Wikipedia:Reference desk/Archives/Science/2008 July 25

Science desk
< July 24	<< Jun | July | Aug >>	July 26 >

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

July 25

Intellegent design...

Just looking at the human body alone, how much of it has evolved and how much was designed?I'm assuming the more complex organs like the eye and the brain were designed, and simpler ones like finger nails and the nose evolved naturally.... but I just dont get how a simple life form can have coplex organs like the aforementioned eye before the foot has had the time to evolve, or is it a case that an organism evolves to a certain level and then carefully designed components are added at different stages... I'm probably missing something obvious but your help would be appriciated, :)165.228.176.26 (talk) 06:49, 25 July 2008 (UTC)

As far as I can tell, you're the first to come up with the idea that some components are evolved and others designed. I think everyone else pretty much says either it's all evolved, or all designed. The empirical evidence supports the former view, with the latter simply being a strongly-held religious belief. - Nunh-huh 06:56, 25 July 2008 (UTC)

Well, fish have eyes (What do you call a fish with no eyes? a fsh), but they haven't evolved feet. Current consensus on the Timeline of evolution has it that animals in general have been around for much much longer than those with mammal-like feet. You don't exactly start from nothing and try to achieve feet and eyes at the same time.

Even if the eye couldn't evolve in the time for feet to evolve, would that matter? You would have blind things walking around for a while, while eyes gradually evolved. (N.B. This is not how it happened)

You might be interested in evolution of the eye, which explains how such a complex organ could evolve. The short answer is "from simpler ones", and this applies to all of the other organs too. AlmostReadytoFly (talk) 08:21, 25 July 2008 (UTC)

The problem of how the eye could develop through evolution is debated and explained by many evolutionary biologists, so there should be several texts on this online in addition to wikipedia, if you'r interested. The basic approach is to show that each step towards an eye increases evolutionary fitness. then one document through fossils or contemporary simple organisms that the intermediate steps indeed happened.

For instance, just being able to distinguish light from dark or the general direction of light would be an advantage for an organism and is indeed found in many of today's microscopic creatures.

As an apropos, Nunh-huh is wrong to say that you'r alone with the evolution+creation idea. Some creationists accept evolution-like phenomena within a species but denies that new species are ever created from old ones. EverGreg (talk) 08:30, 25 July 2008 (UTC)

Of course, that's not at all what I said. -Nunh-huh 09:17, 25 July 2008 (UTC)

Just greated an acount:) I was just using the foot as an example of something of a body part simple enough as to not necessatate design... I'll try to rephrase the question, basically I understand that parts of us evolve naturally but other parts are for to complex not to have had a designer, I'm just wondering at what stage the designed components were added? For example, back when we were just a basic blob of flesh eyes wouldn't have been much use without a brain to process the information, they would have been largely pointlessHypervalve (talk) 08:45, 25 July 2008 (UTC)

Well, first of all, a foot is a pretty complex body part. You've got circulation that brings in oxygen to the muscles, you've got the muscles themselves which make it move, you've got bones that support the foot (and the rest of the body) and cartilage that ties them together and allows them to move, you've got tendon that connects the muscles to the bones, you've got (in the cases of humans and many other, but not all species) toes that help with balancing yourself, you've got a lot of useful nerve endings that help you feel your way when you're barefoot, you've got skin that keeps out germs and regulates your body temperature by sweating... I mean, there's a lot of stuff down there that works together. It's not at all "simple". An eye does a lot of cool stuff too, but they're not that different in terms of complexity. It's not as if some simple organism in the primordial slime suddenly grew up, noticed that it had feet and then started walking around on land (presumably bumping into things a lot if it didn't have eyes yet). It doesn't work that way.

Secondly, I don't think we know exactly at what stage the various components were "added". We weren't around to observe, after all, though we can certainly make some educated guesses. You should bear in mind, though, that none of this happened overnight, and a lot of it happened "simultaneously", if you can use such a term when discussing events that took millions and millions of years. -- Captain Disdain (talk) 09:11, 25 July 2008 (UTC)

I'd recommend perusal of Evolutionary developmental biology, not just evolution. A very enlightening book 'Endless forms most beautiful' is referenced there. You'll be lead to understand homeoboxes, why they are important for development of limbs etc. and how and when they evolved (which can be measured exactly). None of these facts can be explained by intelligent design. --Ayacop (talk) 09:13, 25 July 2008 (UTC)

Is it the same as saying the body is a self-designing organism? Julia Rossi (talk) 09:38, 25 July 2008 (UTC)

As the body is 'just' the means of the DNA to survive, I'd rather say 'the DNA designs itself and the body to cope with and survive in the changing environment'. However, the process is influenced by random events (changing environment, mutation), and if you want to see this, too, as design, then there is no single design but the two mentioned, survival and chance (the latter of which you may want to connect to a god of your liking). --Ayacop (talk) 09:58, 25 July 2008 (UTC)

Hi, you wrote: "basically I understand that parts of us evolve naturally but other parts are for to complex not to have had a designer", which is based on the idea of irreducible complexity. This idea is not one which is accepted by most scientists working in the field of evolution. They would probably state "All parts of us evolved and continue to evolve naturally". AlmostReadytoFly (talk) 09:48, 25 July 2008 (UTC)

Evolving anatomical structures such as eyes, brains and feet is child's play compared to the biochemical processes such as the metabolic pathways, DNA replication and photosynthesis. The first half of the timeline of evolution is taken up with evolving these well adapted fundamental mechanisms. This is where the true complexity and wonder of life lies - compared to these processes, eyes, brains and feet are just the blinkenlights. Gandalf61 (talk) 09:42, 25 July 2008 (UTC)

Hi, you wrote: "parts are far too complex not to have had a designer", which leaves you with 3 choices for how such a designer was created:

1. He evolved from simpler forms
2. Another designer designed him
3. He's always been here

I suspect you might choose #3, but if you can accept that, why not just accept the simpler idea that eyes and feet have always been here? That's certainly more believable, since we can at least all agree that they're here now. --Sean 12:59, 25 July 2008 (UTC)

As has been pointed out above, all parts of the human body, and every living organism, has evolved, and has not been "designed" in any way or part. A good introduction to this topic if you're happy to read a book is The Blind Watchmaker which explains how the eye may have piecemeal evolved. The book may be tainted in your eyes by the author "coming out" as an atheist and practically starting the neo-atheist movement, but long before all that happened, and still, this book was considered a great neo-darwinistic introduction to evolutionary thinking. —Pengo 12:29, 26 July 2008 (UTC)

Evolution of dogs

Since many dog owners prefer dogs that react to them, including when they talk to their pets, or dogs that are more intelligent than their peers, is it too crazy to suppose than someday dogs will evolve into speaking beings?Mr.K. (talk) 08:45, 25 July 2008 (UTC)

Of course not -- provided that when you say "some day" you mean that you'd be willing to wait millions of years. (I'm sure you could shave some time off that figure by aggressively breeding for intelligence, which of course didn't happen to humans in nature.) There's no reason to believe that they couldn't evolve that way. Then again, that doesn't mean that they necessarily would. Intelligence is by no means a guaranteed result of evolution. But is it too crazy to think it might happen? Nah. (Oh, and speaking would also require some considerable changes in the shapes of their mouths, of course, but what the hell, that wouldn't be impossible either.) -- Captain Disdain (talk) 08:56, 25 July 2008 (UTC)

What about greyhounds? Since they're aggressively bred for speed is it reasonable to assume that on a long enough time line the would be able to travel at a rate approaching the speed of light? Hypervalve (talk) 09:00, 25 July 2008 (UTC)

Traveling at a rate approaching the speed of light is not possible on earth. Speaking mammals, on the other hand, do exit. Mr.K. (talk) 09:22, 25 July 2008 (UTC)

...but "thinking mammals" is an open-ended research problem ;-) --Stephan Schulz (talk)

Excuse me while I pull myself together after taking that the dogs are more intelligent that the owners' peers, but dogs do speak -- it's that we can't understand them. The question of whether they learn sign language like lab chimps, or articulate verbally so they sound like Prince Charles is another issue... I personally haven't learned to do either. Julia Rossi (talk) 09:30, 25 July 2008 (UTC)

Uh, no. No. There are all sorts of problems here. If we did have a super-evolved and super-fast greyhound that could go that fast, it would need tremendous amounts of energy in order to reach and maintain such a speed... and I don't mean an extra helping of Alpo, either. The dog would also pretty much explode right away; at speeds like that, hitting the atmosphere would be like hitting a wall. The dog would be a spectacular ball of fire that would cause horrible destruction. The sonic booms, from breaking the sound barrier, alone would wreak havoc. At those speeds, the kinetic energy from each paw hitting the ground alone would destroy both the dog and the ground. I mean, overall, the energies involved in something like that would be utterly ridiculous. (Let me put it this way: a Greyhound jumping up and running full tilt to the door to do some energetic barking when the doorbell rings would make Hiroshima look like a walk in the park...) -- Captain Disdain (talk) 09:39, 25 July 2008 (UTC)

So, if we scale things back a bit - would breeding a greyhound or whippet that could run faster than the speed of sound be in any way feasible in the extreme long term? --Kurt Shaped Box (talk) 09:57, 25 July 2008 (UTC)

Well -- if you'll allow me to wax pedantic for a moment -- in that case you wouldn't scale things back a bit, you would scale things back a lot. It's comparable the difference between a single drop of water and the Atlantic, kinda. But to answer the question... uh, I dunno. I don't think so. I can think of all sorts of problems with that, one of the key ones being the greyhound's method of propulsion -- that is to say, running. Running isn't terribly efficient at high speeds. A supersonic jet fighter has a jet engine, which doesn't require any friction with the ground; it just sucks in air and spits it out. Running, on the other hand, does; the dog needs to constantly be able to hit the ground with its legs in order to maintain or increase speed. There comes a point where it's no longer a question of whether the dog can move its legs fast enough, but whether any such movement is enough to counter air resistance instead of, say, just propelling the dog into the air. (This would be comparable to what can happen to high-powered F1 boats, for example.) I guess, if the dog were to evolve some kind of claws or something that could grab the ground and keep it anchored, that would help. Also, the mechanical stress of pumping its legs that fast would be tremendous; I think more likely than not, it'd start damaging itself pretty quickly, if not immediately. And, of course, that air resistance is no joke at those speeds: pushing through the sound barrier can be pretty harsh on the body. But, you know, given enough time? I guess a dog might -- I don't really believe this could happen, you understand, but hypothetically speaking, might -- evolve muscles and joints and bone and the claws and whatnot that could somehow support this sort of activity so the animal wouldn't just shake itself apart. (The paws would take an incredible beating. Each step would send a powerful physical shock through the animal's body; I'd guess it'd get a series of concussions when running. And the physical stress directed at an object moving that fast through the air is tremendous anyway. Falling in mid-run would be like being pummeled by fifty sledgehammers... but, you know, for the sake of argument, let's assume that somehow this amazing dog can take all this.)

But even then, there's the question of energy for this kind of activity: that dog would have to have an incredibly efficient metabolism. Kibbles and bits wouldn't do the trick; it'd be burning some serious calories at those speeds, tens of thousands of them at the very least, so it would have to eat something that contained pretty serious energy -- I don't think there would be nothing in nature to fulfill that need. (And it couldn't just make up for it by having a large stomach and eating more; it'd be crucial for the dog to be as streamlined as possible.) I mean, I guess it could have some sort of a hyper metabolism and the ability to effectively store energy for future use and depend entirely on some sort of human-created ridiculously high-energy meals, but... also, the dog would have to breathe, which is just about impossible at those speeds, and in any case the demand for oxygen would be incredible when the body is working that hard, much greater than lungs could be expected to efficiently provide, and...

...nah. I really don't think so. -- Captain Disdain (talk) 10:52, 25 July 2008 (UTC)

Man. That was a good answer. :) --Kurt Shaped Box (talk) 23:24, 25 July 2008 (UTC)

I'd expect the max speed a highly evolved dog could reach to be on order with that of a highly evolved cat, namely the cheetah, which reaches 75 mph/120 kph. That's only around a tenth of the speed of sound, however. As for intelligence, I see no inherent reason why dogs couldn't eventually evolve the same intelligence and talking abilities as people, but we are talking millions of years here, even with selective breeding, as entirly new structures (like vocal cords) need to develop. Its not just a matter of varying the size and shape of the existing range of structures, which is all dog breeding so far has accomplished. However, we might be able to speed this up using recombinant DNA technology, and end up with The Island of Dr. Moreau. StuRat (talk) 16:01, 25 July 2008 (UTC)

It's not just that, it's unlikely we're even trying to make talking dogs, whatever features are being selected for it's unlikely to be those which could eventually lead to vocal chords capable of human like speech Nil Einne (talk) 17:33, 25 July 2008 (UTC)

A highly evolved dog (millions of years of successful adaptation) named Laika achieved earth orbit in 1957. Does that count as "faster than the speed of sound?" Or did you mean "without human intervention?" A dog which went over a cliff under its own power might also exceed the hypothesized 75 mph, especially if it adopted a streamlined Underdog flight posture during the fall. Edison (talk) 16:27, 25 July 2008 (UTC)

Well, going by this logic, you might put a small radio in the dog's mouth and claim that it talks, but it's pretty obvious that it's really got nothing to do with the dog's evolution. =) -- Captain Disdain (talk) 18:50, 25 July 2008 (UTC)

Yes. Dogs may some day evolve speech. But it seems unlikely to happen in our life time, if at all. While there is evolutionary pressure for dogs to be able to communicate with humans, the type of communication will likely stay non-grammatical (you could argue that there is already 'verbal' communication between humans and dogs). What has happened already is that dogs have become very good at reading human emotions and faces -- better so than even chimps (our closest relatives in the animal world). What will happen in the future is always speculation of course -- but if dogs do start to talk, will they still want to be mere pets? —Pengo 12:38, 26 July 2008 (UTC)

Good question. When I had two dogs, I was their slave (play, walk me, feed me, let me in, let me out, wash, dry... you-know-the-routine). Where is it says that dogs could talk but their vocal chords are not the right length? Julia Rossi (talk) 04:46, 28 July 2008 (UTC)

Captain Disdain said "nah. I really don't think so." I would have imagined that if the only criteria for selection is speed.... wouldn't it keep increasing incementaly... couldn't alot the constraints you've mentioned be eventually overcome if the fastest and fastest alone are always the most successful, could it really reach a point where the greyhound reaches its top average speed and cannot possibly improve? I mean there are many obvious restraints but hasn't nature come up with some pretty cool stuff in the past? 203.59.254.122 (talk) 14:21, 28 July 2008 (UTC)

Nature has absolutely come up with plenty of amazingly cool stuff in the past, but you need to understand that there are certain limitations here, most of which are imposed by the laws of physics. There are a lot of problems with this thing, but let's concentrate on what may be the most obvious, and is probably the most dramatic of them: the physical stresses involved. That thing about the dog falling down in mid-run? Even if the dog was made of steel, it would pretty much spread itself a pretty long stretch of terrain if it fell down at supersonic speeds. I mentioned "fifty sledgehammers" earlier, but that was probably a serious understatement. The kinetic energies involved in having a 30 kg dog impact with the ground at supersonic speeds are pretty awesome. It follows from this that just the dog running, with its paws hitting the ground, would do pretty incredible damage. It'd be like a machine gun hitting the ground with every step -- only much, much more destructive. Let's take, as a point of comparison, a M240 machine gun, which is a pretty modern weapon.

Consider the following: the speed of sound is around 1235 kilometers per hour, or 343 meters per second. The M240's bullets are a lot faster than that; they are fired at a speed of about 905 meters per second, or almost three times the speed of sound. But these bullets are are very light, 146 grams. The greyhound is over 200 times heavier than that, and it's got four paws that are constantly hitting the ground at speeds considerably faster than the speed of sound (after all, the individual feet need to move very fast in order to push the heavy dog forward at that speed). This translates to pretty incredible forces; the dog would have to expend... uh, let's just say humongous amounts of energy to reach and maintain the speed of sound. This means the dog's feet could shatter concrete and destroy steel structures with ease, just like bullets -- only these would be much bigger and heavier "bullets", much closer to artillery than gunfire in effect, I think.

But here's the thing: if you fire a machine gun at a wall, you'll probably perforate the wall, but the bullets don't remain intact. They tend to get torn apart by the forces involved. The dog's paws would also be subjected to comparable forces, because each action must have an opposite and equal reaction, as Newton's third law decrees. That means the dog's paws would have to be bulletproof -- and I don't mean they would have to be strong enough to take a bullet or two, I mean they would have to be strong enough to withstand constant and sustained machine gun fire, pretty much. The idea that it could just "evolve" to a point where this wouldn't be a problem is funky, but it doesn't fly. Evolution is pretty amazing, but it's also got pretty obvious limitations. And in any case, even if the dog somehow could evolve into something that's strong enough, capable of maneuvering at those speeds and possessed of a some kind of natural shock absorbers, the energy requirements alone would make it all but impossible. -- Captain Disdain (talk) 04:12, 29 July 2008 (UTC)

Captain Disdain, aren't you assuming that as the dog evolves the basic blueprint remains the same, with the rate of motion of the paws increasing drastically up to achieve these high speeds- the rest of the dogs body being renforced so as to withstand the stresses involved.... obviously these constraints exist the way the dog is designed at the moment, but if it was to realistically move at supersonic speeds- a new method of propulsion is required, the way the dog produces energy needs to change drastically etc etc, over millions of years of selection for speed I assume the result would look absolutely nothing like a greyhound as we know it... I'll admit I'm far from an expert on evolution and the physics involved- but if its possible for a mass, e.g. a bullet, to travel at the speed of sound couldn't nature achieve the same thing with a living organism? 165.228.176.26 (talk) 08:44, 29 July 2008 (UTC)

Sure, I'm assuming all sorts of things. Hell, could be the thing goes and evolves wings and some sort of a biological jet engine. Or just wheels. (Although the question was, "would breeding a greyhound or whippet that could run faster than the speed of sound be in any way feasible in the extreme long term?" But anyway.) But even if we were to assume that this could happen -- and I'm extremely skeptical about that -- that wouldn't change the fact that the basic energy requirements would be pretty ridiculous. Just because we can make something move at or past the speed of sound, it doesn't follow that something can naturally evolve to do that. I mean, it's possible for a mass to travel at relativistic speeds, too, but that doesn't mean something living can propel itself that fast by some means.

I mean, in theory, I suppose the dog could evolve to have a hyperefficient metabolism, a way to store enough energy to ensure that the animal doesn't starve to death after a single sprint (and bear in mind that the way animals store energy is by getting fat, which isn't a very fast process), incredible shock absorbers, skin, bones and muscles that are much more durable and impact-resistant than any rock (and yet pliable enough to, y'know, move), a respiratory system that can provide enough oxygen and expel carbon dioxide, the sensory abilities and the reflexes that enable to animal to sense where it is going and to make necessary maneuvers (bear in mind that a human being could never navigate at ground speeds like that; you'd hit something before you really even saw it coming -- and just making a turn at those speeds would be very difficult, what with the torque and g-forces involved), and probably a hundred other things that are equally unlikely. (And when I say "in theory", I'm probably giving this thing the benefit of the doubt in all sorts of possibly impossible ways.) But that's so far removed from reality that you might as well say that in theory every baby born in 2009 could be a girl. Ain't happening. -- Captain Disdain (talk) 10:58, 29 July 2008 (UTC)

The mechanics of graden furniture (AKA "garden furniture")

I'm visiting my folks at their summer-place this week, and me and my dad (well, mostly him, I'm basically the muscle of this operation) are making a large table for the garden out of concrete. It's going to be a slab that's 220cm x 90cm big, resting on three pillars in an isoceles triangle, with two pillars at the corners on one of the 90cm side and the other about 120 cm's into the table (see diagram). The slab weighs about 182 kg. This design is for two reasons, the first being that it is going to make the slab very stable. If there was four pillars and one was slightly shorter, the table might wobble depending on where the weight is (the slab is just going to be laid on top of the pillars, not screwed to it or anything). Second, my father wants to acheieve an effect that makes it appear like the table is "floating". I had some doubts about this design, mostly because I figured that if you put enough weight on one of the corners, the hole thing would flip over and fall off. To back up my assertion, I wanted to calculate how much weight would make the table flip over. And that's where I need you guys' help :)

Here's a diagram of the table, on a coordinate system with (0,0) at the bottom left corner of the table. The green squares are the pillars (which are 10cm x 10cm).

So, here's the problem: how much weight can you put on the bottom right corner (at (220,0), in other words) before the whole table flips over? I'm not really very good at this, but I tried calculating it and I got about 35 kgs (which, if true, is far to little, and I'll have to dig up one of the pillars and move it :( ). I would really appriciate if I could get someone to verify that I'm using the right method and that my calculations are correct.

The way I did it was to figure the table as just one big lever, with the red line as the fulcrum. Then I used the lever principle to figure out how much each part of the table pushes down, and how much force at the bottom right corner would make that side "heavier". The red line meets the edge of the table at approximately (0,0) and (220,65). I figured out the center of gravity for both parts of the table, which I got to be (89,58) and (149,22). To get the distance between the centers of gravity and the fulcrum-line, I used this neat formula. The distances are about 30cm and 20cm respectively (30.16 and 20.36 to be specific). The product between the distance and the weight (in newtons) of the top part of the table is 34050.64 Nm and the bottom part is 12989.68 Nm, according to my calculations (this is where the lever principle comes in). That means that the top part is 21060.96 Nm "heavier" than the bottom part. Since the distance from the bottom right corner to the red line is 62.2cm (again, using the formula mentioned above), to flip the table over it, you would have to apply 21060.96/62.2 = 338.6 newtons of force, or about 35 kilogram in earth gravity.

As I said, I really just want someone to tell me that this is the right way to do it. If someone could check on the actual calculations, I'd be hugely grateful, but that isn't necessary. Just a confirmation of the method would make me a very grateful man. Or not so much, if I have to spend most of the afternoon digging the damn thing up :) ADFSGL (talk) 11:28, 25 July 2008 (UTC)

Small correction: replace all occurances of Nm with Newton-centimetres :) —Preceding unsigned comment added by ADFSGL (talk • contribs) 12:11, 25 July 2008 (UTC)

I can't resist linking this dolmen.

I haven't checked it - but you could just use the centre of gravity for the whole table at (110,45) which should give you exactly the same result. Your reasoning seems correct otherwise.

I'd guess that 35kg is borderline unsafe.. (if I sat on the corner..)

if you want to have 4 legs - I recommend using lead/rubber/plastic spacers between table and legs to prevent wobbling - anything that can deform under weight - lead is a particularly good choice as it doesn't look out of place with concrete - just use some roofing lead folded over...87.102.86.73 (talk) 12:17, 25 July 2008 (UTC)

Out of curiosity, is there some reason to have the slab of concrete just be there instead of anchoring it to the pillars with... uh, crap, my vocabulary fails me here. I don't know what they're called, but one of those steel plate things, bent at a 90 degree angle? A couple of those would probably be quite enough to keep the slab from flipping even if someone were to sit on the other edge or something. -- Captain Disdain (talk) 12:44, 25 July 2008 (UTC)

Because the table isn't all that thick, only 4 or 5 cm. You could screw it down, but my father intends it to stay there for 15-20 years, and he doesn't want cracks to be formed. And 182 kg is a lot, so if you can eliminate the flipping risk, it'll stay there forever. ADFSGL (talk) 12:58, 25 July 2008 (UTC)

Well, you could probably get around the cracks by simply inserting steel rods or something into the concrete before it hardens and then hooking the metal plate thing into them, for example. That'd probably be easier on the concrete than drilling holes into it. (Well, maybe not; your father may well be more familiar with concrete than I am. It wouldn't take that.) In any case, if he's not willing to anchor it, you're probably going to just have to move that pillar. Or put some kind of a counter weight on top of the slab, but that'd take up table space and look less than charming. Another option that occurs: perhaps you could hook some kind of a weighted clamp on the other end of the table; done right, it would probably be pretty hard to spot. Still, not exactly the most elegant solution imaginable... -- Captain Disdain (talk) 14:10, 25 July 2008 (UTC)

In case you need a nudge towards being extra-cautious, here's a video demonstrating that concrete is heavy. --Sean 13:13, 25 July 2008 (UTC)

Hmmm ... 220 cm x 90cm x 5cm - I make that about 0.1 m³. Unless you are using pumice to make lightweight concrete, your weight calculations are on the low side - should be more like 230 to 240 kg [1]. That improves your stability, but unless you are an Olympic weightlifer, you will need a block and tackle or similar. Gandalf61 (talk) 13:28, 25 July 2008 (UTC)

I just checked with my dear old father, and he measured the thing to be 220cm x 90cm x 4cm. According to the manufacturer, the concrete has a density of 2300 kg/m^3, thus 182.16 kg. It's not lightweight concrete, but it is extremely fine-grained (the most fine-grained we could find). We did a test-table, and not only is it in a very nice eggshell-white, it's smooth as a cue-ball. ADFSGL (talk) 13:36, 25 July 2008 (UTC)

And you're right, there's no way we can lift it on our own, but we have recruited a merry band of assorted neighbours and relatives to lift it when it is dry enough tomorrow. We're going to be around six people. ADFSGL (talk) 13:38, 25 July 2008 (UTC)

I see I'm about to ask an entirely theoretical question: how come concrete? I've seen attractive cast-aluminum outdoor furniture. It doesn't rust, it's easy to move, and it doesn't look like it came from Joe Stalin's House of Outdoor Design. OtherDave (talk) 13:42, 25 July 2008 (UTC)

I had the same doubts as you, but it's actually very nice. The concrete isn't rough building-concrete, it's extremely smooth and very white, much prettier than metal. It's almost like marble, only not glossy and slightly more gray. It's also (very!) sturdy, it's not rickety or anything. It feels much more like a real table. ADFSGL (talk) 13:52, 25 July 2008 (UTC)

...unless it falls on you. A la the stability issue, why not replace that one pillar in the middle of the table with two pillars spread slightly apart? They don't have to be all the way to the edge, but spreading them a little will shift your fulcrum further from the center of gravity. Plasticup ^T/C 14:10, 25 July 2008 (UTC)

The design proposed seems unsafe to me, because it will cause the concrete beyond the pillars to be under a bending and sheering load, and concrete is quite weak under that type of load. Since concrete is best under compression, it would be better to use it, say, for the pillars themselves, and use some other material for the table surface. Also note that square, non-attached pillars will tend to concentrate forces on the table at the corners of the pillars, causing crack propagation and eventual fracture. Circular pillars would be better. If your dad insists on going with a concrete table surface, I suggest a thick steel "tray" (coated with weather-proofing material) underneath the concrete, capable of supporting the concrete and anything on the table, along with circular pillars. Here's a pic of a cantilevered concrete diving platform, which is similar to your table: [2]. Note the tapered side supports and lack of a center pillar (to prevent force concentratations). You can't see it, but I believe this design uses steel-reinforced concrete, with rebar inside the concrete. StuRat (talk) 15:25, 25 July 2008 (UTC)

Had you condsidered casting 'dumbell' shaped legs for a more organic feel:Organic architecture

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXTABLEXTOPXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
  LLLLLLLLLLLLLL                               LLLLLLLLLLLLLL
    LLLLLLLLL                                    LLLLLLLLL
     LLLLL                                         LLLL
       LL                                           LL
       LL                                           LL
       LL                                           LL
       LL                                           LL
       LL                                           LL
       LL                                           LL
      LLLL                                         LLLL
    LLLLLLLL                                    LLLLLLLLL
  LLLLLLLLLLLLL                               LLLLLLLLLLLLLL

87.102.86.73 (talk) 19:56, 25 July 2008 (UTC)

Just to be clear: if I'm not paying for the table, your dad can make it out of whatever he likes. The sturdy part I had no doubt about. OtherDave (talk) 01:42, 26 July 2008 (UTC)

I am not a structural engineer, but I rather share StuRat's concern about the bending strength of the concrete. Actually, you didn't specify whether you put any rebar in it; I'd suggest you do, but that may be too late if, as you imply, it's already cast and curing. Even with rebar, I think something like circular steel plates at the tops of the legs would be useful to spread the load, and coincidentally to expand the support a bit around the middle leg. I'd also be worried about the tabletop possibly sliding off the legs when pushed if it isn't attached to them, especially when the "floating" end is loaded (which reduces the load, and thus the friction, on the corner legs). —Ilmari Karonen (talk) 13:39, 26 July 2008 (UTC)

The concrete is indeed full of rebar, for exactly this reason. Anyway, I dug up the pillar (it's a wood pillar that's screwed to a cement plinth dug down about half a meter, btw) and moved it to about 35 cm from the edge of the table. We assembled the neighborhood strong-men and we lifted it on. It's steady as a rock now, nothing short of a 8.0 earthquake is going to move it, and there's absolutely no chance of sliding. It's just far to heavy for that. Anyway, thanks everyone for all your helpful tips and nice conversation! Me and pops are grateful. Here's a picture of the finished table:

It's slightly wet because we're using soap to create a smooth surface. Oh, and in the image, it looks like right pillar is a crooked, but that's 100% illusion, it's completely straight, so don't worry :) Cheers! ADFSGL (talk) 14:33, 26 July 2008 (UTC)

Your argument that it won't slide at all due to the weight isn't correct. I'd expect it to move over time, so you will have to occasionally reposition it. After all, glaciers and continents are a lot more massive, yet still slide over time. Incidentally, this table would represent an extreme risk to anyone sitting there during an earthquake, so I hope you're in a geologically stable area. StuRat (talk) 15:27, 26 July 2008 (UTC)

I'm in a very geologically stable area, so that's not a problem. As for the sliding, I tried with all my might to push it from the side so that it would slide and it wouldn't budge a millimeter. I think it'll stay where it is (friction does increase with the weight of the object, and this is a very heavy object. It might slide a little, but that's nothing that two strong men can fix in a minute) 83.188.214.253 (talk) 21:59, 26 July 2008 (UTC)

You probably can't break a hole in a cement sidewalk with just your hands, either, but a lowly weed can do it, given enough time. Many things that are difficult to move quickly are quite easy to move a little bit at a time. For example, it may vibrate a thousandth of an inch out of position each time a car drives by. StuRat (talk) 01:08, 27 July 2008 (UTC)

Well, if that happens, we'll notice it, and as I said, it only takes two strong men to lift it back into place. 83.188.214.253 (talk) 10:20, 27 July 2008 (UTC)

High Fructose corn syrup

I have been reading quite a few health articles about the ill affects of high fructose corn syrup (or corn syrup) and the bodies inability to process it. High Fructose Corn Syrup is an extremely sweet and cheap sugar altenative but it has very bad effects on the human body. It has been looked at quite a few times but always from the perspective of a user. Is there any other studies that have fully looked at the ill affects caused by corn syrup.

P.S It is used in almost everything we eat since the 1980s and the obesity rate has risen 37% since.

Rocco F Gervasi

Well, okay. Did you have a question about it, or...? -- Captain Disdain (talk) 14:00, 25 July 2008 (UTC)

Oh, geez, I must be going blind or something; I somehow completely missed the last sentence there. I'm sorry. -- Captain Disdain (talk) 14:01, 25 July 2008 (UTC)

I need a clarification myself. It sounds like you want to know about studies of the bad effects of corn syrup, but "not from the user perspective", which I suppose means "not from the consumer perspective". What perspective do you want ? Are you talking about people who come in contact with it during processing ? As far as I know, it doesn't cause any negative health consequences from touching it or inhaling fumes, if that's what you're after. Here's the Material Safety Data Sheet for corn syrup solids (powder): [3]. It looks like the two dangers identified are getting it in your eyes and a corn syrup dust and air mixture being explosive. StuRat (talk) 14:47, 25 July 2008 (UTC)

"User" could very well refer to the industrial users (the food companies). -- Coneslayer (talk) 14:50, 25 July 2008 (UTC)

Now I'm thinking you meant to ask "rather than look at nonrigorous studies by consumer organizations, I'd like to see some hard scientific data on the health consequences of consuming corn syrup, particularly it's relationship to obesity". Is this what you're asking ? If so, I'll let others answer, but would like to comment that having cheap, sweet goods available, in and of itself, may tend to cause obesity. StuRat (talk) 14:59, 25 July 2008 (UTC)

Not just that but there are many other things that happened in the 1980s, e.g. I was born then. I don't think anyone is going to say I'm the cause of the rising obesity rate. Nil Einne (talk) 17:29, 25 July 2008 (UTC)

• Well, I start with a search for HFCS negative effects, and the first thing that comes up is "The Negative Effects of High Fructose Corn Syrup on the Human Body". Google is your friend! --jpgordon^∇∆∇∆ 14:55, 25 July 2008 (UTC)

• Doesn't turning corn into syrup start with a smelly fermentation process, which is quite noticeable when driving by one of the factories? Could such manufacturing externalities have "ill effects" on neighbors? Edison (talk) 16:11, 25 July 2008 (UTC)

If you are looking for academic studies rather than general health articles you could also try a search at pubmed. "High fructose corn syrup" gave 97 hits, including this overview editorial from the American Journal of Clinical Nutrition which might be a good place to start. best luck, WikiJedits (talk) 20:09, 25 July 2008 (UTC)

For the record, Australia has similar rates of obesity to the US, but high fructose corn syrup is hardly used here. Personally I blame cars (lack of exercise) and the meat-sweet diet of the Western world. —Pengo 12:44, 26 July 2008 (UTC)

I blame the Internet. Apparently there are some people out there who spend a good portion of their free time editing online wikis instead of exercising. StuRat (talk) 06:03, 27 July 2008 (UTC)

Antimatter and matter

Why isn't there a perfect symmetry between antimatter and matter in the universe if they were formed from energy? Particles and antiparticles are produced in pairs, aren't they? —Preceding unsigned comment added by 116.68.79.122 (talk) 15:18, 25 July 2008 (UTC)

You are talking about CP-violation. As for why is exists, that is one of the biggest questions in particle physics. Hopefully the Large Hadron Collider will shed some light on that for us. Plasticup ^T/C 15:22, 25 July 2008 (UTC)

(edit conflict) Our relevant article is baryogenesis (and see also baryon asymmetry, CP violation). The question you ask is among the most important unsolved problems in physics. -- Coneslayer (talk) 15:25, 25 July 2008 (UTC)

Although the matter and antimatter are opposite to each other, but they actually do not follow the similar processes of integration and fragmentation.

To examplify, let us take the example of Proton and antiproton. Proton disintegrated to form electron and antineutrino during bigbang. But there can never be the breakdown of Antiproton to Positon and neutrino. Hence, there is no perfect symmetry between antimatter and matter. You may read the Book 'A brief History of Time by Stephen W. Hawking' as it provides a vivid description of answer of your questions.Asim Chatterjee (talk) 19:42, 25 July 2008 (UTC)

What in the world are you talking about? There is no evidence for proton decay, and there is also no proof that antiproton decay is impossible. I'm pretty sure they're on equal footing at the moment. Anyway, what you say would predict an imbalance towards more antiprotons and fewer protons, which is the opposite of what we observe! —Keenan Pepper 19:55, 25 July 2008 (UTC)

Pepper, you must know it that the total energy of the universe is zero. And according to the latest developments in quarks and quantum mechanics, proton decay can obviously take place. It has been shown in Fermi Lab that as a result of collison of proton and antiproton, top quark is evolved, which has anatural capacity to breakdown protons(and not antiprotons). But the idea of Roger Penrose regarding this is that the rate of antiproton decay, if it takes place at all, is obviously not comparable to that of proton decay. If you take into account the second step ionization equation of 'Saha Equation', you will no doubt find a possiblity leading to my statement being correct. Although we may see the positive universe, but it arose from a negative C-field as predicted by Hoyle. Even the General Theory of Relativity supports this statement.117.201.97.131 (talk) 21:04, 25 July 2008 (UTC)

Last I heard, there was no empirical evidence that proton decay could occur. Could you provide a link to something discussing these developments? --Tango (talk) 21:13, 25 July 2008 (UTC)

If proton decay occurred, it would still have to conserve baryon number and charge surely, which is totally at odds with what Chatterjee is saying. Philc 0780 17:58, 28 July 2008 (UTC)

I'm sorry, I can't as I am not yet too much familier with Internet because of being a new user. But you may consult the Book 'Meghnad Saha & Developments in Science'. There, in the middle of the third chapter, a set of ionization equations are there, derived from Dirac Equation which will help you to understand proton-decay.117.201.97.131 (talk) 21:24, 25 July 2008 (UTC)

Sign of the wavefunction

Hi! When I was learning atomic structure, the diagrams of orbitals had '+' or '-' signs marked on it(For eg., each lobe of a p-orbital had '+' on one lobe and '-' on the other). My teacher mentioned something about it relating to the wavefunction and addition/ subtraction interference or something like that, but I didn't get the point completely(I'm only in high school) I believe the wavefunction is a complex no., the square of whose magnitude gave the probability density. I don't understand what the sign means. Does it imply that the value of the wavefunction in one region is the conjugate of another?? Can anyone explain to me?? 116.68.79.122 (talk) 15:29, 25 July 2008 (UTC) A 15-year-old.

It's the sign of the real part of the wavefunction. (or if the wavefunction is not complex - just the sign)87.102.86.73 (talk) 15:44, 25 July 2008 (UTC)

" Does it imply that the value of the wavefunction in one region is the conjugate of another?? " - no, don't think that..87.102.86.73 (talk) 16:05, 25 July 2008 (UTC)

In general, the wavefunction is complex, but in the case of atomic orbitals, the eigenfunctions of the hamiltonian all happen to be real (or more correctly, you can multiply them by some complex constant to make them real). (I'm sure there's a good reason for this, but for now you can think of it as a mathematical accident.) The sign is simply the sign of the (real) wavefunction. 128.165.101.105 (talk) 19:51, 25 July 2008 (UTC)

But what does the sign physically mean?? 116.68.79.122 (talk) 07:52, 27 July 2008 (UTC) A 15-year-old.

For a single orbital in isolation, it has no physical meaning. It only means something when different orbitals combine, for example when two atomic orbitals combine to form a molecular orbital. If parts of the orbitals have the same sign, they fuse together, allow the electron to delocalize more, and lower the energy. If they have opposite signs a node forms between them and it raises the energy. See Linear combination of atomic orbitals and MO diagram. 128.165.101.105 (talk) 14:33, 28 July 2008 (UTC)

Neonatal Circumcision as a preventative measure against HIV...

Does neonatal circumcision help prevent the possibility of contracting HIV? Unfortunetly much of the research on the subject is highly biased either in favor for or against circumcision. I understand there is much debate on the subject and a list of medical journals or articles explaining the medical aspect of the procedure as a preventative measure without bias would be greatly appreciated. 65.9.252.237 (talk) 17:46, 25 July 2008 (UTC)

I don't know about neonatal circumcision specifically, but I remember reading a study conducted by a UN group that ended early because the results were so heavily in favor of circumcision reducing HIV transmition that they deemed it unethical to continue keeping a control group of uncircumcised men. Plasticup ^T/C 17:56, 25 July 2008 (UTC)

Does it really matter? I never understood what the point of the study was. Just wearing a condom or even better, not having sex with HIV infected women seems to be a better option than circumcision. The simplest solution is always the best solution. ScienceApe (talk) 18:57, 25 July 2008 (UTC)

The studies are all a little dicey as circumsized/uncircumsized men tend to represent different cultural samples and all this so take some salt, but yeah, circumcision reduces the transmition rate of HIV. It also reduces the occurances of trench foot in your penis if you're drafted to fight in World War I. WilyD 19:08, 25 July 2008 (UTC)

To be specific about the question though, neonatal circumcision is not shown to affect HIV transmission rates. Being circumcised has been shown effective in some populations where the males are non-monogamous and unprotected during sex (per ScienceApe) - neither of these criteria apply to a 4-year-old boy. The difference between circumcision and neonatal circumcision is that the neonate is not given a choice. Franamax (talk) 19:38, 25 July 2008 (UTC)

Err, as long as it's not so recent that you're not completely healed, the exact time of circumcision doesn't matter. It's probably not effective against many methods of HIV transmission, such as blood transfusions and sharing needles. WilyD 16:37, 26 July 2008 (UTC)

Plus, ending a study early due to strong results (as happened with, I believe, all the studies on HIV transmission and circumcision in adult African men) leads to skewed results which are not really that useful. Who knows if the difference in infection rates would have been anywhere near as pronounced after 5 years? After 10? And, of course, you cannot necessarily extrapolate to different populations behaving in different ways being infected with different HIV. 79.66.124.253 (talk) 21:29, 28 July 2008 (UTC)

Catalyst?

In the reaction '2SO₂+O₂=2SO₃', the required conditions are 1:Presence of 450^oC temperature and 2:A catalyst Now this catalyst can be either Vanadium Pentoxide or Platinum in general. But among these two, which catalyst pprovides a better speed of reaction?Asim Chatterjee (talk) 19:33, 25 July 2008 (UTC)

According to Contact process platinum is the better catalyst.87.102.86.73 (talk) 20:14, 25 July 2008 (UTC)

Yes, I think platinum is much more expensive, so why would anyone use it unless it worked better? —Keenan Pepper 20:48, 25 July 2008 (UTC)

It is, they don't, it does... but the platinum is more easily poisoned according to reports. Otherwise they would use it if it allows the reaction to occur at a lower temperature (which is almost the same as having faster reaction rates - one follows the other..)87.102.86.73 (talk) 21:04, 25 July 2008 (UTC)

You are most welcome for having me helped,User-87.102.86.73.You are truely among the most brilliant persons I've ever talked to.Thank you. —Preceding unsigned comment added by 117.201.97.131 (talk) 21:19, 25 July 2008 (UTC)

Thank you very much, but please don't thank me, thank those who wrote the articles and did the research in the first place, and of course thank wikipedia..87.102.86.73 (talk) 21:23, 25 July 2008 (UTC)

Yeah, I'll surely do the same.But I can't ignore your efforts. I shall be ever grateful to Wikipedia.117.201.97.131 (talk) 21:27, 25 July 2008 (UTC)

Collisional quenching rate constants for some excited states of N₂ and N₂⁺ in helium

I don't really expect this to be answered here, but I figure it's worth a shot. The RD has surprised me before!

I'm interested in the C³Π_u state of the N₂ molecule, and the B²Σ_u⁺ state of the N₂⁺ molecular ion. I need to know the reaction rate constants for the collisional quenching reactions of these species when they collide with ground-state helium atoms. If experimental data are not available, I need some theory that will allow me to estimate these rate constants to at least order-of-magnitude accuracy. All responses appreciated. —Keenan Pepper 20:07, 25 July 2008 (UTC)

This pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740002549_1974002549.pdf mentions in the references "reaction rates for collisional de-excitation of B²Σ⁺_u states of N₂⁺..." see Ref 4. but doesn't mention what in.. The article itself also mentions measurements in helium, but I didn't read it all to check it..87.102.86.73 (talk) 21:01, 25 July 2008 (UTC)

Insect Survival

How long can insects survive in a vacuum? Does their exoskeleton help protect them? Just curious. Horselover Frost (talk) 22:03, 25 July 2008 (UTC)

You'll find several papers with Google Scholar and the keywords insects vacuum. However, you'll need a library visit if you want to know the complete picture, as some abstracts aren't online. What I could gather was that insect eggs aren't affected by low pressure plus low temperatures, but are vulnerable with longer exposure or higher temperature (Mbata et al., Mortality of Eggs of Stored-Product Insects Held Under Vacuum: Effects of Pressure, Temperature, and Exposure Time) and that At 50±5 mmHg, the egg stage was the most resistant in all three species, times needed to obtain 99% mortality being 45, 49 and 22 h, respectively. (Finkelman et al., Effect of low pressures on the survival of three cocoa pests at 30°C) which would give an upper bound to the answer to your first question. --Ayacop (talk) 05:57, 26 July 2008 (UTC)

Shark vs. Crocodile. Who is stronger?

In a confrontation between both. 190.49.102.65 (talk) 22:04, 25 July 2008 (UTC)

Well ignoring the fact that a shark is a blue water animal while the crocodile is a brown water animal... Actually it's almost impossible to answer because the environment would dictate who would win. A shark is not "designed" to swim in shallow brown water, where a croc lurks. Likewise, a croc can't swim forever, and would drown in open blue water. So in brown water, the croc, in blue water, the shark. Probably. ScienceApe (talk) 22:17, 25 July 2008 (UTC)

Animal Face-Off says it all - shark is the winner.87.102.86.73 (talk) 22:33, 25 July 2008 (UTC)

Those face-offs are pretty ridiculous. Incidentally they also said a lion would win in a fight against a tiger. This match-up has actually occurred a few times in captivity, and the tiger almost always wins. ScienceApe (talk) 00:47, 26 July 2008 (UTC)

Which would seem obvious from their respective sizes (tigers are HUGE). --Ayacop (talk) 06:02, 26 July 2008 (UTC)

Actually the Saltwater crocodile does at times swim in the open ocean, according to our article. Considering the fact that "Salties" can be 20 feet long and weigh more than a ton, a shark might come out second best. Consider also that crocodiles are well armored over much of their body. --Eriastrum (talk) 19:33, 26 July 2008 (UTC)

Alligators are seen rarely in the ocean[4] while bull sharks are occassionally found hundreds of miles up freshwater rivers. Rmhermen (talk) 20:40, 26 July 2008 (UTC)

Don't confuse alligators (Family Alligatoridae) with crocodiles (Family Crocodylidae). They are very different animals. Alligators (genus Alligator, found only in southeastern United States and in China's Yangtze River) are almost always found in fresh water. The Crocodile I was referring to is the Saltwater Crocodile (Crocodylus porosus) that is very definitely found in salt water, including ocean far from land. It is native to Southeast Asia and Australia. --Eriastrum (talk) 21:57, 26 July 2008 (UTC)

Electronic interference on airplanes

Hello. Does leaving on your "portable electronic devices" prior to take off/landing on an airplane really have any interfering effect in the cockpit? It just seems to me that even if everyone on a plane had a CD player with headsets on, there could not possibly be enough interference to inhibit cockpit communication with the airport, or to distort the autopilot. Also, would cell phones in operation during flight cause a technical problem either? I've seen a stewardess use a credit-card scanner during flight that sends a signal to accept the charge, which to me would seem to have the same interfering effect as a cell phone, yet the scanner is allowed to be used. It makes me think that cell phones are prohibited just for the sake of passenger comfort (no one wants to sit next to someone who yells on their cell phone the whole flight). Comments? Answers? Thanks!--El aprendelenguas (talk) 22:05, 25 July 2008 (UTC)

On more thing: After the plane has landed, why is it okay to use cell phones at that point but "all other electronic devices should remain off"? Thanks!--El aprendelenguas (talk) 22:12, 25 July 2008 (UTC)

See Mobile_phones_on_aircraft#Current_status. The gist of it is the FCC forbids the use of cell phones on planes in flight (based on some evidence that they can interfere with navigational equipment), while the use of cell phones on the ground is up to the FAA, who may permit or forbid cell phone use as they see fit. Horselover Frost (talk) 22:22, 25 July 2008 (UTC)

Mythbusters aired an episode where it tested the claim. The answer was no, it doesn't effect the airplane's electronics, they just ask people to turn them off just to be safe, because there might one day be an electronic device that might have unforeseen effects on instrumentation. ScienceApe (talk) 22:25, 25 July 2008 (UTC)

The UK Civil Aviation Authority did a study in 2003 that determined that interference from cell phones may disrupt the functioning of the electric compass used in airplanes. (study and results here) Horselover Frost (talk) 22:36, 25 July 2008 (UTC)

The irony is that the alternative, the in-flight entertainment system, has already caused at least one crash, while there's no record of CD players, cell phones, etc., causing a crash. Therefore, I'd prefer if they kept all that unneeded hidden wiring off the plane and let people use their own, much safer, devices. StuRat (talk) 23:28, 25 July 2008 (UTC)

Personally I'm glad from a personal standpoint that cell phones aren't operated on planes. Businessmen on planes are irritating enough ("So I SAID to the GUY, buy LOW, sell HIGH, ya'know what I'm SAYIN'?") without being able to communicate with people outside of their seats. But the other electronics—totally silly to have them switched off for takeoff and landing, but whatever. --98.217.8.46 (talk) 03:27, 26 July 2008 (UTC)

(As an aside, this is my favorite comic on the subject.) --98.217.8.46 (talk) 03:27, 26 July 2008 (UTC)

I liked the Simpson's episode where the stewardess made Bart turn off his game. Then the plane's engines quit and it went into a dive. Next the stewardess said "turn it back on !", and the problem was fixed once Bart did. StuRat (talk) 04:44, 26 July 2008 (UTC)

Bear in mind that for large items like laptops, one of the reasons your supposed to switch them off is because you're also supposed to put them away so they don't become dangerous flying objects in an emergency. As for devices like CD players etc, I suspect one of the reasons why your supposed to switch them off is so you're not listening to them and can actually hear any annoucements and instructions in an emergency (supported by this reference [5]) Nil Einne (talk) 20:15, 26 July 2008 (UTC)

EMP against guns

If an E-bomb or EMP weapon was used against soldiers armed with guns, would it ignite the smokeless powder, and cause the guns to explode? ScienceApe (talk) 22:23, 25 July 2008 (UTC)

Do you mean conventional mechanical guns, or electrically operated guns? Horselover Frost (talk) 22:28, 25 July 2008 (UTC)

Mechanical guns like M16 or AK47. ScienceApe (talk) 00:44, 26 July 2008 (UTC)

Then no, or at least it didn't happen when the U.S. Military tested EMFCGs back in the late 70s. And I don't see how it could happen, since the effects of an electromagnetic pulse on a conventional firearm would be roughly the same as a shock from static electricity. Horselover Frost (talk) 04:21, 26 July 2008 (UTC)

Possibly not - if the gun is metal and the cartridges inside the gun the metal of the gun might absorb most of the EMP.87.102.86.73 (talk) 22:35, 25 July 2008 (UTC)

Metal doesn't absorb though, it's a conductor. ScienceApe (talk) 00:45, 26 July 2008 (UTC)

A conductor will reflect em radiation —Preceding unsigned comment added by 79.76.216.89 (talk) 02:03, 26 July 2008 (UTC)

Also, if you try to argue that it may conduct or reflect and, as a result, produce heat... The heat of the Mojave (and Iraqi) desert hasn't caused round to explode. -- kainaw™ 18:15, 26 July 2008 (UTC)

Why do some birds have long tails?

Why exactly is it that some bird species have evolved long tails whilst other species in the same family with broadly similar behaviour have not?

Compare the European Magpie and the Carrion Crow, or the Peach-faced Lovebird and the Budgerigar, for example. What exactly are the benefits to a bird of having a long tail anyway? --Kurt Shaped Box (talk) 23:30, 25 July 2008 (UTC)

Good question. A common answer to "what is a long tail good for?" is either "balance" or "showing off". The latter normally implies a pronounced sexual dimorphism, which for the birds you mention is not the case; so balance (in flight, perched, or on the ground) would be the first thing that comes to mind. However, I have found this abstract, which suggests that the long tail serves for the potential mates as an indicator of overall physical condition of the bird (and therefore its reproductive potential). The suggestion is very interesting, but not necessarily correct. Another thing that can not be ruled out is that a long tail is meant to confuse predators, either by increasing the perceived size of the bird or by moving the potential point of attack away from the vital areas. The tail is graded, so it is not very bulky for its length; but a magpie really looks bigger than it really is: a typical magpie weights 200-240 gram, a typical carrion crow about 500. Hope this helps (I doubt it though...). Best regards, --Dr Dima (talk) 01:13, 26 July 2008 (UTC)

One factor is manuverability. For example, raptors that are soaring birds that largely fly in wide open areas have short, broad tails (example, golden eagle shown here [6]). However, raptors such as accipitors that hunt their prey in wooded areas have distinctly longer and narrower tails (for example, see this Sharp-shined Hawk here [7]). And then there are forest birds, like ant pittas [8] that spend almost all their time on the forest floor and have almost no tail at all--presumably because they don't need it. However, when it comes to the more extreme examples of long tails it is probably related to sexual selection. For example, motmots [9] or squirrel cuckoos [10]. This is certainly the case in the the longest tails of all, the lyrebird [11], for example.--Eriastrum (talk) 22:28, 26 July 2008 (UTC)

Thanks very much for the thoughtful answers, folks. On the 'confusing predators' angle - is it the case that the tail feathers of long-tailed birds will generally come out at the root quite easily if something catches ahold of them? I've found myself wondering this whenever I've been trying to pick up one of my (very quick, very manoeuvrable - even in a cage) budgies. On more than one occasion now, I have ended up with a fistful of tailfeathers but no bird in the hand (man, I feel so guilty whenever that happens). It wouldn't surprise me one bit if a magpie couldn't just leap away from its tail if a cat had it's jaws around the other end. --Kurt Shaped Box (talk) 07:15, 27 July 2008 (UTC)