, 8 November 2007 (UTC)

Momentum is a vector - but kinetic energy isn't.

If you crash two very stiff objects together (two billard balls for example) then they bounce off and the sum of the kinetic energies of the two balls is almost exactly the same before as after. When you whack two cars together, the energy is absorbed in bending and tearing metal and plastic - so they don't bounce off much - there is no kinetic energy left, it all turned into heat. If you bounce two rubber balls together, the result is somewhere between the two extremes. KINETIC energy is not conserved in real-world collisions - but TOTAL energy is. SteveBaker 03:38, 9 November 2007 (UTC)

camera pixel resolution

What is the engineering standard for stating the number of pixels that make up a camera? The actual number of individual sensors, i.e., the number of rows of sensors times the number of columns of sensors on the chip, or the number of different areas of a picture that are focused onto a single sensor or single small group of individual sensors in sequence to build the whole picture? Clem 13:54, 8 November 2007 (UTC)

Megapixel ratings are just a description of the number of sensors. The fact that more goes into a good picture than that rating alone is one of the reason the rating system is seen as being somewhat deceptive. As the page points out, in cameras this is even more deceptive, since each sensor generally registers only one color, and so the final image resolution can be easily a third less than the MP rating. --24.147.86.187 15:03, 8 November 2007 (UTC)

Here is an example of a sensor with three layers one for red, one for green and one for blue.[13] Along with the powerpoint that outlines the old technology and explains this new technology.[14] It is marketed as a 4.5 Megapixel CMOS direct image sensor with a maximum picture size of 1420 x 1064 x 3 matrix as seen in the HanVision HVDUO-5M digital camera. David D. (Talk) 23:05, 8 November 2007 (UTC)

The megapixel count on a camera is the number of pixels in the image it produces. The actual number of light-sensing elements depends on the sensor technology used and the relative influences of the marketing and engineering departments. Sensors using the Bayer pattern and the related CMYK pattern will typically have as many single-color sensor elements as there are pixels in the output image. Cameras using the Foveon sensor pattern can have one-third as many full-color sensor elements as there are pixels; cameras using Fuji's Super CCD pattern have one-half as many songle-color sensor elements as there are pixels. Cheap high-megapixel cameras will use a small sensor and scale the image up: a 20-megapixel camera might use a 5-million-element sensor and use interpolation to produce an image with more pixels. --Carnildo 23:35, 8 November 2007 (UTC)

Old cars carbon emissions

How does the average carbon output of a 1980 1.4l petrol engine compare to a recent one? I heard statistics saying that 20% of the oldest cars represent 60% of total emissions. Is this correct? In view of these statistics some countries want to tax (or are already doing it) old cars. If we add the carbon output of producing a new car and disposing of the old one to the equation, is it still so favorable to buying a new car vs. keeping an old one running longer? Should we add to this the carbon output necesssary to produce enough wealth to buy the new car or is this irrelevant? Thank you. Keria 14:06, 8 November 2007 (UTC)

Please be sure to distinguish pollution from carbon emissions. Older engines emitted far, far more pollution (unburned hydrocarbons, carbon monoxide, and the like) but the amount of carbon ultimately emitted is a strict function of the fuel economy of the car. Your 1980 1.4L car is probably emitting much less carbon per mile than my 2003 4.2L Audi (which averages about 25 miles/US gallon).

Atlant 17:20, 8 November 2007 (UTC)

You only have to compare fuel consumption numbers - that's a pretty fair comparison because the amount of CO2 you get out of a gallon of gas is about the same no matter how you burn it. My 2007 MINI Cooper'S with a 1.6l engine manages 7.5l/100km city and 5.3l/100km highway. A 1986 Honda Integra (pretty similar in size) also had a 1.6l engine and manages 7.8l/100km city, 6.8l/100km highway. So what gives? We don't do much better now than we did then...well, the MINI manages 170hp - the Integra managed about 108hp. What's happening is that we're getting more power out of engines than we used to. So whilst the consumption of a 1.6l engine isn't much better than it always was - we're able to stick a 1.6l engine into a car that would have required a 2.5l engine 20 years ago. Having said that, my old 848cc 1962 Mini manages 5.1l/100km on the highway - fractionally better than the 2007 version - but the 1962 car only has 37hp and could only manage a top speed of 72mph - the 2007 car goes MORE THAN TWICE AS FAST on the same amount of gas. SteveBaker 03:24, 9 November 2007 (UTC)

Ladder to Space

There's this infinitely tall ladder in my backyard. When I climb three or four feet and let go of the rungs I obviously fall back down to the ground. What is the minimum distance I would have to climb so that when I let go of the rungs I would never fall back down to the ground? (I think the answer is 22,240 miles where I would join all the geostationary artifical satellites of the Clarke Belt, but I'm not sure. Orbits, and rocket science in general, confuse the bejeezus out of me.) Sappysap 14:08, 8 November 2007 (UTC)

You might want to check out Space elevator. -- Coneslayer 14:17, 8 November 2007 (UTC)

It'd be geostationary orbit altitude, but only if you're also at the equator. Climbing a ladder ascending vertically from New York will not put you in a stable orbit at that altitude; you'd have to go higher. Climbing a ladder from the North Pole confers you no velocity and you'll drop from any altitude. I'm guessing the tangent of latitude is relevant to exactly how high you've got to go, but I'm not sure. — Lomn 14:24, 8 November 2007 (UTC)

Irrelevant Post Ahead: I just have to say, that Space Elevator article is extremely fascinating. Beekone 14:49, 8 November 2007 (UTC)

That is true. See Coriolis effect. We can calculate the height needed to get you in orbit - the thing about a ladder is that it's rigid, so your angular velocity at the top of the ladder is equal to the angular velocity of the earth at that latitude, so your orbit will only occur at a geosynchronous distance: see Geosynchronous orbit derivation. SamuelRiv 14:52, 8 November 2007 (UTC)

Where's a mathematician when you need one? Say your ladder is at 40 degrees north latitude. You will have to climb up to where your speed is the geostationary orbital speed. This will be higher than if your ladder were at the equator. When you let go, you will move toward the earth until you reach the geostationary altitude where you'll stay until perturbations mess things up. I'm sorry, but I don't feel like deriving the formula for all that, the relationship between angular velocity, altitude and latitude. Where's that mathematician? There are guys who can do this sort of thing in their head. --Milkbreath 17:13, 8 November 2007 (UTC)

Perhaps they're all here?

Atlant 17:17, 8 November 2007 (UTC)

Right. I had a chance to think about this just now while watching a Labrador retriever do his business (hardly a Newtonian anecdote, eh?). The only way you'll be able to let go of the ladder and just stay there is if the ladder is at the equator. So, the nerds are off the hook. (I suspect that the answer to my pointless question above is a straight line tangent to the earth at a geostationary point above the equator.) --Milkbreath 17:41, 8 November 2007 (UTC)

Not quite - there are important consequences when you get far enough out where the rotation of the Earth is too fast for gravity and you get vertical components of the coriolis effect. Integrate across the length of the ladder accounting for atmospheric effects and you'll get a mess. The ladder itself needs a counterweight to make it stable, which is why the space elevator needs such a large counterweight mass. Oh, and the math for latitude at angle phi just needs a sine term, sin(phi), to multiply through. See the formula at Coriolis effect. SamuelRiv 20:43, 8 November 2007 (UTC)

Blaise Gassend computed whether, where and how hard an object falling from any level on an equatorial elevator will hit the ground. —Tamfang 18:49, 9 November 2007 (UTC)

Answering the actual question

We were not asked how high you would have to climb on the ladder in order to enter geostationary orbit. We were asked how high you would have to climb in order to never fall back down to the ground. Which means that any stable orbit would do.

Since the atmosphere has no sharp outer boundary, there is no specific altitude above which you have to orbit in order for orbital decay due to atmospheric drag to become negligible. However, I will assume for simplicity that a distance of 8,000 km above the Earth's center (that's roundly 1,600 km or 1,000 miles above the surface) is what you need to achieve. So you want to be in an orbit with its perigee at that distance and its apogee at the point where you jump off the ladder.

The answer clearly depends on your latitude. If the ladder is at the North or South Pole, it doesn't matter how high you climb: the ladder is simply rotating around its own axis and that doesn't put you in orbit, so you'll always fall back to Earth. But if the ladder is at latitude L and you climb to a distance A above the Earth's center, then you are moving horizontally in a circle of circumference 2 pi A cos L, completing one circle per sidereal day. From here on I'll suppress units; numerical values are based on distances in km, times in seconds, speeds in km/s, etc. Then your speed is V = KA where K = (2 pi/86164) cos L.

Now, using the formulas on this page with some changes of variable names, the orbit's apogee and perigee distances A and P (from the center of the Earth), and the apogee speed V, are related by

V² = G M (2P/(A(A+P))

or in other words

V² A (A + P) = 2P G M

where G is the gravitational constant and M is the Earth's mass, and the value of GM is known to be 398,600. But in this case we also know that V = KA, so we have

K²A³ (A + P) = 2P G M

and since all the other values are known (for a specific latitude), we merely have to solve this for A. As it reduces to a quartic equation, this is not easily done by algebra, but it can be solved numerically by a simple computer program.

For example, suppose your backyard is at latitude L = 45°. Then we have K = (2 pi/86164) cos L = 0.00010313 and K² = 1.0635e-8. We are assuming P = 8,000, and we know GM = 398,600. So 2GMP = 2 x 8,000 x 398,600 = 6.3776e9, and we have

(1.0635e-8) A³ (A + 8,000) = 6.3776e9

so

A³ (A + 8,000) = 5.9968e17

with the numerical solution that A = 26,020 km to 4 significant digits. Taking the Earth's radius at your latitude as 6,370 km, the answer is that you would have to climb 19,650 km or say 12,210 miles in order to jump off and reach a stable orbit with the perigee mentioned above.

If your backyard is on the equator, you're in a much better position. In that case K² is larger by a factor (cos 0 / cos 45°)², which conveniently is exactly 2, which makes A³ (A + 8,000) smaller by the same factor, i.e.

A³ (A + 8,000) = 2.9985e17

This has the numerical solution A = 21,630 km. If your ladder is at the equator, you must climb a mere 15,250 km or 9,475 miles to jump into a stable orbit. And if you wanted to enter a geostationary orbit (not a bad idea if you ever intend to come back down using the ladder!), then on the equator it would be possible by climbing to the height mentioned above. Anywhere else, of course, it would not be.

--Anonymous, edited 04:49 UTC, November 9, 2007.

The effect of stars on Earth

What if a genie were to withdraw all of the stars in the universe except the sun, and the photons in transit to Earth were taken away as well. Would there be a gravitational effect? Would there be a climate change on Earth? Essentially, do the stars in the night sky play any describable role in Earth's affairs? —Preceding unsigned comment added by 150.167.179.111 (talk) 17:00, 8 November 2007 (UTC)

Well, stars provide a useful amount of light on a clear night (see night vision), but I think there's no other routinely discernable effect. The opinions of astrologers will differ, of course.

Note: It is thought that a sufficiently close supernova would emit enough gamma radiation to toast us all, but I think we all hope that won't occur any time soon, so I'm excluding that as a current effect.

Atlant 17:11, 8 November 2007 (UTC)

The stars are all far enough away that gravity is not an issue; starlight doesn't make up an appreciable amount of radiation reaching Earth so it shouldn't have any effect on the temperature, climate, etc. My bet would be "no". The stars don't play any real physical role in Earth's affairs. --24.147.86.187 18:57, 8 November 2007 (UTC)

For that matter, said genie could remove everything but Earth/Moon/Sun and we'd see no appreciable difference apart from the view in the nighttime sky. — Lomn 19:10, 8 November 2007 (UTC)

In terms of climate, the effect of the loss of every single star is essentially nil over any short or medium time scale. (Over an extremely long period of time – hundreds of millions of years – there's the risk Atlant notes of a nearby supernova explosion.) This web page talks about using single stars as light sources of known, carefully-measured intensity for evaluating the sensitivity of digital camera sensors. Interestingly, it also provides the relative illumination provided by starlight (0.001 lumens per square meter) compared to full daylight (10 .000 lumens per square meter). Making the reasonable assumption that most of the energy we receive from starlight will be at visible and near-visible wavelengths, distant stars contribute less than a millionth of the incoming radiation to Earth.

As for gravity, the effect is again negligible unless a massive star passes extremely close to the Earth-Sun system. (This would be a very rare event.) Since gravitational force follows an inverse square relationship, a star the size of the Sun only one light year away will pull on the Earth lss than one-billionth as strongly as the Sun does. TenOfAllTrades(talk) 19:52, 8 November 2007 (UTC)

On the other hand, the effect could be catastrophic. See Ice_age#Causes_of_ice_ages. While I don't believe this theory, just remember that we are in some kind of orbit around a galactic center, and therefore there is a very real gravitational effect on the Earth and Solar System. The planets and outer solar system all have enormous influence regarding the slinging of comets and asteroids into Earth's path, and there are clear measurable gravitational effects from Venus, Mars, and Jupiter. The moral of the story is that in a chaotic system like climate and ecology, you cannot just ignore the small variables. SamuelRiv 20:28, 8 November 2007 (UTC)

On the one hand, the physical effects on the planet are described above. On the other hand, there is the potential effects on society and humanity. Consider the espers' trick on Ben Reich in The Demolished Man, multiplied by six billion, or the end of "Nightfall" in reverse... the sudden disappearance of every single star in the universe would be quite traumatic. The most calm would be rightly troubled, and the least calm would revert to base fears, thoughts of religiously inspired (or even very real) armageddon. When people panic on large scales, Bad Things Happen. If everyone in the world is exposed to the same instantaneous trauma (and even something as simple as the stars disappearing can be quite effecting, I'd imagine), its a safe bet that human society as a whole would have a fairly hard time coming through and recovering from such a scenario. --Jeffrey O. Gustafson - Shazaam! - <*> 10:54, 12 November 2007 (UTC)

growing crystals of copper sulfate

how would you make a hot, concentrated solution of copper sulfate? —Preceding unsigned comment added by 86.42.210.0 (talk) 17:24, 8 November 2007 (UTC)

You would boil some water (perhaps in a kettle), pour it in a heat resistant glass or ceramic container, then add copper sulphate crystals and stir. Do not use aluminium or steel containers as copper will plate on to their surfaces. Then you decant the solution, leaving any undissolved stuff behind. Commercial copper sulphate probably has ferrous sulphate as well, so it may not be pure. As the solution cools you will get a growth of crystals. If you can hang a little crystal from a thread, you can make it grow into a big crystal. Other experiments you can do with copper sulfate solution are: add ammonia to get a dark blue solution which can dissolve cotton, add biuret to get a different dark blue solution, add a base like sodium bicarbonate to make a precipitate. Graeme Bartlett 20:14, 8 November 2007 (UTC)

Viruses

Virus is a DNA With a Protein Coat Protecting It Can a virus be destroyed if the protective protein coat is damaged so that it cant protect DNA anymore if yes then can an enzyme be used as protease to digest the protein coat thus destroying the virus ????? —Preceding unsigned comment added by 212.71.37.97 (talk) 18:04, 8 November 2007 (UTC)

Proteases generally act, well, in a general way. They either consume a protein at one of its ends, or they cleave proteins at specific amino acids. So as you can see, a protease based antiviral measure would cause quite a bit of collateral damage if used to "carpet bomb" infected tissue. It could destroy or inactivate the virus; however, some viruses are even evolved with this in mind, and cleavage of viral proteins upon entering the cell can actually activate the virus (I can't for the life of me remember what article this is in, but it came up in a previous ref desk question I can't find in the archives). Far easier to target them with antibodies. Someguy1221 19:39, 8 November 2007 (UTC)

Something like http://dx.doi.org/630030? DMacks 21:19, 8 November 2007 (UTC)

Also, your definition of "virus" is not quite right. There are many RNA viruses. And the RNA of many of those viruses can infect cells as "naked RNA"; no protein coat is required for the virus to infect cells and produce new virions. - Nunh-huh 21:18, 8 November 2007 (UTC)

ecosystem

can you show me a picture of an ecosystem (example) that a 4th grader could use to help them do a project? —Preceding unsigned comment added by 72.18.102.36 (talk) 20:16, 8 November 2007 (UTC)

I like the images and text here. But there were other suitable examples when I did a google image search. Man It's So Loud In Here 21:08, 8 November 2007 (UTC)

nuclear energy: a given

Let's face it: we are running out of oil. The federal "government" doesn't have a plan for the event known to the public (or is the coal industry now going to move in for what it's worth?). We are in a bad spot so we quickly fall back to our former nuclear technology, which could be a rescue except for the problem of "spent" nuclear fuel. So has there been any design for a facility that can "speed up the procees of nuclear decay" of a spent fuel on-site? Can a half-life be made into a quarter-life? There's energy there. LShecut2nd 23:29, 8 November 2007 (UTC)

Radioactive decay is a quantum process and as far as I know there's no way to affect it one way or another. That being said, there are plenty of other ways that one can imagine dealing with the waste problem. Unfortunately the stakes are quite high and the need for government intervention quite high as well so as a result it is a rather toxic bureacratic issue, so to speak, and progress has been pretty slow and problematic. --24.147.86.187 00:21, 9 November 2007 (UTC)

Breeder reactors are one technology that affects the quality and quantity of waste by transmuting some of the waste into other substances. The drawback is that this technology produces plutonium which is much easier to use as the core of a nuclear bomb than ordinary reactor materials. Dragons flight 01:39, 9 November 2007 (UTC)

It is a fundamental mistake to say that we are running out of oil. If (hypothetically) we were to continue consuming it at the rate we do now then we would indeed run out in 40 to 150 years (depending on the economics of pulling oil from sands and shales as the price inevitably rises). However, if we burn oil at this rate for even 20 more years, the planet will die. So given that we don't intend to kill the planet - we WILL cut our consumption. So - the problem remains - somehow we have to stop using oil. Certainly there are alternatives - nuclear isn't wonderful - but the difficulties of safely storing nuclear waste is a lot more tenable than the the problems of collecting and storing millions of tons of CO2 gas. Nuclear waste will trash the environment wherever we put it - but it's a lot better than trashing the entire planet. So let's pick a place (right in the middle of a desert someplace might be good) and dump all of the stuff there. Sure, the consequences will be nasty - but a heck of a lot less than melting ice caps, rising sea levels, increasing human misery - annihilation of some terrifying percentage of the species of life.

But you can't speed up the rate that the low level waste decays. Sure, it contains energy - but at a level that can't be economically recovered. There really isn't much you can do but let it decay. The plan ought to be to use nuclear as an emergency stop-gap. We URGENTLY need to get away from fossil fuels - and the efforts with wind, solar, wave, etc really aren't cutting it - and the one renewable resource that did anything (hydroelectric) has proven to be a problem, the dams silt up and the downstream environment suffers...argh! So we need to build a bunch of nuclear power plants - shutting down the coal, oil and gas plants as we do so. Then research - LOTS of SERIOUS research. Whatever happened to huge orbiting solar power plants with microwave downlinks? Why aren't there VAST numbers of windmills everywhere? Fusion power - perpetually "25 years away" from getting something working...we need a 'Manhatten Project' for fusion. For vehicles, we have other problems - cheap electricity could solve it - but I think ethanol may be the more likely answer.

SteveBaker 02:42, 9 November 2007 (UTC)

It is quite easy to speed up nuclear decay. First, you need to chemically separate the waste into elemental components, since they must be treated differently. Then, use a neutron source to bombard the correct set of your elements. You can get the neutrons from a fusion reactor. The process can be engineered as a net power source. None of this can be done today: the science is there, but the engineering is not. This is however a way that our grandchildren can eliminate the low-level nuclear waste that we must generate to avoid killing ourselves with oil. -Arch dude 03:04, 9 November 2007 (UTC)

Well, have a look on Fusion power and ITER. Thermonuclear reactors are the next-generation-nuclear-device which would produce far less waste while consuming heavy water (D2O, more precisely, heavy isotopes of hydrogen: deuterium and tritium), i.e. they will be able to provide Humankind with cheap clean energy. —Preceding unsigned comment added by 62.63.76.14 (talk) 09:51, 9 November 2007 (UTC)

Is fusion energy really all that clean? The fusion reactor itself becomes highly radioactive. "...most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. By 300 years the material would have the same radioactivity as coal ash..." If fusion energy became viable on a world scale to power everything, how bad of a nuclear waste problem would we have? Sappysap 14:24, 9 November 2007 (UTC)

Probably very little; there isn't anything important under the Sahara and Gobi deserts, or the Great Basin of Nevada. These would hold massive quantities of waste. —Preceding unsigned comment added by 98.196.46.72 (talk) 16:12, 11 November 2007 (UTC)

Also see Integral Fast Reactor, and this Q&A here. Too bad the project was killed, eh? grendel|khan 15:36, 9 November 2007 (UTC)

Reichsbrücke

The Reichsbrücke article does not state why the bridge collapsed and was anybody found guilty. Does anybody know any details concerning that collapse? Mieciu K 23:58, 8 November 2007 (UTC)

Following the third link in the References section, I find this paragraph:

Ursachen. Nachdem zunächst Gratz seinen Rücktritt angeboten hatte, übernahm der Wiener SP-Planungsstadtrat Fritz Hofmann die politische Verantwortung für den Einsturz und schied wenige Tage nach der Katastrophe aus dem Amt. Eine Expertenkommission gab kurz darauf bekannt, dass der linke Pfeiler der nach Ende des Zweiten Weltkrieges sanierten Brücke zum Teil mit Sand und "unverdichtetem Beton" gefüllt gewesen war. Durch das schlechte Material sei Wasser eingedrungen, was schließlich zu dem Einsturz führte.

Combining pieces from two machine translations of this (Google Language Tools and Babelfish) and putting the word order into something more like English myself, I figure that this says:

Causes. After Gratz [the mayor] initially offered his resignation, the Viennese FR planning town councillor Fritz Hofmann took political responsibility for the collapse and resigned from office a few days after the disaster. An expert commission shortly afterwards announced that the left column of tbe bridge, rehabilitated after the end of the Second World War, had been partially filled with sand and "uncompressed concrete". Water penetrated by the bad material, which ultimately led to the collapse.

--Anonymous, 03:29 UTC, November 9, 2007.

November 9

Robinson projection

I'm beating my head against the wall. I want to come up with a simple script that will convert latitude and longitude coordinates to x,y coordinates on a given map in a Robinson projection of a given width with a given central meridian. Ideally this would be done in Actionscript but if I had it in any sort of code or pseudocode that would be fine (which is why I am asking here and not the computing desk—it is not a computational difficulty, it is a conceptual one. Once I have an idea of what I should be doing conceptually it will be trivial to code it).

There are a few map projection projects out there but they are all extremely complicated since they are designed for exporting ALL projections; I _just_ want Robinson. I've read the article and I grok that it's about a lookup table but I still have no idea how I'm supposed to convert that table into x,y coordinates with a given map.

Can anybody help? I just want instructions on the level of "take your number from column one, multiply it by something in column two, then do something else, do something with the central meridian and the width, and presto-chango you have x and y coordinates." I'm having trouble figuring out how to use the table. --140.247.10.141 00:18, 9 November 2007 (UTC)

The general method will be to get a formula that maps the points from one projection to the other. THen you invert the formula so that it maps the points in the reverse direction. Then scan all the points on your new map, say from top left to right and then going down in a raster pattern, use the formula to get a new coordinate to look up the original map. If the coordinates are on the map copy the pixel. If its off the map stick in a "missing data " colour - perhaps white or blue. Graeme Bartlett 01:19, 9 November 2007 (UTC)

Graeme, A Robinson projection is not a formula driven mapping.

Matlab code snippet

robval = [
00 1.0000 0.0000 
05 0.9986 0.0620 
10 0.9954 0.1240 
15 0.9900 0.1860 
20 0.9822 0.2480 
25 0.9730 0.3100 
30 0.9600 0.3720 
35 0.9427 0.4340 
40 0.9216 0.4958 
45 0.8962 0.5571 
50 0.8679 0.6176 
55 0.8350 0.6769 
60 0.7986 0.7346 
65 0.7597 0.7903 
70 0.7186 0.8435 
75 0.6732 0.8936 
80 0.6213 0.9394 
85 0.5722 0.9761 
90 0.5322 1.0000 
];

robval(:,3) = robval(:,3) * 0.5072;
robval = [robval(end:-1:2,:);robval(1:end,:)];
robval(1:90/5,[1,3]) = -robval(1:90/5,[1,3]);

rvals2 = interp1(robval(:,1),robval(:,2),latitude,'cubic');
rvals3 = interp1(robval(:,1),robval(:,3),latitude,'cubic');
y = -rvals3;
x = rvals2/2.*longitude/180*2;

The above is taken from a Matlab program I wrote to generate a Robinson projection. Dragons flight 01:35, 9 November 2007 (UTC)

does it use cubic interpolation? the article does not say what kind of interpolation is used. Graeme Bartlett 01:44, 9 November 2007 (UTC)

My quick search didn't turn up specifics on the kind of interpolation (other than the phrase "simple interpolation method"), but this page shows an example Robinson map with a caption saying "...calculated with 3rd degree polynomial interpolation", for what it is worth. Pfly 06:29, 9 November 2007 (UTC)

That looks like it is in the right ballpark. Here I admit to not being able to follow MatLab's syntax with dealing with Arrays. Could someone convert it into something a little more standard, or just pseudocode? I feel like I'm on the cusp of having it but researching how MatLab deals with Arrays is something I'm not very excited about... --140.247.11.32 16:09, 9 November 2007 (UTC)

Muteness

If you're born mute due to brain damage rather than throat/vocal cord damage, as an infant, do you still cry? Assuming you can hear, what happens when you learn to understand language? Do you merely stop crying but not be able to communicate until someone teaches you sign language? In fact, is it even possible to be mute but not deaf as a result of brain damage? Or would it have to be throat/mouth damage? Kuronue | Talk 02:06, 9 November 2007 (UTC)

I'm not sure about the physiology of crying (there is no article on crying here, unfortunately), but it seems to be associated with contraction of the diaphragm, and should occur with or without vocal chords or vocalization control. Children can hear their own voices, and it's an extremely important part of their personal language development, so a mute child will probably have to learn some sort of gesture or sign language to compensate, and if one isn't taught, it will probably imitate or invent such a language from what it perceives from others (gestures, etc). Unfortunately the pages here for muteness and aphonia are also lacking. Brain damage can cause muteness if the damage is significant enough to somewhere such as Broca's area, which would affect speech production, though it would damage a lot of other linguistic abilities as well such that someone with such damage may not be able to perform sign language. A much more mild damage would be from, say, damaging one of the facial nerves that control the mouth and tongue, which would easily destroy comprehensible speech. Finally, of course, a laryngectomy of the sort that Steven Hawking went through would destroy vocalization completely. SamuelRiv 06:10, 9 November 2007 (UTC)

No other responses, huh? Why is it that there's so little information? I meant mostly the verbal part of crying - if the vocal cords function but the bit of the speech center that organizes sound into speech does not, I'd think the infant would scream but then... would the child merely become silent around 2-3 years of age when others learn to speak? Also, good point, if it's brain damage to the Broca's Area or similar, he might not be able to learn sign language... *ponders* Maybe I'm making this too hard for myself. The character I'm writing is a young boy of about 6 who cannot speak, but I want him to be able to respond to the telepathy, and he's not visibly deformed - I was going to go for some sort of umbilical-cord oxygen-deprivation at birth scenario. I oughta just have his vocal cords themselves be malformed due to mutated genes or something... Kuronue | Talk 17:06, 13 November 2007 (UTC)

asbestos -microencapsulization healing?

Once fibers get in the lung, they can't be removed., sometimes leading to cancer. When re-modeling a house, asbestos that can't be removed is encapsulated with an impenetrable material. Why can't micro-encapsulization, biological or chemical, be used likewise to neutralize fibers in situ? Wiki articles on microen. and on 'self-healing' were good. Comments? —Preceding unsigned comment added by 76.182.3.188 (talk) 02:11, 9 November 2007 (UTC)

Well, microencapsulation wouldn't remove the actual foreign particle from the lung, which I believe (not my field at all) is the primary cause of the cancer in the first place. See carcinogen. Aside from that, encapsulating the fibres should be feasible with molecules attracted the long mineral, but I'm not sure of any such engineering out there for individual strands. SamuelRiv 06:15, 9 November 2007 (UTC)

Exactly. One of the things that asbestos does (Asbestosis) happens because the particles are essentially impenetrable. The lung detects the presence of the foreign particle, triggering an immune response. Essentially it releases some localized acid to try to dissolve the particle, which does not work on the asbestos particle, but over time does start to dissolve lung tissue. Coating the asbestos in some other impenetrable shell would likely result in the same thing, unless you could use something invisible to the immune system and non-irritating to the tissues to avoid that response. Not medical advice! Arakunem^Talk 15:53, 9 November 2007 (UTC)

Time

• Will time "be faster" if an event caused the Earth to rotate faster? (and vice versa)
• Does the moon going farther out from the Earth affect the rotation of the Earth?
• Also, could this be happening now?

Time recently has been going by so freaking fast. I worship seconds now. 67.35.94.120 02:27, 9 November 2007 (UTC)

No, No, Yes. Time wouldn't change if the earth rotated faster - the length of a day would get shorter - but the definition of a second (and therefore a minute and an hour) is defined by the rate of some atomic event or other...something that will never change. The orbit of the moon doesn't significantly affect the rotation of the earth - although doubtless there is some small effect or other. The moon is most definitely gradually moving away from the earth - but not at a rate that you could possibly notice even over many human generations. Sadly, your subjective rate of time flow is something we can't do much about - but it is entirely subjective. SteveBaker 02:39, 9 November 2007 (UTC)

Actually tidal drag caused by the moon is the primary effect slowing the rotation of the Earth and is directly linked to the growth in the moon's orbit. It is still a very small effect though. Dragons flight 03:01, 9 November 2007 (UTC)

(ec) Angular momentum is transferring from the spinning earth to the moon's revolution about the earth by a mechanism involving the tides. As the moon moves away, the earth is slowing down. Yes this is happening now. This causes the day to get longer, but the effect is small. We now must add about one second per year to keep the clocks and synchronized with the earth's rotation: see leap second. -Arch dude 02:41, 9 November 2007 (UTC)

Actually, when I read the question I assumed anon was referring to special relativity effects of reduction in relative velocity to the perception of time. The centripetal acceleration that we feel makes the calculation non-trivial, but in general our time would be "slower" than that of an observer stationary relative to our rotation. SamuelRiv 03:38, 9 November 2007 (UTC)

(By a negligable amount...yes) The point is that while there are such effects, they are all quite utterly negligable compared to human timescales. Our OP is claiming that time is going by faster than it used to within his/her lifetime...that's simple not true to any measurable degree no matter what complicated science you try to throw at it. The effect of the moon, the effect of relativity - these are all UTTERLY negligable - and it is wrong to suggest otherwise just because we can. The clear answer to the OP's question is "No". SteveBaker 14:11, 9 November 2007 (UTC)

absorption refrigerator

Look at this http://www.nh3tech.org/abs.html

Since absorption refrigerator uses heat to chill things down and since CPU generates a hot of heat. Why isn't absorption refrigerator uses the CPU heat to cool down hot CPUs? 202.168.50.40 04:15, 9 November 2007 (UTC)

Expense, complexity, and environmental hazards. Basically the first two are the same reason computers don't come standard with liquid cooling. Air cooling is by far the simplest, cheapest, and safest answer for most processors. SamuelRiv 04:25, 9 November 2007 (UTC)

Another reason is that you can't use the heat from the thing you're trying to cool as the energy source for the system. If you cool the CPU, it won't be hot, so it won't be able to boil off the ammonia, so the CPU will heat up until you cool it again, at which point it won't be hot...you get the idea. And you don't want the CPU to be hot enough to power the system in the first place. I remember learning about the ammonia system when I was tutoring my landlord's kid. It's a fascinating machine. It's one of those inventions that is NOT obvious once someone's done it the way the cat door is. --Milkbreath 14:16, 9 November 2007 (UTC)

paleontology & neuroscience

If the brain of a dinosaur or other prehistoric organism were discovered, perfectly preserved so as to be in the same state as moments after its death, what facts about its behaviour, intelligence, memory capacity, etc. would neuroscientists & paleontologist be able to confidently infer from the brain & nothing else.

Hypothetically-speaking; please disregard whether such a brain could possibly be found in reality. 3170s228 04:42, 9 November 2007 (UTC)

From the perspective of neuroanatomy, an awful lot. From a cognitive perspective, next to nothing. Animal brains (which I know nothing about) are a lot different from human brains, but in general we could find out most innervation and structure of the brain, which would tell us quite a bit about a variety of processing abilities. Intelligence is usually measured in terms of cerebrum size, so we'd have an estimate of that. We may be able to infer some things about memory if limbic structures are present, including the apparent structure of long-term memory and perhaps even its synaptic plasticity. With present understanding, however, we could infer next to nothing about behavior - I don't see any real viable correlation of brain structure to behavior in a class of animals like reptiles. SamuelRiv 05:33, 9 November 2007 (UTC)

Animals tend to have similar brain parts. Knowing the existence and relative sizes of different parts of the brain can tell you a lot. They hardly need a perfectly preserved brain. The cavity in a fossilised skill would do. I remember seeing something where they showed that the brain of some kind of dinosaur was similar to that of an alligator and that it probably behaved like one. — Daniel 01:29, 10 November 2007 (UTC)

How would one find out about the kind of society of prehistoric humans?

How would someone find out about the kind of society that existed among prehistoric humans 50,000 years ago? I am not asking what the answer actually is but rather how you would find the information. I do not mean by like research but how would like scientists find out this information. Any help would be appreciated. —Preceding unsigned comment added by 69.181.131.67 (talk) 05:16, 9 November 2007 (UTC)

Great question! As you might guess, information about the social structure 50,000 years ago will be fairly limited. What kind of inference you make will be based on whatever physical evidence is preserved. By examining what kind of tools they had, and what wear was associated with them, along with bones or other trace detritus, it may be possible to guess at what they ate (some other techniques, such as Isotope analysis also can be telling in this regard). Sometimes human skeletal remains can give clues about how the person lived, although this is tricky at long ages. Occasionally a glimpse of the "soft culture" is given; One (Neanderthal) skeleton recovered from the Shanidar site indicates injury and healing. A reasonable guess, since he would have been unable to fend for himself, is that he was cared for by his companions. Was there a specific question which prompted the interest? --TeaDrinker 05:37, 9 November 2007 (UTC)

Note bones also tell about religious practices and superstitions. Garbage (discarded bones of killed animals tell what they hunted and how) and housing are other important finds. Then one can look at probable migration patterns or recorded history to see where that society went: if a descendant society still exists, one could learn a lot from examining them and their own perception of history. Linguistic history of any kind could almost certainly not be traced that far back, unfortunately. SamuelRiv 05:41, 9 November 2007 (UTC)

An overly broad and probably not very helpful answer: Look at the archaeological record and, using everything we know in modern science (particularly medicine) and current cultures with deep roots, make some "educated" guesses. --Bennybp 07:38, 9 November 2007 (UTC)

• A while back they did a reconstruction in Germany. Build a prehistoric village and have people live there in the way the prehistoric people did. They're interactions changed significantly from what they were used to in modern life. You can Google on SWR and "Das Steinzeit Experiment". - 131.211.175.100 12:26, 9 November 2007 (UTC)

First Solar

According to this

According to Deutsche Bank analyst Steve O’Rourke, the company’s results came in well ahead of expectations as its German production facility ramped ahead of schedule, and incremental improvements in efficiency, production throughput, and currency exchange rates drove panel cost per watt to a new low of $1.19

Does that mean I can buy a 65 watt solar panel from First Solar for only $78 dollars???

5kW worth of Solar Panels for only $6000 + installation cost?

220.237.184.66 06:14, 9 November 2007 (UTC)

Well, perhaps - but maybe they don't make them in 65W sizes. You are assuming that this is the cost of a complete unit that you can bolt onto the roof of your house (or whatever) and use - that may not be the case. I suspect they are talking about the raw silicon wafers - it may cost considerably more to assemble them into weatherproof units, add controller electronics, etc. Is that the retail cost or the wholesale cost - if you're going through a middle-man, it could be more. In short, no, it doesn't necessarily mean that...although it might. SteveBaker 14:03, 9 November 2007 (UTC)

gryroscopes

Can two gyroscopes spinning in opposite directions counteract each other? —Preceding unsigned comment added by 204.251.179.61 (talk) 07:05, 9 November 2007 (UTC)

Sure. Why not? It all depends on what you mean by "counteract". -- kainaw™ 13:17, 9 November 2007 (UTC)

From my interpretation of the question, it seems you're asking if two gyroscopes in the same system but spinning on different axes and otherwise not interacting counteract, and the answer is yes and no. No in the sense that they both will resist changes in their absolute spin axis to conserve angular momentum, so they will still keep an object on a stable trajectory. However, a single gyroscope can have its system rotated about the gyroscope's axis without problem, so you need a second gyroscope in a different direction to restrict all rotation. In this way, they do have an interaction effect. SamuelRiv 13:56, 9 November 2007 (UTC)

If they are bolted together then as you try to turn them, each gyro will exert a force onto their common framework - the resultant force will apply. It's no different than if you bolted two cars together and tried to steer them in opposite directions. Gyroscopes (like magnets) have taken on a mystery that they don't truly deserve. SteveBaker 13:59, 9 November 2007 (UTC)

Man, magnets are really, really awesome, and do deserve every bit of mystery that they're given! Invisible forces! Immense power in tiny pieces of metal! Wow! I'm still amazed by magnets, they're the closest thing to magic that I interact with on a daily basis! --24.147.86.187 21:25, 9 November 2007 (UTC)

I dunno - gyroscopes are pretty weird too. Take the front wheel off your bicycle, hold it by the axles and sit in a swivel chair - now have someone spin the wheel up as fast as they can get it to go - then tilt the wheel back and forth...tell me that ain't freaky on the scale that magnets are. But you're wrong about the magnets having "immense power" - they don't store any energy in the form of some kind of "magnetic power" in the way that (say) a battery stores electrical energy. SteveBaker 21:52, 9 November 2007 (UTC)

All I really mean by "immense power" is "electromagnetic forces are so much more powerful (on small scales) than gravitational ones, which is awesome to think about. A magnet can totally kick earth's ass when it comes to attracting a piece of metal." --24.147.86.187 06:04, 14 November 2007 (UTC)

As a related question, if you've got a sealed box containing two counter-rotating coaxial flywheels, is there any measurement you can do to tell if the flywheels are rotating or not? How about if the axises of rotation are parallel but not co-linear? --Carnildo 21:43, 9 November 2007 (UTC)

So it won't matter if the axes of rotation are not collinear at all. You can translate your whole spinning system arbitrarily and nothing will change. The angular momentum vectors of the two flywheels won't cancel - both will resist angular momentum changes of their respective systems. So if you turn the box, you will feel twice as much restorative force from the conservation of ang mom as if you only had one flywheel, whether or not they're spinning in the same direction. SamuelRiv 23:38, 9 November 2007 (UTC)

This problem is a little more subtle than first meets the eye. The behavior of a gyroscope is normally just governed by the conservation of angular momentum. However, if you have two identical rotors with collinear axes in one rigid frame, rotating with equal speeds in opposite directions, the angular momentum of the two rotors cancel out, and the net angular momentum of the system is zero. So it would appear at first glance that you should be able to rotate the system as easily as any other object with the same moment of inertia, since there is no net angular momentum to be conserved. If you apply a torque to the system, the precessions due to the two rotors are in opposite directions, so there is no net precession.

However, there is a complication. If you apply a torque to the system, the tiny bit of precession that each rotor is able to perform will cause stress on the frame – compressive stress on one side of the frame, and tensile stress on the other side of the frame. The resulting strain in the frame will cause the frame to act like a spring, and resist the rotation you’re trying to apply to the system. If you remove the torque from the system, the frame will spring back to its original position.

In short, the answer to the original question is "no", and the answer to Carnildo’s question is "yes."

In the real world, there would of course also be other complications such as friction between the rotor and the frame, a finite yield strength of the frame, etc., that I’m ignoring in the treatment above. MrRedact 11:10, 12 November 2007 (UTC)

LEL and UEL of gases.

I looked at a table on your website which states the LEL and the UEL of various gases. How do I know that the information seen on your website is correct? Is this ever checked or is this just something that someone put together? I'm keen to use your website but only if the information has been verified and is correct. Thank you. Mr Sangster. —Preceding unsigned comment added by Andy Sangster (talk • contribs) 10:38, 9 November 2007 (UTC)

If you're referring to Explosive limit, then you should check the references at the bottom of the page. All information on Wikipedia should be properly sourced, so you can go to the sources if you want to be sure. -- JSBillings 13:13, 9 November 2007 (UTC)

To be honest - there are no guarantees. Whilst Wikipedia editors are supposed to provide references for all of the facts they list, this is far from typically the case - and even if there are references, you can't know for sure that the author of the article typed them in correctly from those references. Worse still, some annoying little kid could have come along and messed up all the numbers for a joke. That is actually very rarely the case - but if you want absolute guarantees - there aren't any. In the case of this article, they have not indicated specifically where that particular information came from - but merely listed the two references were used in writing the article. In order to check that this particular set of information is true, one would have to look into the references and check to see that the information in the article actually agrees with them. In a better referenced article (such as the ones I wrote for the Mini and Mini Moke cars), you'll see little blue tags that look like this: ^[25] which you can click on to take you to the exact reference where that particular fact came from. However, as I said, sadly not all articles are referenced to that standard. As a practical matter, most scientific Wikipedia articles such as Explosive limit are reliable. I wouldn't use the information (without checking the references first) if someones life depended on it - but for more casual uses it's convenient. Wikipedia has been shown in several surveys to be more accurate than printed encyclopedias such as the Britannica. So I guess you can trust Wikipedia to the same degree that you'd trust any general encyclopedia. SteveBaker 13:53, 9 November 2007 (UTC)

Wikipedia is inherently no more or less reliable than any other encyclopedia. Per Wikipedia's Risk disclaimer and General disclaimer, you should place the same trust in this material as you should in material from any general encyclopedia: none at all. If you are going to be handling flammable gases, contact the manufacturer for up-to-date information (UEL and LEL are often listed in the MSDS that ships with products), or perform your own tests. Depending on your location, there are any number of independent testing labs that can measure vapour pressures and explosive limits, as well. TenOfAllTrades(talk) 14:23, 9 November 2007 (UTC)

Of course Wikipedia is less reliable than a real encyclopedia. It has advantages in other areas, of course, but professional editing counts for something. --Anon, 02:00 UTC, November 9, 2007.

Surprisingly, (actually, AMAZINGLY SURPRISINGLY) that's not true. Wikipedia is actually more reliable than almost any other encyclopedia - the venerable Encyclopedia Britannica is normally considered the 'gold standard' of encyclopedias - and Wikipedia is about on a par with it in terms of accuracy and miles ahead on breadth of coverage. Wikipedia is by any measure most certainly a 'real' encyclopedia - whatever that means. As to whether "professional editing" matters - I'd say that results say not. Here are some often-quoted facts:

• A 12-year-old kid [15] found five errors in Britannica after just a couple of days of checking. His only recourse was to write to the editor, and the errors may be corrected in print in a few years.
• Nature magazine did an extensive study of science articles by experts in those fields and found: "Our staff compiled lists of factual errors, omissions and misleading statements that the reviewers pointed to (we had 42 usable responses) and tallied up the total number for each encyclopaedia: 123 for Britannica, 162 for Wikipedia." - of course all 162 of the Wikipedia errors were fixed within a few days of the list being made public. You still can't buy a copy of Britannica with the 123 errors fixed up.
• Wikipedia:Errors in the Encyclopædia Britannica that have been corrected in Wikipedia
• Wikipedia:External peer review

So don't write off Wikipedia as "obviously" less reliable - there have now been half a dozen proper academic studies - and they all sow that Wikipedia and Britannica are about equal - and both are miles ahead of any other general-purpose encyclopedias out there.

SteveBaker 18:56, 10 November 2007 (UTC)

It's safe to say Britannica and the other "professionally edited" encyclopedias don't have quite the same vandalism problem, though... —Steve Summit (talk) 20:39, 10 November 2007 (UTC)

Also, if only to play devil's advocate, those "often-quoted facts" might seem to an impartial outside observer to be a wee bit biased and one-sided. The first doesn't say anything about Wikipedia's error rate; the second says that Wikipedia has (or had) more errors than Britannica. The third and fourth come from Wikipedia itself, so despite Wikipedia's vaunted principle of NPOV, they can't be assumed to be entirely balanced.

(I bet I could find five errors in Wikipedia after only a couple of minutes of checking -- what does that say?) —Steve Summit (talk) 20:46, 10 November 2007 (UTC)

You aren't a 12 year-old. SteveBaker 23:29, 10 November 2007 (UTC)

To answer the middle part of the question: yes, the website was "just put together by someone" -- quite a few different someones, in fact -- and it has also been checked, if not 100% systematically, by other someones.

Now, for any given fact, was it entered correctly by the someone who entered it, and has it ever been checked by someone else? Maybe. Maybe even probably. But definitely not definitely. —Steve Summit (talk) 23:18, 9 November 2007 (UTC)

methylphenidate Q.

http://en.wikipedia.org/wiki/Ritalin#Known_or_suspected_risks_to_health

The R.A. El-Zein study says it will cause chromosomal abberations. I'm no biologist and dont really understand these things, but does this just refer to normal body cells and the only problem is that it could possibly cause cancer, or will it mutate gamete cells as well and these mutations passed on to offspring... thank you Rocktruly21 14:43, 9 November 2007 (UTC)

That study only tested lymphocytes for chromosomal abberations, so this would be called "need for further testing." It should be noted, however, that this study's results were not reproduced to any extent by a much larger but otherwise identical study, as mentioned in the same section you linked to. Someguy1221 18:23, 9 November 2007 (UTC)

SILVER RINGS

hi again.. please choose one of those 4 choices as an answer. question= SILVER RINGS ARE... choices= a) homogenous mixture. b) compound c) element please justify to me your answer because i have a test coming up in this and i REALLLY need to know since my book doesnt provide an answer. thank you alot, jimmy —Preceding unsigned comment added by 212.71.37.73 (talk) 20:00, 9 November 2007 (UTC)

Do you mean rings made of silver? If so, then, if they were not rings what would they be? —Tamfang 20:09, 9 November 2007 (UTC)

Jewelry is not generally made from pure elements, even though they are named to make you think they are; pure gold or silver just don't have the necessary strength. RIngs are made of alloys, which are homogenous mixtures. When you're talking about jewelry, "gold" = gold + copper or nickel or palladium; the actual gold content will be specified in terms of karats, with 24 karat being pure gold. "Silver" = silver + copper or germanium, zinc, platinum, silicon or boron.; silver content is specified in terms of percentage. (a) is the answer you're looking for. - Nunh-huh 20:26, 9 November 2007 (UTC)

Silver jewelery is most often an alloy called sterling silver. Graeme Bartlett 20:43, 9 November 2007 (UTC)

Since this is a test - I'd bet the answer is 'Element' because silver is an element. There are practical matters to do with how jewellery is often made of an alloy of silver and something else - but unless you are doing a test in jewellery-science, they won't expect you do know that. The point is that 'silver' is not like 'bronze' (which is a homogeneous mixture) or 'sugar' (which is a compound). SteveBaker 21:48, 9 November 2007 (UTC)

On the contrary, "silver" in the mouth of a jewelry dealer means "mostly silver" = silver alloy. If the answer isn't (a), demand a recount. - Nunh-huh 22:55, 9 November 2007 (UTC)

Umm, what is (d), the fourth choice? hydnjo talk 23:38, 9 November 2007 (UTC)

the scifi kitchen

If you were to cook beef in an oxygen-free atmosphere, would it turn brown? —Tamfang 20:08, 9 November 2007 (UTC)

I'm not a chemist, but the browning reaction is the Maillard reaction, in case that helps anyone. -- Coneslayer 20:17, 9 November 2007 (UTC)

Yes it would still go brown, and black if you over heated it! Think what happens when you deep fry food. There is no oxygen in the liquid hot fat, but things still go brown or black. Graeme Bartlett 20:40, 9 November 2007 (UTC)

Ever heard of "ear music" heard by hearing impaired people?

A person who worked with hearing impaired people remarked at a seminar recently that there was such a thing as what she termed "ear music," if I recall the term correctly. I haven't found it under similar terms or this, but anyway, she said that it was sounds, almost like phantom limb of the ear, that the nerve endings pick up when it's really quiet that aren't there, as if a low radio were playing in another room or something. I asked specifically if tis might be hypnagogia, and she said this was something different, it wasn't just when one was nearly asleep. Have you ever heard of it? I found it odd there was an article under phantom eye syndrome here (which i'd never heard of myself]] but not phantom ear, but she didn't call it phantom ear. (In fact, if she had, I'd have guessed from context what she meant right away.)Somebody or his brother 20:15, 9 November 2007 (UTC)

Sounds like something similar to hallucinations experienced during sensory deprivation. Information on the web on this seems scant- most seems related to various mental disorders and brain lesions, none of which relates to hearing impairment as a whole. But I'm not sure. Maybe check the references on that page, or see hallucinations in the sane. SamuelRiv 21:36, 9 November 2007 (UTC)

Like Tinnitus? SteveBaker 21:42, 9 November 2007 (UTC)

You might be interested in Oliver Sacks newest book, Musicophilia: Tales of Music and the Brain, which devotes a whole chapter to this topic. It is apparently a lot more common than once thought, especially among the hearing impaired. Sacks calls it musical or aural "hallucination", while noting that some people object to the word "hallucination". Pfly 09:02, 10 November 2007 (UTC)

(later addition) I skimmed the chapter this morning for a bit more specificity. It's chapter 6, titled "Musical Hallucinations". Some of the things Sacks says about it -- musical hallucinations were once thought rare and perhaps associated with temporal lobe epilepsy (TLE), but in recent years it has been recognized as more common and only rarely associated with TLE. Musical hallucination is not a psychosis, not "mental illness"; rather it is "real", "physiological", and benign. Sacks stresses this point -- some people have suggested a similarity between musical hallucinations, "hearing music", and schizophrenic "hearing voices", but Sacks shows how very different the two are, both physically in the brain and in the way they are experienced. Musical hallucinations can take many forms, but common aspects include: hearing music "for real", not just "in your head"; often associated with hearing loss and "emerging" from humming and buzzing type noises (eg, humming refrigerator, tinnitus, etc); more common in the elderly but can occur at any age; when caused by something like a stroke, tends to die away with recovery, otherwise musical hallucinations tend to be "very persistent" and "chronic". Some of the striking differences mentioned: for some people the music is hear very loudly, while for others it is soft and vague. For some it can be very annoying and even intrusively disruptive, while for others it can be pleasant and easily ignored. For some the music tends to be "whole pieces" or at least whole melodies, while for others the music "fragments" into tiny bits that skippingly repeat endlessly. Most people cannot control it, but some are able to "direct" it to some degree. It is not very well understood, neurologically. There is no cure. People for whom it is life-disrupting, a doctor might be able to find ways to reduce its strength. Sacks writes that of the people he knows of who have musical hallucinations, about 80% also have some kind of hearing impairment. Also, of all people with hearing impairment, about 2% develop musical hallucinations. There's lots more in the book, and as always Sacks writes very engagingly. Pfly 19:59, 10 November 2007 (UTC)

Why is chicken, rabbit and pork meat a different color from cows, deer,elk etc?

This isn't a joke, I am truly wondering why creatures with the same basic physiology have different colored meat. Respectfully, curious —Preceding unsigned comment added by 209.237.84.150 (talk) 21:00, 9 November 2007 (UTC)

It's determined by the concentration of myoglobin in the muscle cells. See white meat and red meat. --Carnildo 21:40, 9 November 2007 (UTC)

It's not just the myoglobin but also the concentrations of mitochondria. Dark meat has more mitochondira per cell, while white meat has less. David D. (Talk) 22:23, 10 November 2007 (UTC)

As a sidenote, nitrite is used to prevent the myoglobin from decaying in cured meat. Icek 04:09, 11 November 2007 (UTC)

November 10

What is the oxidation number of carbon in methanol?

What is the oxidation number of carbon in methanol? According to the article oxidation number, I get 4 (four shared pairs of electrons, in which one of each pair belongs to carbon, results in a charge of +4 upon removal). --212.204.150.105 21:14, 7 November 2007 (UTC)

Well, the oxidation state is the charge that carbon would have if the bonds were all ionic, so you need to know, for each bond, which atom is more electronegative. Given that this could be a homework question, I'm not going to tell you the answer. Someguy1221 21:29, 7 November 2007 (UTC)

I know that the oxidation state is -2 (oxygen more electronegative and three hydrogens each less electronegative), however my question pertains to the oxidation number which according to the WP article can sometimes be different. I expect, that the oxidation number should also be two, but when I follow the instruction given in the first sentence of the WP article, I get 4, as described above. Is the article wrong or is my interpretation wrong (and if so, how)? --212.204.150.105 21:44, 7 November 2007 (UTC)

I belive that's only in reference to coordinate bonds. Oxidation numbers are usually only used for metals. Someguy1221 21:55, 7 November 2007 (UTC)

The article on oxidation state says Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed - firstly, I don't think it should say oxidation number (especially not preferentially to oxidation state) and thirdly, I read elsewhere that it should take into account the electronegativity - I think it's possible for an atom to be reduced even without a change in oxidation number, so long as the ligands of the product are less electronegative than the ligands before. Thus I think the article is at best misleading, if not wrong. --212.204.150.105 22:31, 7 November 2007 (UTC)

Slowing time

Can you make time for a particular area seem to go slower by moving away from it? That is, lets say, the TV is on, and I start moving away from it at half the speed of light, would the video on the TV appear to be going half its normal rate because it is taking longer and longer for the light to reach your eyes? What if it moved away from a given spot and I move away in the opposite direction at half the speed of light, would it appear to freeze. Of course, a TV that big that my eyes would be able to resolve it is impossible, but just asking... 208.63.180.160 00:01, 10 November 2007 (UTC)

If you moved away from the TV, in addition to something similar to the doppler effect causing it to appear in slow motion, and the actual doppler effect making everything have a lower wavelength (redshift), the relatively slower speed of light through you would make time pass slower for you. It wouldn't counter it out perfectly. Two objects moving at half the speed of light away from a certain point aren't moving the speed of light away from each other, due to the time shift. This is all special relativity stuff. If it's too advanced for you, you may prefer Introduction to special relativity or the simple english article for it. — Daniel 01:42, 10 November 2007 (UTC)

Moving either towards or away from the TV (or the TV moving towards or away from you) has the same effect, the speed of the show on the TV would change by a rate determined by the square root of 1-v²/c². If your speed is half the speed of light then you have v=0.5c - so the time distortion would be sqrt(1-0.25) or about 87% of normal speed. —Preceding unsigned comment added by SteveBaker (talk • contribs) 18:36, 10 November 2007 (UTC)

Hold on... I obviously have some sort of misunderstanding here. If the TV is moving towards me, will the photons not hit me a a higher rate than if it is moving away? If a tennis ball launcher throws a ball every second, and it is moving towards me, I will be hit by balls at a rate of greater than one per second; isn't the concept the same, so I will see the events on the TV speed up by moving towards it because the light has to travel a progressively shorter distance and thus I see "newer" light quicker than I would standing still? (I have no understanding of special relativity, and I'm not understanding the articles). 208.63.180.160 01:39, 11 November 2007 (UTC)

Your view of the way light (photons) work is incorrect - and that one single fact is the entire reason we have relativity and everything that goes with it. Unlike tennis balls, the speed of light is a constant - irrespective of the motion of the source or the viewer. This was shown most clearly by the Michelson–Morley experiment. Hence, the photons coming from the TV will hit your eyes at exactly the same speed regardless of whether you are moving closer to the TV or further away from it. You'll see 'red-shift' (if you are moving away from the TV) or 'blue-shift' if you are moving towards it - but those are changes don't alter the speed. What's happening here is MUCH weirder than the 'classical' physics view that you are taking here. When you move at half the speed of light relative to the TV, the passage of time, distances and masses all change by that 87% factor - even after you take into account the fact that you are getting closer to it so that the light waves have a shorter distance to travel. SteveBaker 02:18, 11 November 2007 (UTC)

Actually there is a speed-up effect when the TV is coming towards you at a good portion the speed of light, Steve. Imagine this isn't a TV you're looking at, but just a strobe light that pulses once a second in its own reference frame. Yes, if it's approaching you at 50% the speed of light, it only strobes once every 1.155 seconds from your perspective. BUT, since the strobe is coming towards you, the pulses will actually arrive faster than you'd expect. This isn't exactly the doppler effect, but it's very similar. I don't feel like precisely calculating which is more important, but its quite obvious if you look at extreme situations. Imagine the strobe begins transmitting from 1 light year away, but is travelling towards you at a Lorentz factor of one million. The strobe in this case is trailing so close to its own transmission that the entire 1 year lifetime of its transmission suddenly arrives at you in a 32 second spurt just a year after its light first reaches you. Now, it so happens that due to relativistic slowdown, the strobe only actually managed 32 strobes in this time, so the visual speed-up effect cancels out the relativistic slow-down effect (the former is entirely a deficiency of observation, the latter is physically happening). And so at best this can simply cancel out the appearance of relativistic slowdown, though certainly it would exacerbate such if it were traveling away from you. An effect that is not cancelled out by relativity, however, is the appearance that the strobe was traveling at a velocity equal to its Lorentz factor, in units of the speed of light. This actually has to be taken into account in observations of the plasma ejections of quasars, some of which have an "apparent velocity" greater than that of light, before this effect is accounted for. Someguy1221 02:50, 11 November 2007 (UTC)

What you are describing is exactly the Doppler effect. Its magnitude is given by the Doppler formula, the longitudinal case of which is quoted in MrRedact's reply below. -- BenRG 00:17, 12 November 2007 (UTC)

Steve made a mistake. Your (the original poster’s) intuition about the case where the TV is moving away from you is almost correct. If you’re watching a TV moving away from you at half the speed of light, it will look like the show is being shown at 0.577 times as fast as its normal rate. In the limit as your speed away from the TV approaches the speed of light, the rate at which the show looks like it’s being shown approaches 0, i.e., it approaches looking like the TV show is stuck on one frame.

If you’re watching a TV coming at you at half the speed of light, it will look like the show is being shown at 1.732 times as fast as its normal rate. In the limit as your speed toward the TV approaches the speed of light, the rate at which the show looks like it’s being shown approaches infinity.

In general, if you’re approaching the TV at speed v, the apparent frame rate of the TV show is proportional to (1+v/c)/sqrt(1-v²/c²), where c is the speed of light. The same expression also works for the case that you’re moving away from the TV, in which case v is negative.

In reality, the colors of what's on the TV are affected if you're moving relative to the TV, so if you're moving too quickly, the colors would change so much that your eyes wouldn't be able to see them. MrRedact 08:18, 11 November 2007 (UTC)

Has any tried watching a TV while moving at a fraction of the speed of light? Most of the time the screen will be too tiny to see! Even at 0.000001% of the speed of light you will only get a few seconds viewing out of it! (joking here). Graeme Bartlett 20:23, 11 November 2007 (UTC)

Those who claim I made a mistake didn't read my reply - I specifically pointed out that you get the time dilation effect even after you take into account the fact that you are getting closer to it so that the light waves have a shorter distance to travel. SteveBaker 02:20, 12 November 2007 (UTC)

Not sure what you mean by "even after" -- the answer is that the frames will appear to move faster, not slower. By the way MrRedact's expression (1+v/c)/sqrt(1-v²/c² simplifies to the nicely symmetrical-looking ${\sqrt {\dfrac {1+v}{1-v}}}$ (where of course I'm using c=1, as is generally a good idea when talking about relativity).

Now in practice, of course, if you're going fast enough to notice any effect at all, you'll be going far too fast to process even a single frame from the TV. --Trovatore 02:28, 12 November 2007 (UTC)

Your confusion is consistent with misremembering what an "observer" is in relativity. In relativity, an "observer" isn’t one person at one location, but effectively actually a whole system of people spread throughout space, at rest relative to each other, who have a set of synchronized clocks. The time at which at event occurs is measured at the location at which the event occurs. So the difference in time between two events, which is what time dilation measures, doesn’t account for any time it takes for light to travel anywhere after either of the two events.

Suppose the TV is traveling at half the speed of light in the x direction relative to the lab frame, and suppose the TV has a mirror or two attached to it such that the screen can be seen by someone either in front of it or behind it. We won’t even need a Lorentz transformation for this; in the following, all coordinates are lab coordinates. Pick units such that c=1, and the period between frames of the show (as measured in lab coordinates) is 1. Pick the origin such that the TV starts to show frame number 0 when the TV is at x=0, t=0. At time t=1, when the TV starts to show frame number 1, the TV will be at x=0.5.

To someone at rest in the lab frame sitting at the origin, the light from the start of frame 0 will reach them at t=0, and the light from the start of frame 1 will reach them at t=1.5. To someone at rest in the lab frame sitting at x=0.5, the light from the start of frame 0 will reach them at t=0.5, and the light from the start of frame 1 will reach them at t=1. So the apparent frame rate as seen by the person in front of the TV is 3 times faster than the apparent frame rate as seen by the person behind the TV. This is consistent with the ratio 1.732/0.577 of the numbers given in my post above. MrRedact 07:29, 12 November 2007 (UTC)

Greenhouse Gases

Are Greenhouse Gases good for the environment or bad? —Preceding unsigned comment added by 70.171.192.2 (talk) 02:24, 10 November 2007 (UTC)

Have you consulted the article greenhouse gas? By themselves in moderate amounts they are not "bad" but in excess, at the rates that they are currently produced by human activities, they increase the greenhouse effect which leads to global warming. Which is bad. --24.147.86.187 02:31, 10 November 2007 (UTC)

We need to have some, otherwise the earth would be freezing cold all over. Carbon dioxide is essential for the life of photosynthetic plants. Graeme Bartlett 12:09, 10 November 2007 (UTC)

The 'normal' amount (about 0.038%) of CO2 is essential - less than that would be bad because the earth would freeze, more than that would be bad because of global warming. Right now, we have all the CO2 we need - and it's going up - so adding more greenhouses gas is definitely bad. Even if humans ceased to produce greenhouse gasses at all, the natural amount from animal respiration and volcanos would be plenty to keep the earth running OK. SteveBaker 18:31, 10 November 2007 (UTC)

I have no idea where the idea that global warming is bad came from. An increase in global temperature has a positive net effect on humanity. Look at climatic changes of the middle ages in europe and you will see that the warm periods were better recieved by the population than the cold ones. The main cause are reduced heating requirements and increased agricultural yields. Putting this to a global perspective: there is not a single area on earth to hot to live in. Too dry, yes, but not too hot. However there is a whole uninhabitable continent at the south pole, covered in mountains of ice.

So its good. The real problem is, at some point it will be too much. We don't know how the ecosystem reacts to really dramatic increases in temperature. It might be fine with 8° and collapse at 9°. Who knows? So the reason for reducing CO2 emissions is: we do not want to find this out the hard way. —Preceding unsigned comment added by 84.187.90.130 (talk) 00:49, 11 November 2007 (UTC)

WHAT! WHAAAT! Where have you been the last decade? This is quite the most ill-informed, unthinking response I've ever read on this topic! Firstly, the change in the middle ages was small compared to what we're talking about - also it was over fairly quickly and this time around it's going to be permenant. Secondly, while crop yields increase in the extreme latitudes, they decline sharply in the equatorial regions - the net effect will be disasterous. Reduced heating requirements are replaced by increased air-conditioning requirements (you've never lived in Texas have you?!). The antarctic region might become free of ice - but whats uncovered will be bare rock - no soil. The sharply increasing sea levels will drown all of the nice flat primo agricultural plains around the coastlines. You suggest that an 8 degree rise "might be OK" - but I can tell you that a 4 degree increase will be plenty disasterous. Please - do some reading of the proper scientific literature on this subject...or if (as it seems) you are unable to learn from these sources - rent a copy of "An Inconvenient Truth" - it's very comprehensible. SteveBaker 02:08, 11 November 2007 (UTC)

I don't think anyone is talking about an 8C rise. I think a 4C rise was on the tall end of the IPCC report for a 100 years. Sea level rise will probably affect the salinity of river deltas and a lot of food production areas but to say it will drown all the agricultural plains around the coastline is a little too pessimistic. As for AIC, any film that links smokestacks to hurricanes as AIC does on it's cover and in the material is not science. Stick to IPCC. Summary reports if you don't have time. Read about the discrepancies and conflicts if you do. Cloud cover and carbon sinks in the ocean are too big ones that have a lot of research and understanding yet to be done. --DHeyward 06:36, 13 November 2007 (UTC)

0.038% is the current CO₂ concentration, the pre-industrial level was about 0.027%. A question to the experts: How much higher would the equilibrium (glaciers need time to melt...) temperature be at 0.038%, compared to 0.027%? Icek 04:04, 11 November 2007 (UTC)

What do you mean? I thought I understood your question except for the glacier part. Glaciers have their own cycles for formation and melting. They've been melting on average for 10,000 years. Melting has been accelerated due to global warming but as I understand it, there was no equilibrium before. Glaciers can grow and shrink in both warming and cooling periods. --DHeyward 06:41, 13 November 2007 (UTC)

Well, I thought that the melting of the glaciers would be a heat sink for some time, keeping temperature lower as long as there are large glaciers. As the glaciers get smaller, the heat sink would get smaller, and the temperature would rise. Therefore I thought we have to think about the glaciers if we want to compute an equilibrium temperature. I see that the time for reaching such an equilibrium is quite long, maybe longer than climate cycles due to changes in Earth's orbit, obliquity, and equinoxes.

Restating my question: Averaged over the long-term climate cycles of the next few 100,000 years, how much higher would the temperature be if we stopped burning fossil fuel now? And how would the CO₂ concentration develop? Icek 07:45, 13 November 2007 (UTC)

Battery charge

1. How do rechargeable devices like mobile phones and mp3 players measure the amount of charge/energy left in the battery? Is it by measuring the terminal voltage? (which would be inaccurate due to polarization effects)? Or do they have ampere hour meters inside them?
2. When we operate them continuously the meter suddenly drops low and after switching off for some time the bar goes back up a little; which would explain the drop in voltage due to polarisation. Am I correct in assuming that?

59.93.9.23 05:35, 10 November 2007 (UTC)

Last I heard, the battery life indicator uses the voltage at the terminals. It is not accurate when it comes to predicting how long until the device quits. Each battery will be in a different stage of its life, and an older one will usually die sooner at, say, two bars. The graph is not linear even for any one battery, the change in voltage is very small, and current demand is unpredictable. You would need laboratory-standard equipment to make the thing at all accurate even under controlled conditions. I'm sure the phenomenon you mention in 2 is due to what is called polarisation, though the battery will drop some voltage internally under load anyhow. If it's right on the line between bars, you'll see a change upon power off just from that. The indicator will have some kind of anti-hunt designed in to keep the display from jumping around, so it will itself be slow to react. --Milkbreath 16:43, 10 November 2007 (UTC)

This is a good question, which I wish I had some more definitive answers to. (But since when has lack of definitive information stopped an armchair RD reader from speculating?)

There are at least four things a battery-charge indicator could look at in trying to make a determination of how much life the battery might have left:

1. Terminal voltage. A battery is, of course, a two-terminal device, so fundamentally, this is all you've got access to. Unfortunately, by definition, a battery is supposed to be a constant-voltage device, so its voltage shouldn't (and doesn't) change much over its lifetime. A theoretically ideal 1.5-volt battery would give 1.500000000 volts for its entire lifetime, then crash precipitously to 0 -- so a charge indicator looking only at voltage would have nothing to go on!
2. Of course, we don't have to limit ourselves to looking at instantaneous voltage; we can also look at rate of change (dV/dt). I'm pretty sure the voltage drops at different rates at various points during a typical (non-ideal) battery's discharge curve.
3. History. Top-end, full-featured batteries (such as the ones used in modern laptops) contain their own microprocessors. These can learn what that particular battery's discharge curve looks like, and use that knowledge to make a much better estimation of how much life is left based on where in the (now known) discharge curve it looks like we are.
4. Current draw. If the device has a built-in ammeter so that it can measure how much current is being drawn, and if it knows (perhaps based on historical information discovered by #3) what the battery's capacity in amp-hours is, it can make a very accurate estimation of how much life there is left. Of course, that estimate can and will vary if the current draw changes. I believe that's one reason why the bar can go back up. For example, I regularly notice my laptop's expected lifetime jump back up just after I stop doing something CPU-intensive.

Of course, this is all complicated by real-world considerations. Rechargeable batteries have a limited number of charge-discharge cycles, and can't hold a charge for as long the more cycles they've gone through, and are also prone to notorious "memory" effects. (I don't know how hard microprocessor-based batteries work to assess these effects; though they certainly could.) Also, most batteries show a sort of "rejuvenation" effect when they've been given a chance to rest after working hard (i.e., just like you or me). That's the other possible explanation for the bar-going-back-up phenomenon you noted. —Steve Summit (talk) 23:04, 10 November 2007 (UTC)

Thanks for the replies. Googling gives (what seems to be the terminology for this sort of thing) State_of_charge. Some websites and the wiki article say that in laboratory conditions they measure the concentration of the electrodes/electrolytes The results also include the microprocessor thingi. It seems to be called Charge_controller device. 59.93.9.69 04:35, 11 November 2007 (UTC)

Freezing Water Question

What would happen if you tried to freeze water it it were confined so it could not expand? For instance if a quantity of water were enclosed in a solid block of steel and the whole thing were subjected to low temperature and the water could not expand as it would when freezing, what would happen to the water? Would it stay liquid or freeze solid without expanding???? —Preceding unsigned comment added by 207.69.137.23 (talk) 05:57, 10 November 2007 (UTC)

Depends on where it is on the phase diagram. Freezing water in a confined space creates pressure on the order of several atmospheres (you can drive a go-cart with it) which may push it back into liquid phase, but again, it depends on both pressure and temperature. The way the ice crystals form is also dependent on this diagram, so you should really just check out the phase diagram article. SamuelRiv 06:11, 10 November 2007 (UTC)

Better yet, check out the responses from the last time we had this question. In brief, as the temperature is lowered, at first the water will remain liquid and generate an increasing pressure. If the temperature continues to be lowered, eventually it will freeze into a form (phase) of ice denser than the everyday kind. --Anonymous, 06:16 UTC, November 10, 2007.

anti inflammatory

do anti inflammatory medicine (gen-naproxen to be specific) affect your mood? —Preceding unsigned comment added by Morvarid rohani (talk • contribs) 08:08, 10 November 2007 (UTC)

In the list of side effects of naproxen (see here), no mood disorders are listed as frequently reported. However, depression has been reported in 1% to 10% of patients, and anxiety has been reported in <1%. Reports do not necessarily indicate causation. The fact that a drug causes a side effect in some patients does not mean that it is the cause in a specific instance; any question of whether a drug is responsible for a specific clinical condition should be discussed with a physician. - Nunh-huh 08:45, 10 November 2007 (UTC)

Bullets

Hi. How exactly does a bullet to the brain kill? Why do some people shoot the mouth, yet others shoot the temple? At what point does life cease? 203.124.2.43 11:44, 10 November 2007 (UTC) Adam

I used to have a great animation of a bullet going through the brain, bouncing off the other side of the skull and basically making a soup of the brain matter after bouncing around several more times, but I can't find it. When a bullet enters one side and exits the other, the entry and exit take a lot of compressed gases and brain matter with them making a small explosion in those areas, which can greatly increase trauma (that mostly depends on the bullet head shape). Sometimes bullet injuries leave people alive, like Manfred von Richthofen (the Red Baron) and Phineas Gage (a railroad spike, not a bullet). In Phineas's case, the spike damaged mostly one area of the frontal lobes, which govern a lot of higher-order reasoning and personality, but not so much in terms of low-order processing.

So let's get to the meat of your question: assuming a pointed bullet with enough speed to not bounce around the brain so that extra trauma is minimized, how do you kill someone? Shooting through the temple kills mainly by hitting the limbic lobe, which contains a lot of mid-order processing (thalamus), memory, and important regulatory glands. It is a guaranteed kill in some sense because you can destroy everything a person perceives about the outside world, whether or not their heart actually stops immediately. Shooting through the mouth is more appropriate because on the other side lies the brainstem and cerebellum, both of which control low-order function like breathing and heartbeat, with the brainstem being the connection of the brain to the body. So the kill in this case would be roughly instantaneous, though actual brain death would occur a bit later, because there would be some latent blood flow.

One more thing - severe brain trauma results in a couple of defense mechanisms by the brain. One is the coma, which for most bullet injuries would set in quickly, so the person would be incapacitated in any case. The other is a release of something (I forget what - I believe glucose) into the cell ether which results in a massive killing of brain cells. My neuroanatomy professor referred to it as a "self-destruct mechanism", but we don't know yet why it exists. Regardless, that can easily make brain trauma much more damaging than that of the actual impact. External links: [16] and [17] SamuelRiv 14:07, 10 November 2007 (UTC)

• 1. A brain can't absorp the shock of the bullet's entry without sustaining damage. 2. If that doesn't kill, bleeding will. - 87.211.75.45 19:32, 11 November 2007 (UTC)

Gold-labelled antibody = "fusion protein"

Is it appropriate to cover protein-non-protein ligations in the fusion protein article? I was just starting an article called conjugation (biochemical) and want to determine whether its warranted or not. Conceivably, one article should cover conjugation of proteins with other proteins, non-protein molecules, and possibly even non-protein-non-protein conjugations (none spring to mind). Perhaps the article protein engineering is more suitable for this? In which case, I can add a link at the conjugation disambiguation page? --Seans Potato Business 13:17, 10 November 2007 (UTC)

Wikipedia probably has many stubs such as Radioiodinated serum albumin and Biotinylation that could be collected into Protein labeling. I suggest not placing most "protein labeling" methods in the fusion protein article, but some fusion proteins are used to attach a label to target proteins. Sadly, Green fluorescent protein only seems to have an external link for the important topic of GFP fusion proteins. Maybe Conjugated protein could be expanded to include both natural and artificially conjugated proteins. I'd leave protein engineering to itself. --JWSchmidt 14:52, 10 November 2007 (UTC)

(EC) As a biochemist, I've never seen the term 'fusion protein' used to describe a non-protein combination. 'Fusion protein' is a bit more specific; it implies that a change has been made (insertion, replacement, and/or concatenation) to the primary amino acid sequence of the protein. This runs the gamut from adding a little tiny His tag through humanizing an antibody to attaching a whole additional protein (like GFP or a second part of an enzymatic complex). I would include under the 'fusion protein' definition the addition of domains that will dock particular prosthetic groups (a domain that binds a single metal atom, for instance).

For something like a gold-labelled antibody, you could use exactly that term. 'Immunogold', 'gold-tagged antibody', and even 'gold-conjugated antibody' come up a fair bit, too. For a general term to describe 'sticking something interesting to a biomolecule', 'conjugation' is probably as good a word as any.

As an aside on the topic of 'non-protein-non-protein conjugations' you need to remember the other important classes of biomacromolecules: DNA, RNA, and polysaccharides. All of them can be (and often are) modified with various sorts of labels (fluorescent, radioactive, immunogenic) to allow them to be studied. Conjugates that modify their function are also used sometimes, though this is perhaps less common. On a terminology point, the DNA equivalent to a 'fusion protein' would probably be 'recombinant DNA'. TenOfAllTrades(talk) 15:11, 10 November 2007 (UTC)

So perhaps conjugation (biochemical) would be a suitable umbrella for all conjugations, protein and otherwise. I don't have time for it now, but eventually... --Seans Potato Business 23:36, 10 November 2007 (UTC)

• I think that should read Conjugation (biochemistry) (so it avoids adjectives in the brackets). - 87.211.75.45 19:29, 11 November 2007 (UTC)

Neurotransmitters

In "Talk:Neurotransmitter#Neurotransmitter effects", I have described a recent experience involving dopamine, norepinephrine, and serotonin, attempting to link symptom clusters with specific neurotransmitter changes and extremes. Does my interpretation appear correct? Which receptors appear to have been preferentially overstimulated or understimulated? 66.218.55.142 15:13, 10 November 2007 (UTC)

DNA sequence around integrated HIV viral DNA attachment site?

Can anyone point me to books, published articles or other currently available research data which describe exactly what is the base pair sequence of integrated HIV viral DNA - I mean after the integrase process is completed, what is the DNA base pair sequence around those "attachment" sites? For example, what is the sequence when DNA in cell is cut in order to integrate viral DNA segment:
--TG...and_here_comes_HIV_DNA...CA--
--AC............................GT--
(This above is just example of what I'm looking for, those TGAC.. are just for example!) And then once the whole thing is integrated, what are those first few base pairs around both attachment sites? For example:
--TG...(U3RU5---HIV-DNA---U3RU5)...CA--
--AC...............................GT--
So, what are U3 and U5 of linear terminal repeat (LTR) attached to once the segment is integrated (the sequence of first few base pairs on both sides) and what does it look like together with U3 and U5 on both sides?? MANY THANKS to anyone who can point me to literature which covers this. --80.95.231.124 16:13, 10 November 2007 (UTC)

Have you seen HIV structure and genome? The literature at the end might be useful. SamuelRiv 17:34, 10 November 2007 (UTC)

Rocket speed

After how long does a space rocket reach 500 km/h and 1000 km/h ? Is there a graph of speed/time for rockets somewhere? I'm not very good with equations and I couldn't find the ones I thought necessary in the article rocket. Keria 17:54, 10 November 2007 (UTC)

Well, obviously, the time dramatically varies depending on the type of rocket. Something like the AIM-9 air-to-air missile accellerates at over 20g's. The space shuttle accellerates at a more pedestrian 3g's - so it piles on speed at roughly 30 meters per second every second. So we convert 500km/h into meters per second (500,000m/3600seconds = 138 meters/second) - takes roughly 138/30 seconds...4.6 seconds! To get to 1000km/h takes only 9.2 seconds. Well, in reality it's a lot more complicated than that - the various rockets start off accellerating fairly slowly because of the weight of all of the fuel - as the fuel burns off, the accelleration builds up - but at some point before the shuttle leaves earth's atmosphere, the speed becomes too high and the engines have to be throttled back to relieve the pressure on the spacecraft. Then as they get higher up and the air is thinner, they can go faster. When the SRB's detach, the spacecraft gradually slows down until (as yet more fuel is consumed), the engines can push the accelleration up again. Finally, the g forces start to get too large and again the engines have to be throttled back. Hence, in reality, the total time is going to be longer than 9.2 seconds - but still, it's piling on speed pretty amazingly fast. However, that AIM-9 rocket adds 200 meters per second every second - so it hits 500km/h within about two thirds of a second and 1000km/h in one and a half second! SteveBaker 18:23, 10 November 2007 (UTC)

You're a hell of a pedestrian. Hope I'll never run into you. —Preceding unsigned comment added by 84.187.90.130 (talk) 00:35, 11 November 2007 (UTC)

Robot Cars

What exactly is an autonomous robot car and how does it work? Could it work for a smaller or toy car? —Preceding unsigned comment added by 68.120.224.217 (talk) 19:27, 10 November 2007 (UTC)

• See DARPA Grand Challenge and links. --Sean 20:35, 10 November 2007 (UTC)

Currently, they take a standard car and add levers to push on the pedals and shift the shifter - also something to turn the steering wheel - those are hooked up to a computer that can therefore drive the car just like a human would. The tough part is that the computer has to be able to see where it's going and have enough intelligence not to do anything stupid like ramming the car into a brick wall. For this they use a combination of digital video cameras, and laser range finders (see Lidar - like Radar but with light instead of radio waves). Each individual technology is quite well known and understood - the tricky part is getting them all to work well together. We could make toys that did this - but the lidar sensors and the amount of computer power needed would be quite significant. But toys like the Aibo robotic dog are fairly sophisticated and can do some quite impressive things. It'll happen sooner or later. SteveBaker 00:24, 11 November 2007 (UTC)

You can do a lot with Lego Mindstorms, too. (I think; I still haven't given in and gotten a set for myself yet.) —Steve Summit (talk) 02:36, 11 November 2007 (UTC)

I have a few of the older sets - the newer ones are simultaneously better and less good for complicated reasons. But yes - you can easily build a "blind" robotic car using Mindstorms - but one that senses it's world and reacts accordingly (such as the ones in the Darpa Challenge) is MUCH harder and isn't really possible with the limited sensors that Mindstorms provides. It's relatively easy to do things like building a car-like robot and having it follow a black line made with electrical tape - or having it seek out light and park itself in a puddle of sunlight on your livingroom floor. But driving around in a complex environment without colliding with things and mowing down pedestrians...there is no way that a Lego Mindstorms machine could do that. It's a lot of fun though - and it's about on the limit of how complex something can be and still be considered a "toy" that kids could build and program. The most fun I ever had with it was making a pair of identical robots that could play "tag" in a darkened room. Each one had a bright light on the top and a 'bump' sensor that told it if it had been run into. One robot was programmed to seek light and the other to avoid it. When the 'bump' sensor detected that it had collided with something, the robot that was seeking light would send an infra-red message to the other robot saying (essentially) "You're It!" and switched from seeking light to avoiding it. When the other robot received a "You're It!" message, it would stop still, beep ten times at one second intervals and then switch from avoiding light to seeking it. The result of two of these little guys scurrying around the room was just hilarious to watch - but (and this is the ENTIRE problem here) the system only worked if neither of them went behind the sofa (killing the light seeking/avoiding behavior) or if they bumped into something else other than the other robot. I was able to add some sophistication to kinda/sorta fix those problems - but it rapidly becomes obvious that you need something better than a simple directional light sensor. Having a camera and lidar would help a lot! Some enterprising people were able to make a very crude lidar-like system using the infrared messaging system to send a message and looking for IR reflections in the light sensor. The strength of the returned reflection enabled some limited range measurement - but it was very crude. SteveBaker 02:51, 11 November 2007 (UTC)

Jupiter (the planet)

How was Jupiter formed and how old is it? —Preceding unsigned comment added by 72.38.227.206 (talk) 22:07, 10 November 2007 (UTC)

You can read about it at Jupiter. —Steve Summit (talk) 22:21, 10 November 2007 (UTC)

...which, I'm sorry, doesn't really answer your question. Anybody have a better reference? (There's a bit of information at Solar System.) —Steve Summit (talk) 22:27, 10 November 2007 (UTC)

Planetary formation (which, for some reason, is currently a redirect to "Nebular hypothesis") may answer this and the following question in more (perhaps too much) detail. In any case, the best one can say about the ages of the planets is that, as we currently understand planet formation, they're all about equally old, and slightly younger than the Sun itself. The reason it's hard to even define an exact age for a planet is that, after the initial aggregation of small planetesimals from the protoplanetary disk, they are believed to have undergone an "oligarchic growth" phase where the proto-planets of various sizes grew by colliding and merging at random. Thus, it's hard to say which collision was the one in which the resulting planet became the one we know today. There's no specific start or end to the oligarchic growth phase either; while the biggest planets eventually settled into more or less stable and non-colliding orbits, the smaller, more numerous bodies continued to collide with them and each other at gradually decreasing frequencies, as they still do to this day.

Also, it's worth noting that, for gas giant planets like Jupiter, there are two competing theories of their formation. The one that, as far as I can tell, seems to be enjoying the greatest popularity at the moment is that they started out like the smaller planets, as solid bodies growing by collisions, but eventually grew big enough that their gravitational pull could directly capture and hold down gas from the surrounding protoplanetary disk, leading to runaway growth as more and more gas fell down upon the initial rocky core. This didn't happen with the inner planets because, by the time they grew big enough, the solar wind had already blown most of the gas away from that part of the solar system. The alternative hypothesis, however, is that the gas giant planets formed directly from the gas disk without any solid "seed"; according to that theory, an eddy in the protoplanetary disk simply pulled enough gas together that its mutual gravitational pull caused it to collapse, much as stars are believed to form. Neither hypothesis is by no means disproved yet — it's even possible that gas giant planets can and do form by both mechanisms. —Ilmari Karonen (talk) 00:07, 11 November 2007 (UTC)

The planet Mars

How old is Mars? —Preceding unsigned comment added by 72.38.227.206 (talk) 22:15, 10 November 2007 (UTC)

You can read about it at Mars. —Steve Summit (talk) 22:21, 10 November 2007 (UTC)

...which, I'm sorry, doesn't really answer your question. Anybody have a better reference? (There's a bit of information at Solar System.) —Steve Summit (talk) 22:27, 10 November 2007 (UTC)

I presume Mars must have been formed at roughly the same time as the Earth - roughly 4.5 billion years ago. (See Formation and evolution of the Solar System and Age of the Earth.) We haven't studied the geology of Mars well enough to know for sure. But the age of the Earth is something of a compromise between the age of the oldest rocks we can find (3.9 billion years) and the age of the solar system (4.6 billion years). It's very likely that even after we have crawled over every inch of Mars looking for old rocks, our answer will be about the same. SteveBaker 00:17, 11 November 2007 (UTC)

Part of the problem with rock ages is that rocks form and reform due to subduction of the Earth's crust and the much different environment of early Earth, so today's rocks are going to be younger than Earth as a whole. Also note that most of our aging techniques won't work on liquids like magma. SamuelRiv 01:27, 11 November 2007 (UTC) Addendum: note there is no plate tectonics on Mars, though there is volcanism. Thus somewhere deep under the surface may be a rock as old as the solar system. SamuelRiv 01:28, 11 November 2007 (UTC)

I have some quibbles with that. Firstly, we know for sure that the young Mars had volcanoes. Olympus Mons - for example - is the largest extinct volcano in the known solar system! If Mars once had a liquid core sufficiently close to the surface to allow volcanism then it seems entirely possible that it once had plate tectonics too. Secondly, despite the ravages of plate tectonics, the date of 3.9 billion years for the minimum age of the earth comes from dating zircon crystals from Western Australia - so despite subduction and volcanism - we still have some pretty old rocks lying around at the surface where we can find them. SteveBaker 02:30, 11 November 2007 (UTC)

I addressed the issue of volcanism, and note the volcanoes on Mars are all shield volcanoes (like Hawaii), and thus are not dependent on plate tectonics. I'm aware that very old rocks have been found on Earth - I'm just addressing why they might be hard to find, and indeed why one as old as the Earth may be impossible to find. SamuelRiv 16:23, 11 November 2007 (UTC)

Cause and Effect

Is it right that not one thing in the Universe hasn’t obeyed the Laws that govern it? If EVERYTHING obeys the rules of Cause and Effect is it not true that everything happens for a reason? If this is true it would seem that nothing can be random and everything is predicatbale. Sorry if this is the wrong place to ask such a question. —Preceding unsigned comment added by 71.150.248.92 (talk) 22:34, 10 November 2007 (UTC)

This topic has dogged philosophy and religion since time out of mind. There's a bunch of stuff on the topic at Causality, Determinism, and Free will. It seems obvious that events are caused by other events. I wouldn't be typing this right now had you not asked the question. But it seems just as obvious that we are not robot-like automatons. I feel as if I am making choices about the words I type. The conflict between these two obvious things is, I think, at the heart of most religions and much of philosophy. Personally, I think that something must be wrong with the question, since people have been asking it for thousands of years and still end up in paradox. Pfly 22:57, 10 November 2007 (UTC)

For many interesting physical systems, predictability is not possible because even small variations in where you are now can result in large changes in where you will be. See Chaos theory. --JWSchmidt 23:29, 10 November 2007 (UTC)

Well, let's be really careful here:

• Is it right that not one thing in the Universe hasn’t obeyed the Laws that govern it? - Yeah - that's right. If some 'law' is ever disobeyed then it isn't a law...so this is true by definition. Is it the case that some of the things we humans believe are 'laws' are wrong? Yes - it's really unlikely that everything we think we know is 100% correct. Newton's "laws" of motion were proven wrong by Einstein's relativity.
• If EVERYTHING obeys the rules of Cause and Effect is it not true that everything happens for a reason? - "Cause and Effect" is not a law. To the contrary, many quantum effects do not follow 'cause and effect' and are fundamentally unpredictable. If you irradiate an atom and stuff some extra neutrons into it - it will eventually decay back down to it's original state by emitting a neutron. When will that happen? Well, we don't know, we cannot know - it's truly, utterly random. Where is the "cause" of that neutron being emitted? There isn't one.
• If this is true it would seem that nothing can be random and everything is predicatbale. - To the contrary, at its heart absolutely everything is completely random and unpredictable. The only thing that makes the universe seem stable and follow nice cause-and-effect rules is the effect of statistics. We don't know when one irradiated atom will decay - but we know with great precision how a kilogram of atoms will decay. We can't know the exact position of an electron - but we can deduce the position of a planet orbiting a star a hundred light years away by measuring the tiny wobble it induces in that star. The universe on the large scale obeys rules - but at the small scale, it's truly random. But the large scale effects are pure statistics. It is perfectly possible (although exceedingly unlikely) for a grand piano to appear out of nowhere in your living room right now. It's only statistics that enables us to say that this "Won't ever happen".

Look at it like this, if you flip a coin, you have no idea whether it'll come up heads or tails. If you flip 100 coins, you can be pretty sure that between 40 and 60 heads will show up - but predicting that you'll get 50% heads is a bit 'iffy'. If you flip a million coins, you can be quite sure that between 499,000 and 501,000 heads will show up - so a 50% prediction is a fairly accurate 'law'. If you flipped as many coins as there are atoms in a grand piano, your prediction of 50% heads would be precise to within one part in a billion billion billion (probably much better than that actually). In effect, you have a cast iron "law" of nature that says "when you flip coins you absolutely always get exactly 50% heads" - but that's not even close to being true for four coins - and it's POSSIBLE to flip a million coins and for them all to come up heads...it's just so unlikely that on a large scale, it's not going to happen. That's how our "large scale" laws operate. They are so accurately true that we can rely on them - even though at their heart, they are relying on completely random events.

• Sorry if this is the wrong place to ask such a question. - This is the perfect place to ask this question!

SteveBaker 23:58, 10 November 2007 (UTC)

Thanks for all the replies. Very interesting answers. —Preceding unsigned comment added by 71.150.248.92 (talk) 02:45, 11 November 2007 (UTC)

I have read alot of extremely well-researched, wonderfully articulated replies on the Science Desk, but SteveBaker's reply to this ultimate of all quandries is truly amazing. The idea that science, even at its finest, boils down to statistics, and that those statistics when viewed from an appropriate macroscopic level may be termed as "laws" is an idea I've been aching to come across. Thank you! Sappysap 04:05, 11 November 2007 (UTC)

Er...wow! Well, thanks! Before we get carried away though - the critical 'take away' point here is that while these macroscopic laws are "only" statistical, the magnifying effect of the sheer quantity of particles on the certainty of the result makes the resulting law quite utterly cast-iron. You cannot and must not take from my explanation the idea that the macroscopic laws are broken routinely because of this statistical stuff. On human scales - they absolutely are not. The probability of anything measurably different from what we expect actually happening is so astronomically small that this makes it impossible for any practical measure whatever. So "certainty" is still present at our scales. But when we deliberately make the small scale visible on the large scale, weird stuff can happen. Listen to the individual clicks of a Geiger counter picking up background radiation (Image:Geiger calm.ogg for example) - each click is the result of the decay of a single atom producing a single neutron. Guess what? It's utterly random - you can clearly hear that - there is fundamentally no way to predict when the next click will happen. SteveBaker 05:43, 11 November 2007 (UTC)

Well, I'm not listening to a Geiger counter per se, but just now I happen to be listening to "Radio-Activity", by Kraftwerk, which starts out with the sound of one. Weird coincidence, or subtle causality? (You be the judge. :-) ) —Steve Summit (talk) 06:01, 11 November 2007 (UTC)

Responding here to Steve's claim that "certainty is still present at our scales" except when "we deliberately make the small scale visible on the large scale". I don't believe that's true. The effect of quantum indeterminacy can easily be blown up to a macroscopic scale by processes not requiring our deliberate intent, by any system that chaotically amplifies small differences with positive feedback. Like weather. So I think, for example, that the question "will it rain in Dallas on the afternoon of July 17, 2063?" is truly non-determined; quantum uncertainty now, on a microscopic scale, will have been amplified to different macroscopic answers by then.

He's certainly correct that there are questions we can ask where the answers are quite deterministic for practical purposes. But those are the questions where small differences tend to cancel out, rather than being amplified. --Trovatore 22:00, 11 November 2007 (UTC)

You're talking about chaos theory. The thing about that is that it produces infinite sensitivity on initial conditions. Chaotic events would be unpredictable as a practical matter (and perhaps as a theoretical matter too) no matter whether quantum-level randomness existed or not. SteveBaker 01:53, 12 November 2007 (UTC)

But the point is that, because of the quantum-level stuff, whether it will rain in Dallas on that afternoon is (I think) unpredictable even in principle, because not enough information exists to determine it. That's different from deterministic chaos, where the only issue is whether you have enough computing power available to run the simulation. --Trovatore 02:00, 12 November 2007 (UTC)

NO! That's not true. It's not about computing power. I can explain this but we need a simpler concrete example. The weather is too complicated to discuss - let's talk about a simpler (but still deterministic and still chaotic) system. This is one of my favorites because it's easy to imagine:

First, the equipment: Take a couple of small, strong magnets and place them about six inches apart in the middle of a large sheet of paper your desk. Now hang a magnetic pendulum bob a few inches above the magnets on the end of a nice long string suspended from the ceiling. You also need a red and a blue crayon. OK - so here is the experiment:

Hold the pendulum over some point on the paper, release it and after it swings around a bit and if the magnets are strong enough, the pendulum will end up hovering over the center of either one or the other magnet. Colour that 'release point' with a small red dot if the pendulum ended up over the right-hand magnet - colour it blue if it ended up over the left-hand magnet. Repeat this experiment for every point on the paper so it's completely covered in red and blue dots.

So what red/blue pattern results? Well, when you release the pendulum near the right magnet the result is always that the pendulum swings immediately over that magnet - so there is obviously an area around the right magnet that ends up red, and an area around the left magnet that ends up blue. Now, if you hold the magnet a bit further off to the right - beyond the righthand magnet, the pendulum will fly right over the righthand magnet and swing over to the lefthand one - by then it's lost enough energy due to air resistance that it'll stop over the lefthand magnet. But you can imagine that from some places the pendulum loops around one magnet then the other crazy swings until it finally loses energy and winds up over one or the other.

So you can imagine a fairly complex pattern of red and blue on the paper.

Now this magnetic pendulum setup is 'chaotic' (in the same way that the weather is). If you crunch the math on this, the actual mathematical pattern you wind up with is a fractal - something like the Mandelbrot set. There are regions of our red/blue pattern that are in big solid patches (like immediately around each of the two magnets) - but there are regions where the red and the blue is all mixed up in whorls and patterns of great complexity. Write a computer program to generate this pattern and you can zoom into these patterns and you see more patterns, you can zoom in deeper and deeper into that map - and in some areas you'll keep on getting more and more red/blue patterns no matter how tightly you zoom. The image is infinitely complex...fractal...chaotic.

What is the physical meaning of this infinite complexity of red and blue dots? It means that if you start the pendulum over one of those chaotic regions and release it, the magnet it will end up over is very sensitive to where you started it from. Move a millimeter to one side and the answer may be different. Move a millionth of a millimeter to one side and the result will be different, move the width of a hydrogen atom to one side and you'll get a different answer. In fact, move an INFINITELY SMALL distance to one side or the other and the pendulum may end up over the other magnet. The result is that moving the pendulum by (1/infinity) meters can change the answer...but (1/infinity ) is zero (well, kinda - mathematicians might argue it 'approaches' zero - but the result is the same)...so if you move the pendulum by zero distance, the answer can change. It's deterministic - in that there is no randomness in the equations - but you need infinite precision to calculate it - and even if you had that, you still wouldn't get the right answer because displacing the initial position of the pendulum by 1/infinity meters changes the answer.

CONCLUSION: You don't need quantum effects to get a random answer - you don't even need an inaccurate measurement of the initial position because an error of (1/infinity)% is enough to change the answer. The result is independent of computer power or precision.

SteveBaker 15:46, 12 November 2007 (UTC)

Um. The boundary between the red and blue regions may well not be computable. But I think you'll find, in the deterministic idealization of the pendulum problem, that for any ε greater than zero, there's a computer program and a finite amount of information about the initial conditions that -- given sufficient time to run and resources -- would give you the right answer for at least a proportion of 1-ε of the space of possible initial conditions. Which is not true for the quantum version of the same problem.

Computability is beside the point here anyway (or at least, beside my point). In the deterministic case, there exists a function, whether you can compute it or not, that takes the initial conditions and returns the final answer. In the quantum case, no such function even exists,computable or not. --Trovatore 19:47, 12 November 2007 (UTC)

That's true - but you miss the point. For any given starting point, even if you could compute whether to label it red or blue, the problem is that in some areas of the map, the individual red and blue dots are INFINITELY small. So the information from some theoretical computation would be utterly useless because nothing can be positioned infinitely accurately (irrespective of quantum theory). For every red dot in one of these chaotic regions, the distance to the nearest blue dot is zero. But worse, the answer isn't computable because to arrive at the right answer you need infinite precision - that requires an infinite number of bits of storage and (on a finite computer) infinite computation time.

Chaotic systems are deeply weird - even in a 'classical' universe. In a practical quantum universe, there is clearly no way to position anything with anwhere near enough precision and still keep it stationary because of the uncertainty principle. But Newton and Einsteins idea of a 'clockwork universe' where everything is ultimately predictable is blown away by chaos theory every bit as efficiently as by quantum theory. Better actually because you can show the correctness of chaos using pure mathematics. Quantum theory still requires experimental evidence and Einsteins idea that there might be an 'underlying certainty' is really tough to disprove. SteveBaker 21:22, 12 November 2007 (UTC)

SteveBaker 21:22, 12 November 2007 (UTC)

Are you claiming that, in the deterministic version, the intersection of the topological closure of the red set, with the closure of the blue set, has positive Lebesgue measure? I can't refute that off the top of my head but I think it's most unlikely. Whereas if that intersection has measure zero, then the up-to-epsilon computability that I mentioned earlier would be true, and would probably match the "clockwork universe" idea well enough (though admittedly in a completely impractical way). --Trovatore 22:53, 12 November 2007 (UTC)

I don't know whether there is a positive Lebesgue measure - but that's not necessary. We don't know whether the Mandelbrot set has a positive Lebesgue measure either. That doesn't prevent it from being infinitely crinkly which is all that is needed in order to guarantee that for some areas of the diagram, there are areas where we have infinite sensitivity to initial conditions. SteveBaker 00:15, 13 November 2007 (UTC)

Sure, but by itself that's not very interesting. Balance a pencil on its point -- will it fall to your left or to your right? Even in the deterministic version of the problem there's a boundary point, where you have your infinite sensitivity. But for almost all (in the sense of Lebesgue measure) possible positions of the pencil, in the deterministic version, you can predict where the pencil will wind up, given sufficiently accurate measurement. I don't think this would have upset Newton or Einstein too much. --Trovatore 00:28, 13 November 2007 (UTC)

From the question: To the contrary, many quantum effects do not follow 'cause and effect' and are fundamentally unpredictable. Maybe my understanding was wrong, but this isn't how I interpreted quantum mechanics. Rather, as I learned it, the apparatus for measuring the effect operated on the cause and therefore it was impossible to distinguish the two cause and the measurement. The proccess of observing affects what is being observed. In quantum mechanics it really did matter if there was someone there to hear the tree fall in the forest. Entanglement and the wave/particle duality experiments highlight this. --DHeyward 07:17, 13 November 2007 (UTC)

November 11

Physics and Ancient Greece

I remember my grade school science teacher once telling us that Ancient Greece not only knew the world was round, but more amazingly they also knew its rough diameter. The ancient experiment took place on a wide and very flat plain; on it, two towers spread miles apart. The towers would signal each other in daylight and then quickly measure how long the shadows of each tower fell on the plain. That was all they needed to roughly measure the size of the world. I liked this science teacher quite alot and so I almost hate to ask: is an ancient experiment of this kind roughly possible? A lesser question: without too much research, is there any historical corrobaration for the rough diameter of the world being published more than two thousand years ago? Sappysap 00:16, 11 November 2007 (UTC)

Eratosthenes is the first known to have calculated the circumfrance of the earth. He did conduct an experiment very similar to what you describe to estimate the curvature of the Earth. His estimate was probably a bit off but pretty good for a first shot! You can look at History of geodesy for more discussion of his method and later methods. --24.147.86.187 00:26, 11 November 2007 (UTC)

Yep - the numbers that these techniques could come up with would be very approximate - but they could certainly prove that the earth is round simply by noting that the further North you went, the longer the noon-time shadow is - but the length of the shadow doesn't change when you go East/West. I don't think they used two towers that could see each other though. What I thought they did was to measure the length of the shadow at noon for two locations hundreds of miles apart on the same day. Because they knew (roughly) the North/South distance between those locations, they could do the calculation without requiring communications between the towers. They knew that at noon the shadow was at it's shortest - so precise timekeeping was not needed. Not requiring the two towers to be able to see each other means that they can be a lot further apart - which makes the whole calculation much more accurate. But the observation that the length of the day is more variable at higher latitudes is theoretically enough to allow an observant person to deduce that the earth must be round. SteveBaker 00:42, 11 November 2007 (UTC)

According to the Eratosthenes article: "The exact size of the stadion he used is argued by those who suppose he got it right; but the common Attic stadion was about 185 m, which implies a circumference of 46620 km, i.e. 16.3% too large."

I would consider an accuracy of 1/7 very impressive for someone who did this calculation over 2000 years ago.

Eratosthenes decided to use two cities instead of two towers. The Sun shined directly down a well in one city on the noon of every summer solstice, it was at the zenith at these times. In the other city, he measured the noon sun's elevation during another summer solstice. This would give the cities' latitude difference, and the Earth's circumference can easily be computed if the distance between the cities is known. --Bowlhover 07:24, 11 November 2007 (UTC)

That can't be exactly true. The sun only shines "directly" down a well when you are near the equator. Greece is at roughly 38 degrees north - the earth's axial tilt is 24 degrees - so even at mid-day on the summer solstice, sunlight would shine down the well at an angle of roughly 14 degrees to the vertical. In the end, the problem boils down to the precision with which you can measure the angle of the sun (or the length of a shadow or the depth to which sunlight penetrates a well - all of which amount to the same thing) - and the precision with which you can measure the north/south distance between your two points. Picking two cities far apart makes accurate measurement of the distance between them tough - but reduces your dependence on the accuracy of sun's elevation. Picking two points closer together gives you better precision on the distance between them - but the precision with which you measure the angle of the sun becomes vastly more critical. SteveBaker 14:27, 11 November 2007 (UTC)

Minor correction - you don't have to be exactly on the equator for the sun to be at the zenith at noon on certain days of the year - you only have to be between the Tropic of Cancer and the Tropic of Capricorn. One of the end-points of Eratosthenes baseline was Syene or modern-day Aswan, which is slightly north of the Tropic of Cancer. Our article says:

The latitude of Aswan – 24° 5′ 23″– was an object of great interest to the ancient geographers. They believed that it was seated immediately under the tropic, and that on the day of the summer solstice a vertical staff cast no shadow, and the sun's disc was reflected in a well at noonday. This statement is only approximately correct; the ancients were not acquainted with the exact tropic: yet at the summer-solstice the length of the shadow, or 1/400th of the staff, could scarcely be discerned, and the northern limb of the sun's disc would be nearly vertical.

Eratosthenes presumably knew this bit of "folklore" about Syene, and he took his home town of Alexandria as the other end of his baseline, so he could estimate the size of the Earth from measurements made in his own garden. Gandalf61 16:54, 11 November 2007 (UTC)

Yes, Aswan is in Egypt and not Greece. Using Aswan was logical because if the sunlight illuminated the bottom of a deep well, the Sun's altitude could accurately be determined as 90 degrees. If an accurate data point exists, why not use it? --Bowlhover 17:49, 11 November 2007 (UTC)

One more point: the Earth's axial inclination is not exactly constant, owing to tidal effects. In the time of Eratosthenes, it was a little larger and therefore the Tropic of Cancer was farther north, at 23°43'. Syene still wasn't exactly on it, but it was closer than would be the case today. --Anon, 06:33 UTC, November 12, 2007.

The funny part is that Posidonius repeated Eratosthenes calculation, via slightly different means, and came up with essentially the same result -- and a fairly accurate one at that -- but then revised his calculations such that the circumference was about a third to small. And this figure got incorporated into Ptolemy's Geographia which, along with medieval calculations by Islamic geographers that tended to support the smaller figure, greatly influenced Christopher Columbus's theory of Asia being located approximately where the Americas are. History is funny. Pfly 07:34, 11 November 2007 (UTC)

The bottom line: Eratosthenes and other greeks know perfectly how to estimate a sphere's diameter. The problem for them was that the instruments they had at their disposal were some dracmas and a man's footsteps. But apart from those minor details, they made perfect scientists. --Pallida Mors 76 22:51, 11 November 2007 (UTC)

One point often omitted in connection with Eratosthenes's estimate of the size of the Earth is that the calculation is only correct if the Sun is known to be at a great distance. Say A is Alexandria, B is Syene, S is the Sun, and C is the center of the Earth; at the time of measuring, SBC is known to be a straight line, so points SAC make a triangle with point B on side AC. The angle of 7.2° between the Sun and the vertical, as directly measured at Alexandria, is the supplement of angle SAC. When we say that AB forms an arc of 1/50 of the Earth's circumference, we are assuming that angle ACB is also 7.2°!

But in fact angle ACB = ACS = 180° - SAC - ASC = 180° - SAC - ASB = (supplement of angle SAC) - ASB = 7.2° - ASB. However, since the Sun is 93,000,000 miles away, angle ASB is only about 0.0003° and it is safe to treat ACB as having been measured as 7.2° also. If we believed that the Sun was only 25,000 miles away (and therefore about 230 miles in diameter), then angle ASB would be about 1.1°; we would then compute ACB as 6.1°, producing an estimated figure of 29,500 miles for the Earth's circumference. You could also get a 7.2° change of Sun angle over 500 miles if the Earth was flat and the Sun was about 4,000 miles up!

Fortunately, Eratosthenes did believe that the Sun was at a great distance, although it's not clear exactly how great, so his calculation went the right way on this. (Perhaps someone could work some of this into the article on him; I don't have time now.)

Moving onward from the way Eratosthenes actually did it, let's talk about the situation the original poster remembers the teacher describing: two tall towers in sighting distance across a level plain, with the length of each one's shadow observed at the same time, using light signals to synchronize their observations.

The first point is that towers in ancient times weren't built all that high. The biggest Egyptian pyramids were a few hundred feet. Even if a tower 500 feet high was available, the horizon would be only 28 miles away. Therefore even if we imagine that two towers of that height were used, they would have to be no more than 56 miles apart. This means that the important angle formed between the two towers and the center of the Earth would be about 0.8° instead of 7.2°, and therefore a good deal harder to measure with sufficient precision. If we imagine lower buildings,

Further, the story referred to using the shadow of the tower itself. In ancient times nobody was building vertical-sided buildings anywhere near that high. If a building is a pyramid, or in general any shape without vertical sides, you can't measure the length of its shadow by just starting at the base of one wall; you have to measure from a point below the highest part of the tower, presumably well inside the building. So this would introduce additional error. I don't know what the maximum height for a vertical-sided building was in ancient times, but if it was say 100 feet, then the maximum distance between two such buildings would be about 25 miles, requiring an angle of 0.4° to be measured.

Further, the story refers to a signal passed between the buildings using light, and this would have to be done in the daytime, so lighting a fire wouldn't serve. It is difficult to imagine what could be done fast enough to serve as a good signal that could be plainly seen 25 or 50 miles away without such a thing as a telescope. A mirror reflecting the Sun ought to be visible at that distance, but impossible to aim accurately so it could be seen at the other tower. Perhaps a big sheet of cloth like a sail could be hung over the tower and then let fall, but I don't think it would be practical to make one big enough, which would also have to contrast with the tower. At 25 miles a cloth 100 feet square would appear only 1/10 the width of the full Moon. And if the towers are at the maximum distance for sighting each other, then only the top bit of each tower is visible from the other.

--Anonymous, 06:33 UTC, November 12, 2007.

The OP's story sounds like a strange mix of Eratosthenes, the use of Theodolites in the Principal Triangulation of Great Britain (and of India, which doesn't seem to have a page), and Semaphores... or something. Pfly 09:13, 12 November 2007 (UTC)

Are you looking for Great Trigonometric Survey? —Steve Summit (talk) 14:58, 12 November 2007 (UTC)

Ah ha, yes that's it. If I recall right, the project sometimes involved the building of towers in sight of one another, upon which theodolites were placed to survey via triangulation methods. And interestingly enough, that page says the project was was responsible for the first accurate measurement of a section of an arc of longitude, which relates back, sort of, to the circumference of the Earth. Not quite Ancient Greece though. Pfly 16:37, 12 November 2007 (UTC)

That's quite the overstatement -- I daresay Jean Delambre and Pierre Méchain would have something to say about it! I mean, the Indian survey may well have been more accurate than their earlier work, but still! --Okay, fixed now. (See also "The Measure of All Things" by Ken Alder, and if you read French, fr:Figure de la Terre et méridienne de Delambre et Méchain.) --Anonymous, 06:14 UTC, November 13, 2007.

does inhibition of PKC-β activity decrease pigmentation in vivo?

how? is it permanent? —Preceding unsigned comment added by 81.99.212.22 (talk) 01:03, 11 November 2007 (UTC)

According to this article, PKC-β phosphorylates and activates tyrosinase and "topical application of a selective PKC inhibitor reduces pigmentation and blocks UV-induced tanning in guinea-pig skin". They also discuss regulation at the level of transcription. --JWSchmidt 01:17, 11 November 2007 (UTC)

Feces - taste like what?

I've always wondered what human feces (faeces) taste like.

I'm aware that this might be a strange question. I also realize that I could easily provide my own answer, but I'd prefer to leave it to someone with an interest in coprophagy. —Preceding unsigned comment added by 222.155.51.145 (talk) 07:40, 11 November 2007 (UTC)

Most of the taste sensation is due to the smell. SO I think you could imagine the experience. But you would have the texture and tongue taste as well. The average 1 year old probably can remember the experiencem(but not me)! Graeme Bartlett 10:10, 11 November 2007 (UTC)

Without having performed any OR on the matter, I can nevertheless confidently assert that they taste like shit. —Steve Summit (talk) 14:23, 11 November 2007 (UTC)

After digestion, very little that stimulates taste receptors should remain. Probably the only recognizable taste would be salt, but no saltier than blood. 66.218.55.142 14:40, 11 November 2007 (UTC)

I was under the impression that it had a spongey texture, although I cannot remember where I encountered this gem of information. [18] will perhaps help you on your enquiry. (Really, don't follow that link unless you have a strong stomach). Lanfear's Bane | t 15:08, 11 November 2007 (UTC)

For your sake and for mine, let us hope that that is peanut butter. Can I wash my eyes now? --Russoc4 16:47, 11 November 2007 (UTC)

commercial radioisotope

What is a commercial radioisotope? —Preceding unsigned comment added by 144.137.98.219 (talk) 10:17, 11 November 2007 (UTC)

It is a radioactive isotope that you can purchase as a standard product, such as ¹³¹Iodine —Preceding unsigned comment added by Graeme Bartlett (talk • contribs) 10:52, 11 November 2007 (UTC) or tritium. Graeme Bartlett

asteroid belt

if some spaceship tries to cross the asteroid belt, then instead of by passing through it, can it go above it and cross the belt?SidSam 10:34, 11 November 2007 (UTC)

A spaceship could go above or below, but asteroids occasionally will orbit at an inclined angle and stray into that space too. The belt is actually very thin and the chances are that a spaceship will fly through and not be impacted. The problem is that more fuel is needed to go outside the eccliptic plane, and then back into it. Space ships always scrape by on the minimum fuel, so such maneuvers are unlikely unless there is a reason to go up and out there. Graeme Bartlett 10:56, 11 November 2007 (UTC)

I heard it's so widely spaced that if you were at one asteroid, you wouldn't even be able to see another asteroid with naked eyes. So passing right through it seems pretty safe. 64.236.121.129 15:08, 12 November 2007 (UTC)

Tbe asteroid belt is more like a flat ring around the sun - like one of Saturns rings - so you could certainly go around it. But the rocks within it are widely spaced - so it's pretty safe to travel through it as though it wasn't there. SteveBaker 14:04, 11 November 2007 (UTC)

The scatter-graphs at asteroid family may suggest how much like Saturn's rings the asteroid belt is not. —Tamfang 22:46, 12 November 2007 (UTC)

Aldol

In the aldol condensation of acetone, mesityl oxide is created. What then, if anything, prevents a further acetone molecule from adding on to the other side of the product, resulting in an endless chain of carbonyls? Or, what prevents the mesityl oxide from adding onto another molecule of acetone, creating a symmetric compound with another isobutene group? What about endless Michael reactions at the double bond? Could't you theoretically just keep making one infinitely larger compound, as long as there are alpha-hydrogens and/or alpha-beta double bonds? --Russoc4 14:56, 11 November 2007 (UTC)

Yes, that's called polymerization. Apparently it can be a serious problem when you don't want to make polymers, because it deactivates the catalyst.[19] [20] That second one says "The active sites for aldol condensation are the same as the active sites for polymer production.". There are even patented methods to inhibit the polymerization.[21] —Keenan Pepper 17:13, 11 November 2007 (UTC)

So then, disregarding any Michael reactions, these [22] would be the possible aldol condensation products? What do you think would happen if I added acetone to a concentrated NaOH solution and heated it? Would that polymer be a likely outcome? --Russoc4 18:01, 11 November 2007 (UTC)

But if you read the page on mesityl oxide, it points out that further condensation yields isophorone, which is a cyclic product. Six-membered rings like that of isophorone are pretty stable and will ressit further attack. Delmlsfan 02:02, 12 November 2007 (UTC)

Heisenberg t-shirt

I am pretty sure I have seen an image containing the Heisenberg uncertainty principle ($\Delta x\Delta p\geq \hbar /2$) and the text "free will". I thought it was a t-shirt or sticker from either xkcd or ThinkGeek, but can't find it. Does anyone know where I might have seen it? —Bromskloss 20:38, 11 November 2007 (UTC)

Not sure, but I'd like a shirt with that inequality and the text "mathematical consequence of a probability theory in the complex field" or maybe "If you get the math, it's obvious". SamuelRiv 22:06, 11 November 2007 (UTC)

Well, it's a trivial consequence of the canonical commutation relation, but is it obvious that the CCR must hold? Algebraist 22:46, 11 November 2007 (UTC)

In the plain math, it comes from the Fourier transform of a waveform, where you find position and momentum space have fundamental uncertainty in deriving one knowing the other. SamuelRiv 22:59, 11 November 2007 (UTC)

So you're claiming it's mathematically obvious that systems are described by wavefunctions? Algebraist 23:16, 11 November 2007 (UTC)

I'm almost positve you can cross XKCD off of the list. As far as I know, they have made a joke of everything nerdy except for the Heisenberg uncertainty priniciple. However, I did find another Heisenberg shirt. Paragon12321 00:16, 12 November 2007 (UTC)

It seems I'm out of luck here. Anyway, you have heard this one, haven't you?:

Police officer: "Have you any idea how FAST you were going back there?"
Werner Heisenberg: "Nope, but I knew EXACTLY where I was!"

:P —Bromskloss 08:26, 12 November 2007 (UTC)

I don't know about a tee-shirt, but as for comics, see Casey and Andy strip 128, and stripts 247 to 249. Related are 89, 67. – b_jonas 11:48, 13 November 2007 (UTC)

November 12

Seriously hurt in the news

We frequently hear in the news that somebody has been "seriously hurt", or even worse "herido muy grave" or the worst "en estado crítico" (I don't know how you would say that in English, normally somebody who is in "estado crítico" dies soon). What do those expressions mean in medicine? --Taraborn 00:35, 12 November 2007 (UTC)

See Medical conditions. These labels are used by hospitals when speaking to the press and are not used among doctors. They vary in meaning from hospital to hospital. --Milkbreath 00:49, 12 November 2007 (UTC)

Proving once again that WHAAOE. (But, dang, Milkbreath, ya beat me to it. *I* was just about to post that link!) —Steve Summit (talk) 00:56, 12 November 2007 (UTC)

Thank you, guys. --Taraborn 01:07, 12 November 2007 (UTC)

Jupiter's moon Io

Is there a certain reason Io has volcanoes? —Preceding unsigned comment added by 72.38.227.206 (talk) 00:35, 12 November 2007 (UTC)

Well, I guess the answer is only really stated clearly in the very first paragraph of Io...you couldn't be expected to find something buried that deeply! SteveBaker 01:36, 12 November 2007 (UTC)

tidal stress--( Mulligan's Wake)(t) 01:37, 12 November 2007 (UTC)

stpm trial exam question

can ketone react with chlorine?thank you —Preceding unsigned comment added by 218.208.91.249 (talk) 02:04, 12 November 2007 (UTC)

Perhaps haloform reaction may be of some help. (EhJJ) 03:11, 12 November 2007 (UTC)

"brush harder, not smarter"

my dentist told me this. what does he mean? —Preceding unsigned comment added by 172.130.26.74 (talk) 02:08, 12 November 2007 (UTC)

Why don't you ask him?

The usual exhortation is to do something smarter, not harder -- that is, to do it with more care and deliberation, and less brute force. —Steve Summit (talk) 02:16, 12 November 2007 (UTC)

As Steve has pointed out, the usual phrase is "do it smarter, not harder". In this case, your dentist may be using a play on words to imply that you are not brushing hard enough. If you're not sure, you may want to ask him. (EhJJ) 03:14, 12 November 2007 (UTC)

You might be remembering it backwards, or your dentist might have said it backwards accidentally, or your dentist might have said it backwards intentionally. There’s no way we can know which is the case; you’ll really need to ask your dentist. MrRedact 07:50, 12 November 2007 (UTC)

Bamboo nomenclature

72.50.180.145 03:54, 12 November 2007 (UTC)After reviewing your article on bamboo, I'm not sure what you call stalks of bamboo. Are they called stems? I've heard them called that before. Are they called branches? Are they called culms? which according to wikipedia- "originally referred to a stem of any type of plant". What is the appropriate scientific way to name them, because I'm confused.

A bamboo's shoot is like a tree's trunk, whereas a bamboo's stem is like a tree's branch. A culm is a stem of a monocotyledon, which bamboo is an example of. Someguy1221 05:06, 12 November 2007 (UTC)

Laxative agent in apple juice that's not in pear juice?

Here's the strange thing: I get diarrhea when drinking apple juice. Even a single glass causes discomfort, and multiple are certain to cause diarrhea (which passes quickly, however). I thought this could be oversensitivity to sorbitol, but I have no problems drinking even large amounts of pear juice, which likewise contains sorbitol. Ditto for any other fruit juice you'd care to name (though I haven't tried prune juice). I have no problem with raw apples either. It could be an additive of concentrated apple juice (I haven't tried "natural" apple juice either), but I wouldn't know which one.

Though apple juice really is the only thing giving me problems (so it's easy enough to avoid), I'm curious if anyone could guess what could cause diarrhea and is just about only found in (concentrated) apple juice -- a rare chemical or ratio of something? 82.95.254.249 07:57, 12 November 2007 (UTC)

Apples have traditionally "gone through" some people, especially if the apples are the first of the season. I suspect it may be malic acid that causes this, but I stress this is pure speculation. DuncanHill 14:24, 12 November 2007 (UTC)

Well, any hint is welcome, but I don't think it's malic acid. Tart apples are my favorite, actually, and I have no problem with other foodstuffs that contain malic acid (according to the page). 82.95.254.249 20:10, 12 November 2007 (UTC)

Pseudo-stable isotopes

For isotopes with half-lives longer than the known lifespan of the universe, such as Calcium-48, how do they determine that the isotopes aren't stable? --67.185.172.158 08:06, 12 November 2007 (UTC)

Simple: get a lot if atoms of that isotope and wait for them to decay. Remember that half-life is a statistical property: a half-life of X doesn't mean that no atoms will decay until X has passed. An unstable atom can decay at any time (which is exactly why we talk of "half-life" and not the full life).

The initial suspicion that an isotope is unstable comes from theoretical considerations, and obviously it's hard to determine the half-life for an extremely long-lived isotope with great accuracy. 212.178.108.2 10:55, 12 November 2007 (UTC)

In that case, the article cited in footnote 2 explains it. They thought it was a likely candidate (via theory) for a very rare form of decay, and then spent a lot of time watching it in a test chamber (via experiment) to see if it actually did decay in that way. And it did. Hooray. --24.147.86.187 17:00, 12 November 2007 (UTC)

A radiation counter can pick up a single atomic decay (so long as you shield it from background radiation) - if you have a mole of whatever isotope you have then you have 6x10²³ atoms. A mole is the atomic weight expressed in grams - so a mole of a solid or liquid is a pretty reasonable quantity to measure. The age of the universe is something like 4x10¹⁷ seconds - and a mole is 6x10²³ atoms - so in half the age of the universe, you'd expect 3x10²³ radioactive decay events - so you'd expect about half a million decay events per second. Easily detectable! More to the point of course, if this is a synthetic isotope (made in a nuclear reactor for example) so that it's "fresh", it'll be radiating a lot more than it will be when it's reached it's half-life. SteveBaker 18:51, 12 November 2007 (UTC)

Penguins in the Arctic? Polar bears in the Antarctic?

Just checked the articles on Penguins and Polar Bears. Just wanted some confirmation, are there any penguins that live in the Arctic? Also are there any Polar bears in the Antarctic? 64.236.121.129 14:20, 12 November 2007 (UTC)

No, and no. DuncanHill 14:22, 12 November 2007 (UTC)

But they could live there, couldn't they? I mean, if you kidnapped some and dumped them there, they'd manage ok, wouldn't they (not that I advocate kidnapping well dressed animals or anything)? Jeffpw 14:44, 12 November 2007 (UTC)

No - Penguins are almost 100% confined to the southern hemisphere (they do creep just above the equator - but not by much) - but not all species live in snow and ice - some are very happy in the tropics. Polar bears are strictly Arctic. Whether you could transplant them depends on an awful lot of things. Bears live on the mainland as well as in the arctic ocean - if you dumped them in the antarctic, they'd have no way to make it do warmer areas in the winter - also the species they are used to hunting would not be present. Some penguins have these very complicated behaviors where one sex gathers together far inland to look after the eggs while the other partner goes off for food. It's not clear how this would work in a continuously moving sea of ice floes - do penguins navigate somehow? I'd be quite surprised if relocating either species would actually work out well. SteveBaker 15:03, 12 November 2007 (UTC)

• The polar bears would probably eat the penguins. Seriously. The kind of penguins that live in Antarctica generally are unable to recognize any land animal as a predator, because the only land animals that have ever attacked them in the last million years or so have been humans or escaped domesticated animals like dogs. If you took a polar bear to the Antarctic, the polar bears would very quickly gravitate towards this huge, meaty, docile food source. If you were to transplant some penguins to the Arctic, then even if they could solve the problem of figuring out which landmass to lay their eggs on, eventually the polar bears (which will eat any kind of animal if they're hungry enough) will figure out that they're easier to catch than their usual prey, and kill them off in short order. --M@rēino 18:54, 12 November 2007 (UTC)

Well, the penguins are prey to Leopard seals and killer whales - so they have seen large predators - just not big, furry white ones. It's hard to know what their reaction might be. Certainly they are generally unafraid of humans. (True story: When my kid was about 5 years old, we went to SeaWorld, saw the Shamu show and then visited the Penguin enclosure for a behind-the-scenes tour. My son (who happened to know a lot about penguins) picked the moment with the most other people around to proudly (and loudly!) announce that "Shamu is a killer whale - he likes to eat penguins!" - the penguin-keepers were torn between their roles as "teaching kids about nature" and "being good corporate employees" - so simultaneously, one of them said "Yes, that's right!" and the other one said "No, Shamu is friendly with EVERYONE!" - then each of them realised their horrible blunder and changed their story - it took them quite a while to decide what story line was the best and lamely trot it out. It was hilarious!) SteveBaker 21:06, 12 November 2007 (UTC)

I will gladly concede that penguins face aquatic predators (and avian predators) -- just not land-based predators. --M@rēino 21:25, 12 November 2007 (UTC)

Wrinkled face

Is there an illness that makes the skin wrinkle excessively? Keria 17:04, 12 November 2007 (UTC)

There is evidence that smoking can do that to you. SteveBaker 18:39, 12 November 2007 (UTC)

I'll point out that our article on Wrinkles sucks, so this question might require some real digging. --M@rēino 18:57, 12 November 2007 (UTC)

As far as I know, wrinkling of the skin is caused by old age, however certain skin disorders may contribute to wrinkles too. Topical Corticosteroids as often used by Eczema sufferers are notorious for thinning the skin and this can definitely cause premature wrinkles. GaryReggae 22:41, 12 November 2007 (UTC)

As the piccie in Wrinkle article demonstrates, masturbation makes wrinkles a lot, lot worse. Myles325a 22:51, 12 November 2007 (UTC)

We must have a few doctors on the science desk, a dermatologist who would like to add a "disease" section on the article wrinkle? Keria 02:55, 13 November 2007 (UTC)

There is a wrinkly skin syndrome, but the description seems to indicate that the wrinkly skin is not on the face. --JWSchmidt 03:55, 13 November 2007 (UTC)

medical ebooks

i am a 2nd year mbbs student of osmania medical college.please give me information about sites to download medical ebooks,so that i can clear evrything. —Preceding unsigned comment added by 117.97.30.240 (talk) 17:13, 12 November 2007 (UTC)

You could try our sister site [Wikibooks] although I don't know if there is anything medical there. Chances are if it's anything too specialist, the best option (apart from spending extortionate amounts of money on textbooks) is a visit to your local library. GaryReggae 22:39, 12 November 2007 (UTC)

how does our organism recognize foreign tissue?

How can our organism distinguish between our own tissue and foreign ones? Of course, the DNA is different, but how our immune system can know it? —Preceding unsigned comment added by 80.58.205.37 (talk) 18:28, 12 November 2007 (UTC)

Antigens on blood cells.

Mainly due to Antigens. These are molecules on the outside of cells, and they are distinctive to each type of cell. For example, there are 2 two types of blood antigen (A and B), so someone with blood type A has "A" antigens on their blood cells. If you give these to someone else whose blood is also A (or AB), the body accepts it, while if you give it to someone of blood type B, the body can't recognise the blood antigens, so it attacks the blood, which causes all kinds of nasty effects inside the body. Laïka 18:50, 12 November 2007 (UTC)

See also, here: "To be able to destroy invaders, the immune system must first recognize them. That is, the immune system must be able to distinguish what is nonself (foreign) from what is self. The immune system can make this distinction because all cells have identification molecules on their surface. Microorganisms are recognized because they have unique, foreign identification molecules on their surface. In people, identification molecules are called human leukocyte antigens (HLA), or the major histocompatibility complex (MHC). HLA molecules are called antigens because they can provoke an immune response in another person (normally, they do not provoke an immune response in the person who has them). Each person has unique human leukocyte antigens. A cell with molecules on its surface that are not identical to those on the body's own cells is identified as being foreign. The immune system then attacks that cell. Such a cell may be a microorganism, a cell from transplanted tissue, or one of the body's cells that has been infected by an invading microorganism." Rockpocket 18:52, 12 November 2007 (UTC)

Potassium chloride and seeds

Is potassium chloride a fertilizer like potash, or a toxin like chlorine? How it will affect the growth of seeds? 199.89.180.65 18:37, 12 November 2007 (UTC)

• The majority of the potassium chloride produced is used for making fertilizer. Just remember that it might kill your livestock if they eat a bag of it. --M@rēino 19:00, 12 November 2007 (UTC)

Mobile phone buzzing

What's the buzzing/beeping that speakers make just before a mobile phone rings? I can't imagine the phone is making an electric/magnetic field strong enough to affect speakers from 3+ metres away. And if it is, is it safe to keep it near my computer? Laïka 18:45, 12 November 2007 (UTC)

Don't worry about it. My cellphone does that to the earbuds on my MP3 player and my FM clock-radio - it's simply the phone acknowledging the cell tower prior to ringing the ringer. The radio signal from the phone is plenty strong to induce a current in a wire of a suitable length to act as an antenna. It should be OK to keep it by your computer - the voltage is enough to hear on a speaker because they are analog devices - also loudspeakers and headphones have long wires leading to them that make great antennas. But no, it won't affect your computer (except that you might hear it on the computer's speakers). SteveBaker 20:55, 12 November 2007 (UTC)

Yes, this is very common although some speakers appear to be sensitive to this and others not - depending on whether the cable is shielded - otherwise the cable will act as an aerial and pick up the electromagnetic waves! It won't do any harm though, other than the obvious interuptions to your audio. GaryReggae 22:37, 12 November 2007 (UTC)

It occurs to me that there is an easier way to explain this convincingly. I should point out that inside the phone is a small computer - you know it survives the most intense radio signals the phone can put out without screwing up. What's more, radio signals decrease in strength as the square of the range. The computer in the phone is at most maybe 2cms from the radio transmitter. So if you put your phone maybe 20cms from your desktop computer, the signal strength will be 100 times less. If the computer in the phone can take the full strength, then for sure your desktop machine will be OK with just 1% as much radio interference. SteveBaker 23:42, 12 November 2007 (UTC)

Also, a desktop computer usually has a metal case (with few holes), so the electromagnetic waves most probably can't get in it. This doesn't apply to notebook computers of course. – b_jonas 11:21, 13 November 2007 (UTC)

A designer wishes to calculate the thickness of a steel cable for suspending a passenger lift

The total length of cable supporting the lift when it is at the ground floor is 8 m. The mass of the lift when full of passengers is 950 kg. The designer has decided to incorporate a safety factor of 10 into the lift cable: i.e., the cable must be able to withstand 10 times the load it will actually be exposed to in service, before it fails. The steel selected for the cable has a failure stress of 900 MN m– 2 . (a) Using this information, calculate the required diameter of the cable. Show all your working. Assume that the cable is a single piece of steel, with a circular cross-section. (Ignore any effect of the weight of the cable in your calculation.) The downward force F on the cable is calculated by multiplying the total mass m (expressed in kg) by g, the acceleration due to gravity: F = m × g Take the value of g to be 10 m s–2. (In reality there is extra force needed to accelerate the lift upwards, but as this is relatively small, there is no need to consider it here.) Hint: the safety factor means that the cable will fail – the stress will reach its failure stress – when it is loaded to 10 times the intended design load. Use this to calculate the cross-sectional area of the cable, and so its diameter. I found the diameter to be between 11 and 12 mm —Preceding unsigned comment added by Flano1 (talk • contribs) 19:09, 12 November 2007 (UTC)

So do I. 169.230.94.28 19:23, 12 November 2007 (UTC)

This does sound a bit like a homework question to me ("Show your working" is always a dead giveaway!) - please look at the top of this page where you'll see it's our policy not to help people with homework. Sorry. If there is any specific part of the math/physics you can't understand, then feel free to ask specifically about that problem and we'll be more than happy to assist. SteveBaker 20:50, 12 November 2007 (UTC)

It looks like you have all the information you need here to calculate the answer. The most obvious thing to do is ignore the factor of ten for the moment, work out the diameter of cable needed just to support the normal load then multiply it by ten. Our page on Elevators may be of use. GaryReggae 22:34, 12 November 2007 (UTC)

Erm...cough...no, no, NO! Cable strength is proportional to cross-sectional area - not diameter. To get a factor of 10 safety factor, you only need to make the cable sqrt(10) times thicker. About 3.16 times thicker should be fine. SteveBaker 00:01, 13 November 2007 (UTC)

Using the fracture strength of the cable, instead of the yield strength, sounds like a bad idea as well, particularly for applications involving lifting humans... Titoxd^{(?!? - cool stuff)} 00:13, 13 November 2007 (UTC)

Percent solutions

While interviewing undergraduates to be a lab helper, our lab manager was bemoaning how every single candidate could not explain how to make a molar solution. She then asked one how to make a 1% percent agarose solution [weight/volume] and the hapless student suggested filling a measuring cylinder to 1ml with agarose then filling it up to 100ml with water. After we were done laughing at his expense, I noted that doesn't bode well for the future of American science, as it should be simple to work that one out by logic. But this got me thinking that might not actually be the case: a percentage solution [w/v] is considered to be 1g in 100ml. But logically, it should probably be 1mg in 100ml. Are the w/v units different simply by convention, or is there a logical explanation? Rockpocket 19:16, 12 November 2007 (UTC)

In CGS (centimeter, gram, second) units, the base unit of mass is the gram, while the 'natural' unit of volume is the cubic centimeter (equal, of course, to one milliliter). So you shouldn't be deceived by the 'milli' prefix; what you should be thinking is 1% (w/v) is 1 gram in 100 cubic centimeters, which just happens to be 1 gram in 100 mL. TenOfAllTrades(talk) 19:42, 12 November 2007 (UTC)

It’s ultimately only a guess, but I don’t think the name "percentage solution" was originally perceived to be a good name for what it means due to how it works out in CGS units, but rather due to the density of water, which is by far the most common solvent. 1 ml of water weighs almost exactly 1g. (Indeed, the gram was originally defined to be the mass of 1ml of water.) So 1g of solute in a water solution that totals 100ml means that the solute comprises very close to 1% of the solution by weight (w/w). MrRedact 20:15, 12 November 2007 (UTC)

Both suggestions are perfectly logical explanations. Thanks. Rockpocket 23:52, 12 November 2007 (UTC)

Running cool water over frozen drink defrosts. Why?

Sometimes I put canned soft drinks in the freezer, but I occasionally forget about them. When I finally take them out, they're frozen solid. I found out that I can run cool water (regular temperature) from the kitchen sink over the cans, while holding them at a 45 degree angle and rotating. After a few seconds, they're completely thawed out. If I take too long, they might even be too warm to drink! How does cool running water thaw out a frozen drink in only seconds? Steohawk

The drink you remove from the freezer isn't actually frozen solid — not even close. In fact, the ice that forms is neither contiguous nor very dense, because the sugar and carbonation bubbles in the soda pop interfere with the water molecules forming a contiguous lattice. It feels as though it's frozen solid because it only takes a fairly large chunk of fairly firm slush to provide enough support for the metal can to make it feel solid. Furthermore, water that feels "cool" (or "room temperature") relative to our normal body temperature actually contains a great deal of heat. Figure the soft drink is at 32°F. If you measure the "regular temperature" water coming from your tap, you'll probably find it is between 60°F and 70°F, for a ∂T of roughly 30 to 40 Fahrenheit degrees. The metal drink tin conducts heat very efficiently and uniformly to the contents, so your not-really-very-frozen drink "thaws" in a hurry.

Also, please sign your talk page and reference desk posts properly, not by manually typing in your user name, but rather by ending your post with four tildes ~ ~ ~ ~ (but without the spaces between them). --Scheinwerfermann 20:45, 12 November 2007 (UTC)

The water is cool - but it's above freezing - hence it's warmer than the ice and can melt it. I doubt your drink was frozen solid anyway because the pressure from the liquid expansion would likely split the can. Since the freezer will tend to freeze the liquid towards the outside of the can before the inside, there may not be all that much ice to melt and it's right at the surface where the warmer (but still cool) tap water can melt it most easily. I don't see anything weird going on here. SteveBaker 20:46, 12 November 2007 (UTC)

(edit conflict - GMTA) Who knows? Are we talking about soda (pop) like Coke? A few guesses: The can isn't really frozen solid, it just has a coat of ice all over the inner surface that makes it feel solid. When the water in the drink starts to freeze, it will freeze from the outside in because the heat is being lost through the can, and from the bottom up because of convection. As ice forms, the remaining solution will get more and more concentrated, depressing its freezing point more and more and helping it stay liquid. Running water is terrific at transferring heat, and if it's at all warmer than the can it will transfer heat to it. Do this: next time, take one of your cans outside and saw it in half with a big serrated knife (or get your mom or dad to do it). See if it is really frozen solid. --Milkbreath 20:58, 12 November 2007 (UTC)

Make sure to set up a video camera on a tripod and post the video to YouTube when you're done. It could easily be right up there with Diet Coke and Mentos!  :-) SteveBaker 21:38, 12 November 2007 (UTC)

Thanks for the answers.

BTW, I did sign my last entry with four tildes (no spaces), but it got "converted" when I saved the page. Let me try it again. Steohawk 22:08, 12 November 2007 (UTC)

Yup, that time your signature worked. I'll add that if you are eager to see inside an aluminum pop can, the easiest and safest way to remove the lid is to turn an ordinary can opener (preferably a gear-drive Swing-a-way type) 90° so its wheels are horizontal rather than vertical, clamp the rim of the pop can between the cutter wheels, and turn the can opener's handle to remove the lid and part of the rim. Be careful, for this will create a sharp edge. However, it will not create metallic dust or other contaminants (as the hacksaw method would), so you won't spoil the contents of the can. --Scheinwerfermann 23:02, 12 November 2007 (UTC)

Melted ice contains white particles, even purified water.

Whenever I freeze water and melt it, white particles can be seen floating around in the water. They're never visible prior to freezing. I thought that this might have been caused by some impurity in the water from my faucet, so I froze water from my neighbor's purifier. After melting it, the same white particles were visible. They're even visible in hot water, so I know that they aren't tiny bits of left-over ice. What are these particles and why do they only show up after melting ice? Steohawk 22:14, 12 November 2007 (UTC)

Make sure that the container in which you make your ice is clean and not shedding dust or other bits of material and that you cover it with something similarly clean when you're freezing/melting it. Maybe put the water in a zipper bag during the freeze and thaw? My older plastic ice-cube trays used to flake off over time, and also the paint and other coatings in the freezer itself did. DMacks 22:29, 12 November 2007 (UTC)

Possibilities. 1. Your neighbour’s purifier is full of gunk 2. Your freezer is full of gunk 3. The container you are using is full of gunk 4. The back of your retinas are full of gunk. Myles325a 22:30, 12 November 2007 (UTC)

Is it possible that you live in a 'hard water' area? I could maybe imagine there being a lot of dissolved minerals in the water that could maybe come out of solution when you freeze the water - making these little particles. What we need here is an experiment. (Woohoo! Actual science on the science desk!) The way to prove whether I'm right is to filter the water you get by melting the ice cubes and then re-freeze it in the same freezer/ice-tray that you used the first time. If you melt it again and it has particles in it the second time around then the bits must have come from the freezer/ice-tray. If there are no particles the second time around then DMacks & Myles are wrong and I guessed right. As an alternative experiment, you could try washing your hands with a little soap and the melt-water (wait for it to get to room temperature first) and see if you get lots more lather than you do with tap-water. Soft water produces more bubbles from soap than hard water and if I'm right and you somehow removed minerals by freezing and filtering - then you'd expect to get more lather with the melt-water. SteveBaker 23:57, 12 November 2007 (UTC)

E = mc2 - how does c relate to the weight and energy units?

Everyone can see why there is so much energy in a given mass, because c, the speed of light is so large, and c2 is enormous. But why couldn’t we just define c as a single unit? How does Einstein define a measure of speed with weights and energy values?

After all, c = sqr(E/m). I have often thought about this, tho obviously I am a layperson in physics, and my brain hurts. Myles325a 22:25, 12 November 2007 (UTC)

We actually have a page about the E=mc2 formula, with some info. One hand-waving reason that "c² is more reasonable than c" here is that we need the units of measurement (dimensional analysis) to fit. A conversion factor for an energy/mass equivalence must be expressed in terms of distance²/time²). Once you have the relationship though, you can do algebra and other manipulations to express t he equation in different forms. Saying "c = sqr(E/m)" is not ideal because it fails if m=0. DMacks 22:37, 12 November 2007 (UTC)

In SI units, mass is in kg, lightspeed is in meters per second and energy is in Joules - which is SI shorthand for: "kilogram meters-squared per second per second" ...which is a bit of a mouthful.

You can work in any scale units you like so long as you are consistent. If you want to define your unit of length as (say) the distance light travels in a second (a "lightsecond") instead of the more usual 'meter' that's OK. The E=mc² equation still works - except that now we've defined c to be 1.0, instead of the result 'E' being in Joules (which is shorthand for kg.m².s^-2) the answer would be in some new unit of energy because we defined our unit of length to be a lightsecond instead of the meter. Let's name it after it's creator and call it the 'Myle'. The Myle is shorthand for kg.lightsecond².s^-2. One kilogram of matter would contain exactly one Myle of energy...very convenient! But the Myle would be a truly phenomenal amount of energy because it's in units that contain lightseconds²!! The Myle simply isn't a very useful energy unit. A 'AA' battery stores about one kJ - but and inconvenient 0.09 attoMyles! On the other hand, you could instead define your time unit as the time light takes to travel in one meter - c is still equal to 1.0 but your unit of time is microscopic - so your unit of energy is still enormous. You can shuffle the unit definitions around however you like - but the result is the same. Dimensional analysis is always very instructive in these cases. SteveBaker 23:31, 12 November 2007 (UTC)

It's also worth noting that when working with problems in relativity, velocities are generally expressed as fractions of c rather than using more common measurements. Donald Hosek 02:00, 13 November 2007 (UTC)

November 13

Technology and Depression

Does the more engrossing technology becomes translate to the more depression society feels as a whole? (Forgive the grammar.)

Living in our parent's house, no post-secondary education or real job experience between us, my brother and I were absolutely entranced with World of Warcraft. "Real" decisions with all their complications were so far removed from the crisply cut and dry work/rewards system in game. I alone spent 7 months of 16-hour grueling days rising to the rank of Grand Marshal of the Alliance and I loved it. We lived every waking hour in WOW for 2 years. Our parents eventually gave us an eye-opening ultimatum and he killed himself with a plastic bag and duct tape about a year ago. I was in a psych unit for about 2 months after. I know now what horror and true self-loathing feel like.

In my heart I know this is a sign of things to come for society as a whole. I'd like to know if depression and technology are correlated. Sappysap 02:13, 13 November 2007 (UTC)

There are arguments that they are, but I don't believe so. Depression is fairly clearly genetic, and has existed in some form for all of history. Suicide, of course, being the worst-case fate of depression, has also been in existence and I don't believe suicide rates have increased or decreased significantly with time, though certainly environmental factors have played a role. I have no significant sources with which to back this, though, other than the fact that "melancholy" was a diagnosis since at least the early 17th century. SamuelRiv 03:14, 13 November 2007 (UTC)

Reduction of Fe(III) in FeCl₃(aq) to Fe(II)

How would I reduce the iron in FeCl₃(aq) to Fe(II) in order to use the indicator ferrozine, which only detects Fe(II), not Fe(III)? Can I somehow use ascorbic acid to do so? What would the chemical reaction be? Could this be undergone by using titration? Chickenflicker-♣ 02:48, 13 November 2007 (UTC)

Edit: What would the reaction between Hydrazine (N₂H₂(l)) and FeCl₃(aq) look like? Chickenflicker-♣ 03:03, 13 November 2007 (UTC)

horizontal component of speed

This is a mix between a maths and physics questions...anyway here goes:

An object is being pulled up a slope by a force at a constant speed of say 3m/s. At the top of the slope is a horizontal plane. What is the object's speed at the beginning of its journey along the horizontal plane? Is it 3m/s, or is it just the horizontal component of velocity (ie. 3cos(angle))? Is the vertical component of velocity wiped off or does it become a part of the horizontal velocity?

    ->>______________________
   -  /
  -  /
    /
   /
  /
 /
/

What about when a ball rolls down a slope and then travels along flat ground? At the beginning of its journey along the flat ground, is its speed just the horizontal component of its previous velocity or is the magnitude of both components of its previous velocity?

                     /
                    /
                   /
                  /
                 /
                /
____________<<-/  

Thanks! D3av 02:53, 13 November 2007 (UTC)

In these types of problems you usually approximate the sharp corner as a tiny rounded corner. Then assuming ideal conditions the ball rolling down the hill will conserve kinetic energy when it hits flat ground. The ball being pulled up a hill will also conserve kinetic energy, but the end result depends on the precise wording of the problem. If you are constrained to be on the surface of the slope, then you move forward with kinetic energy conserved. However, if unconstrained, you fly upwards as a projectile with some initial velocity at some angle. SamuelRiv 03:09, 13 November 2007 (UTC)

So say the one moving down the hill is unconstrained (just freely rolling down). Would you use the horizontal component of velocity or the whole thing?

When you say "with kinetic energy conserved", does that mean that the vertical component of velocity becomes part of the horizontal component?

We had one question in which the object seemed to be constrained as it was being dragged up the slope. The instruction was to use only the horizontal component of velocity when it reached the horizontal plane at the top. Was this a correct instruction? thanks. D3av 03:26, 13 November 2007 (UTC)

As SamuelRiv said, it depends on the precise wording of the problem, in particular how the force is being applied. For example, if there's something pushing on the object from the left (slowly, so that gravity keeps the object from ever leaving the surface), moving at a constant rate to the right,

       ______________________
      /
->|  /
->|*/
->|/
  /
 /
/

then the horizontal component of the velocity will remain constant, and the vertical component will go to zero at the corner. If there's a rope attached to the object that goes up and over the corner (so the corner acts somewhat like a pulley), and the rope is being pulled at a constant rate,

       ______________________->
      /______________________
     //
    //
   */
   /
  /
 /
/

then the component of the velocity parallel to the rope will remain constant, so the horizontal and vertical components will change as the rope's direction changes. If there's something pushing the object in the direction parallel to the slope,

       ______________________
\     /
 \   /
  \*/
   /
  /
 /
/

(...well, I don't know how to make it look like that thing is moving diagonally upwards with ASCII, but anyway) it will actually move faster when it reaches the horizontal surface because the component of the velocity in the direction of the slope will remain constant, but it gets a new perpendicular component when it passes the corner. So it all depends which of these different problems you're trying to answer. —Keenan Pepper 06:27, 13 November 2007 (UTC)

The vertical component won't magically go to zero, regardless of whether the object is being pushed or pulled. Unless the object is held on some sort of track, it will rise into the air above the horizontal plane until gravity brings it back down. Clarityfiend 08:00, 13 November 2007 (UTC)

Thankyou very much for those answers. They are very comprehensive and clear. I'm still unsure though (as I wrote above) about what will happen to a ball that is rolling down a slope and then continues along a flat surface. (The only forces acting on it are the force of gravity and the normal). Thanks D3av 09:45, 13 November 2007 (UTC)

It depends on the nature of the ball. When the ball hits the bottom of the slope, there is a collision. What happens next depends on what the ball and the ground are made out of. A softer ball might bounce a few times - eventually rolling off along the new direction at roughly the speed it was moving down the slope - much conserving kinetic energy (assuming we ignore losses). What happened was that the kinetic energy temporarily turned into elastic energy from the compression of the ball's material - then that elastic energy was turned back into kinetic energy directed in a different direction. That little energy interchange permitted the velocity vector to change but the kinetic energy to be conserved. A harder ball might simply give up the vertical component of its energy in the collision (so the kinetic energy turns to heat) - continuing to move along the horizontal region at a speed equal to the horizontal component of it's former motion. Without more information, you can't say which it will be.

When the ball is travelling up the slope, the same thing happens. At the top of the slope the ball will continue upwards (because of conservation of momentum) - travel on a free parabolic trajectory and eventually collide with the top of the slope. Once again, the ball will either bounce - causing it's new velocity to be horizontal - with the same speed as it was travelling up the slope - or it'll impact without a bounce - causing it to lose the vertical component of it's former velocity.

With real balls, the behavior is somewhere between the two cases - energy is lost in the bouncing and the actual horizontal speed will be a blend between the old horizontal speed and the old net speed.

SteveBaker 12:26, 13 November 2007 (UTC)

stars come down

hi my question: there is a place in space that stars come down(and it is a holy place...god says in quran)Have you heard anything about it? —Preceding unsigned comment added by 213.207.252.64 (talk) 10:20, 13 November 2007 (UTC)

Could you provide a reference to a specific passage in the Quran? Scripture often contains sections that need to be read very carefully to determine what they refer to exactly. My first guess would be a black hole. (EhJJ) 11:41, 13 November 2007 (UTC)

It's possible that the book refers to meteorites as stars. -- JSBillings 11:43, 13 November 2007 (UTC)

If "come down" means "move deeper into a gravity well", then I suppose you could say that "stars come down" as they fall into a supermassive black hole. Those are found at the centers of many (and perhaps all) galaxies. But there is no one, single place where this happens in the universe - it's likely that there are at least as many of these objects as there are galaxies - and there are billions of those. The nearest one of these things is at the center of our own Milky Way galaxy.

I find it amusing that a black hole might be considered a holy place. Good and useful things (like stars and planets) go in - nothing (including light or information) comes out! But really, any sufficiently vague and ancient statement (with likely translation errors and a wide laxity of interpretation) can be made to fit some real thing. I don't think I'd read anything into this statement beyond that whoever wrote it didn't know what a star really was and thought that the idea of the seemingly immutable stars 'falling' was a dramatic image. Spotting an occasional meteor and (incorrectly) assuming that was a 'falling star' might serve to reinforce that. Sadly, with what we now know, it really doesn't make any sense.

SteveBaker 12:07, 13 November 2007 (UTC)

What snake a specific book refered to

I'm looking for a king of snake who may havg from a tree over the Amazon river or one of its tributaries, would look like a vine to someone in a canoo going under that tree, and can swim away if grabbed off the tree. I looked in Category:Reptiles of South America, but couldn't find it - the Emerald tree boa looked promissing, but I couldn't find evidence of it being able to swim. Od Mishehu 11:29, 13 November 2007 (UTC)

Perhaps an anaconda? (EhJJ) 11:38, 13 November 2007 (UTC)

I don't think it hangs from trees. In the book in question (Magic Tree House book called Afternoon on the Amazon), Jack tries to get to the river bank by pulling on a "vine" that turns out to be a snake. Od Mishehu 11:47, 13 November 2007 (UTC)

I'm afraid I don't understand the question. It was a fictional snake. --Milkbreath 12:01, 13 November 2007 (UTC)

Condensation and Deposition

I need to measure the rate at which Condensation and Deposition (physics) occurs at standard temperature and pressure from a particular inorganic vapor with a melting point in the 1000s K produced by combustion. I have had no luck so far. How do physicists and chemists measure condensation and deposition? As a biologist without a whole lot of physical chemistry, I haven't even been able to figure out where to begin. I am hoping that there is a formula but I fear that these rates are determined only empirically. Thanks for any help. Spc303 12:59, 13 November 2007 (UTC)