Science desk
< April 21	<< Mar \| April \| May >>	April 23 >

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.

April 22

Platinum versus carbon

We are conducting an experiment in hydrolysis with various electrolytes, anodes and cathodes. Before getting started we would like to clear something up. Since platinum is used as a catalyst to assist chemical reactions which is safer to use in the production of hydrogen and oxygen gas (which might be together in a beaker as they are liberated through the process of electrolysis), a carbon rod or a platinum rod? 71.100.8.252 00:11, 22 April 2007 (UTC)[reply]

The definition of catalyst is that it is consumed in the intermediate reaction and regenerated as product so the overall reaction looks like it doesn't get used up. So using a carbon rod is as safe as platinum rod. But if you really want to argue, carbon rod is safer because platinum is a metal and conducts electricity better than carbon. OhanaUnited 05:57, 22 April 2007 (UTC)[reply]

Platinum will catalyze burning of hydrogen so I'd take the carbon. This was question to test WP, right? --85.179.17.199 16:32, 22 April 2007 (UTC)[reply]

No, its a for real question. Back when platinum did not cost so much I think they had a Zippo lighter that used platinum to ignite Naptha vapors spontaneously whenever you could finally get the top open to allow oxygen to enter and start the combustion reaction. If I'm right Zippo stopped making them because users could not just flip the lid and strike the thumb wheel but had to use both hands to get the top open which made it much more difficult to light up than using a conventional lighter. I think they could also despite all of the saftey precautions open up in your pocket. 71.100.8.252 05:40, 23 April 2007 (UTC)[reply]

snails

I was gardening today and had noticed a silvery coating on some old pieces of bark....then later I notice of silvery trail reflecting in the sun, and on inspection saw it was a snail leaving a slimy, beautiful trail behind him....is this common? —The preceding unsigned comment was added by 70.41.134.125 (talk) 00:50, 22 April 2007 (UTC).[reply]

I believe all land snails and land slugs leave a mucus trail behind them, fitting your description. [Mαc Δαvιs] ❖ 01:07, 22 April 2007 (UTC)[reply]

Have a look at this page for more info: [1]. - Akamad 01:09, 22 April 2007 (UTC)[reply]

(re) permanent magnet

i know you can demagnetise a magnet with an impact but if i need to put a magnet in something that will recive impacts (average 10 to 20 pounds force), if i try to dampen the impact with a layer of rubber or something better would it be easy or at least possible to lower it enough to not any magnetic strenght?

also if that changes anything, the magnet needs to be in a magnetic fiels repulsing it —The preceding unsigned comment was added by 216.113.99.21 (talk) 05:05, 22 April 2007 (UTC).[reply]

I doubt it matters much whether the magnet is being repelled by another at the time of the impact - but even a small amount of cushioning will certainly help immensely. Whether it helps enough in your application depends a lot on the nature of the magnet you are using - the rate of decelleration of the mass hitting the magnet - and probably a whole bunch of other things besides. You could perhaps consider using an electromagnet - so long as it's not mechanically damaged, it would be completely resistant to impacts. SteveBaker 05:13, 22 April 2007 (UTC)[reply]

it cant be an electromagnet be an electromagnet , what kind of materials would be the best?

Not sure exactly what would be the best, but be wary of supermagnets, like neodymium magnets. These and other supermagnets tend to be extremely brittle, so they'll need quite a bit of padding if you want to use them. I'm not sure what to actually recommend, though. Someguy1221 07:29, 22 April 2007 (UTC)[reply]

the cheapest possible

no, the second most expencive is usually best.

archetectural spesification for cinemahall in india

what are specified requerment for cenemahall in india sp U.P. Mainly distance of screen from first row ,gap btween seat rows,no.exhust fans,toilets,entery and exit gates etc as per the person capicity. —The preceding unsigned comment was added by Rajharshchauhan (talk • contribs) 07:58, 22 April 2007 (UTC).[reply]

I believe you mean a cinema hall (movie theater). Since those regulations might vary by location, can you be more specific as to your region of India ? StuRat 08:22, 22 April 2007 (UTC)[reply]

Looks like he tried! I'm guessing "sp U.P." meant "specifically, Uttar Pradesh... —Steve Summit (talk) 15:34, 22 April 2007 (UTC)[reply]

I'm glad you interpreted that, I was wondering why he was interested in regs for the Upper Peninsula of Michigan. :-) StuRat 19:18, 22 April 2007 (UTC)[reply]

Chemical activity

In chemistry the concentration of a species A is denoted by $[A]$ , but for chemical activity the square brackets should be replaced by curly brackets - {A}. How can the square brackets in math expressions such as the one below be replaced by curly brackets, given that curly brackets have a special significance in the math system?

K={\frac {\left[C\right]^{c}\left[D\right]^{d}}{\left[A\right]^{a}\left[B\right]^{b}}}

Petergans 12:15, 22 April 2007 (UTC)[reply]

How does this look? I replaced \left[ with \{, and \right] with \}

K={\frac {\{C\}^{c}\{D\}^{d}}{\{A\}^{a}\{B\}^{b}}}

Meta probably describes it somewhere: meta:Help:Displaying a formula. The Wikipedia:Help desk might have some other tips. --HappyCamper 13:46, 22 April 2007 (UTC)[reply]

AC transformers

If I connect a DC power source to an AC transformer, what happens?--172.131.238.148 12:38, 22 April 2007 (UTC)[reply]

As you presumably know, inductors and transformers do interesting things with AC (or, at least, with time-varying currents), not DC. So, to start with, do you know what happens if you apply a DC voltage to a simple inductor? —Steve Summit (talk) 15:31, 22 April 2007 (UTC)[reply]

Woo woo, I know, I know! --Wirbelwindヴィルヴェルヴィント (talk) 17:28, 22 April 2007 (UTC)[reply]

Put your hand down, Wirbelwind. Ten points from Gryffindor for being an insufferable know-it-all. --Severus Snape —The preceding unsigned comment was added by Ummit (talk • contribs) 18:18, 22 April 2007 (UTC).[reply]

Well, I was going to answer and explain what happens, but I figured you wanted him to figure it out for himself, so I refrained. --Wirbelwindヴィルヴェルヴィント (talk) 18:48, 22 April 2007 (UTC)[reply]

(Yes, of course, and very well you did, unlike the poster below, who always seems to have to try to keep up with his namesake... :-) —Steve Summit (talk) 21:34, 22 April 2007 (UTC))[reply]

Now, now, comment on the post, not on the person. See WP:NPA. If the questioner were an advanced physics student or electrical engineer, he would likely not have asked the question. It is a normal function of the Ref Desk to actually answer the question, rather than teasing the questioner. Edison 04:18, 23 April 2007 (UTC)[reply]

There may be an excessive current, causing damage to the DC power supply. A transformer winding generally offers less opposition to direct current than to the alternating current it is designed for. If the DC voltage is low enough that the current flow is acceptable, then the current will rise to a maximum, opposed by the [inductance]] of the winding. There will be a pulse of voltage in the other windings(s) of the transformer when the DC current flow begins in the winding energized by the DC source. Engineers may sometimes use a small battery in this way to test the polarity of transformer windings. The voltage may be surprisingly high in the output pulse. One a steady state current is established, there will be no DC voltage on the other windings. When the current in the source winding is stopped, there will be an opposite pule of voltage in the other windings. There may be a high voltage pulse present in the winding connected to the battery when the current is broken. This phenomenon was discovered by Michael Faraday in 1831. His first transformer is on exhibit at the Royal Institution and still works.Edison 19:11, 22 April 2007 (UTC)[reply]

Some DC power supplies, such as half wave rectifiers, or full wave rectifiers without capacitor filtering, have a substantial amount of ripple which might show up as a distorted AC waveform on the other winding. Edison 04:18, 23 April 2007 (UTC)[reply]

How long has most meat been dead in the super market?

I know this is a huge question, but I'm just looking for a ballpark figure. I'm not talking about frozen meat or meat in pre-packaged food (although I'm curious about those as well) -- I'm just looking for any information about how long ago the meat from the packaged meat counter was slaughtered. Anyone know? Days, weeks... months? Thanks in advance! -Quasipalm 16:17, 22 April 2007 (UTC)[reply]

I would say 5-10 days would be typical. Of course cow meat has to be aged a good while before it's considered edible. Vranak

Wet aged beef suggests 3 days aging for the modern technique, while dry aged beef may age for 15-28 days. This is strictly aging time- there would be some additional time spent in overhead, presumably. And this is just beef- many kinds of meat don't get aged at all. When the meat in question hasn't been frozen or cured, this suggests a fairly short time limit on how long it could spend sitting in refrigerated places and still be considered safe to eat. Friday (talk) 17:07, 22 April 2007 (UTC)[reply]

Very interesting, thanks! -Quasipalm 17:30, 22 April 2007 (UTC)[reply]

Passing uric acid crystals in the urine?

This is one of the symptoms of some kidney problem (I don't remember the finer details) that a family member's cat has been diagnosed with. Am I correct in thinking that the cat will be in agony every time he urinates (AFAIK, uric acid forms a very sharp crystalline structure)? He apparently holds on for almost a day between pisses - which would make sense if this were the case... --Kurt Shaped Box 16:17, 22 April 2007 (UTC)[reply]

Humans usually feel pain only at the moment of stones passing the urethra. Pain in the ureters or kidneys are less specific but also of short duration. My guess is rather a bladder infection which leads to continuing pain in bladder and urethra. --85.179.17.199 16:24, 22 April 2007 (UTC)[reply]

Male cats are particularly prone to urinary blockage caused by urinary crystals; this is considered a veterinary emergency, as kidney failure and death can occur in as little as a day if the blockage is not resolved. If a cat is prone to develop crystals (and urate crystals are only one of several possibilities), they will usually be put on a prescription diet to prevent recurrences; if recurrences nonetheless happen, sometimes surgery can be helpful. In any case, this is something that a veterinarian has to treat. Further information can be found here. - Nunh-huh 17:03, 22 April 2007 (UTC)[reply]

Thanks for the info. As far as I know, the cat is getting better now - I think that the vet did put him on a new diet as it happens... --Kurt Shaped Box 20:21, 22 April 2007 (UTC)[reply]

We actually have an article on it, if you're interested: Feline lower urinary tract disease. --Joelmills 21:50, 22 April 2007 (UTC)[reply]

My experience (and my urologist's information) is contrary to what .199 said: my understanding is that the ureters are quite inflexible, so subject to much more pain than the somewhat-flexible urethra when the stone passes. I personally had a kidney stone that was murder at first (in the ureters), but I never even felt it when it left my body through the urethra. --TotoBaggins 01:52, 23 April 2007 (UTC)[reply]

Uv Sestive Materials

I would like to know if there are any materials that are uv sensite (not light sensetive). A material that, when exposed to a certain amount of uv light, will react in some way. It can either be to change color or to change shape, form or size.

Thank You 17:29, 22 April 2007 (UTC)~ Tertius F.

That depends. There are a lot of materials that are sensitive to ultraviolet to varying degrees. It depends on how much sensitivity you need – how much (or how little) UV do you need to detect &ndsah; and whether or not you need a reversible/reusable process. Do you want something that reads out an average dose over a long period of time, or a fast readout for the intensity of UV right this minute?

Even an ordinary sheet of white paper will fluoresce under intense UV illumination; there are a number of dyes which are brilliantly fluorescent under UV. A number of minerals are also fluorescent under ultraviolet; see Image:Fluorescent minerals hg.jpg.

Many dyes fade on prolonged UV exposure, but are also sensitive to visible light. A side-by-side comparison of a material under glass (no UV exposure) and the same material without shielding will show a difference in rate of fading that can be largely attributed to UV. TenOfAllTrades(talk) 18:20, 22 April 2007 (UTC)[reply]

Though it seems you are after a physical response, there are many semiconductors that have a photoelectric response to UV wavelengths. Practically anything with a band gap energy under about 4 eV will respond, though higher band gap energies are preferable for more sensitive detection due to thermal noise and higher response to lower energy wavelengths. -- mattb 18:35, 22 April 2007 (UTC)[reply]

On Texas driver licenses, there's markings that appear only with UV light. Specifically, it'll glow with several watermarks saying Texas. I'm not sure what that material is though. --Wirbelwindヴィルヴェルヴィント (talk) 18:44, 22 April 2007 (UTC)[reply]

Probably some fluorescent material, as TenOfAllTrades mentioned above. -- mattb 20:21, 22 April 2007 (UTC)[reply]

UV sensitive Materials

Hi

I'm a noob so that's why im doing it like this.

The thing is, the uv sensitive material I'm refering to should be something in the line of AgCl or something like that. I know AgCl is used in photo's, not that Im looking for the same reaction(coping of an image, rather the color change properties). The project Im working on needs at least one example of a substance that will change color after a certain amount of time in the sun (uv rays). Maybe some sort of silver halide that one can put in paint that darkens after a certain amouth of exposure to uv rays?

The problem is, it should react to the uv rays but not the light.

Or... Is there an invention that can measure uv rays like the radion patches that people wear who work in nuclear facilities. Something that detects uv rays and can give an indication according to how much rays it has absorbed?

Thanx again T.F —The preceding unsigned comment was added by 196.207.47.60 (talk) 18:54, 22 April 2007 (UTC).[reply]

What do you mean react to UV rays but not the light? Solar rays have UV rays, so it'd be kinda impossible for it to react to UV rays but not UV ray from certain sources. --Wirbelwindヴィルヴェルヴィント (talk) 19:03, 22 April 2007 (UTC)[reply]

What I mean is, that it should react to UVA or UVB rays. The other possibility is if the material in question were to be able to react to light in the same amount of time that it absorbes uv rays. sort of like Time/Light = Time/UV rays. (some strange formula, i know)

The problem is, that lets say its paint on a wall, one day it will take the wall 3h to change color, and other days it will take 6h, just as long as its able to indicate that the paint has absorbed a certain amount of uv rays.

In that case, you would need a phosphor that absorbs UV light to radiate visible light. Something along the lines of what is used as optical brighteners that react to UV light and glows, and de-energises after awhile (much like glow in the dark toys). However, I'm not sure which phosphor fits those criterias, and the optical brighteners is the closest I can find on wikipedia. --Wirbelwindヴィルヴェルヴィント (talk) 19:23, 22 April 2007 (UTC)[reply]

Thanx it help a lot. Not exactly what I had in mind but I can see it working in my project. You have been a great help.

Cheers T.F

Check out our article on photochromism. What you want is a photochromic material with an absorption spectrum in the UV region. --mglg_(talk) 20:36, 22 April 2007 (UTC)[reply]

Mystery insect - anyone know what this is?

There was a strange insect fluttering round my room the other night, and I have no idea what it was. I got a photo of it when it was sitting beside my laptop - for the purposes of scale, the green thing is the plug on my mouse, and it's about 1 1/4 inches long. It didn't buzz at all (just clattered a bit against the wall as it flew), and didn't seem distressed by my being there. I've googled phrases like "picture guide to insects" and had a flick through the article Insect (and related articles too), but can't find anything helpful - does anyone know what this thing is? I'm in southern England at the moment, if that's any help. --ZsigE 20:05, 22 April 2007 (UTC)[reply]

Looks like a caddisfly to me. See this image off google search. --Wirbelwindヴィルヴェルヴィント (talk) 20:38, 22 April 2007 (UTC)[reply]

Aha! That looks about right. Thanks! --ZsigE 20:42, 22 April 2007 (UTC)[reply]

Gymnena sylvestre and Garcinia Cambogia

Can you tell me if there are any contraindications or interactions from/with other meds. or herbs? I have looked on many cites including wikipedia. I can't find any thing concerning interactions or contraindications. Thank you curlyhorse

Wikipedia cannot give medical advice. I would suggest asking your medical practitioner. Splintercellguy 00:14, 23 April 2007 (UTC)[reply]

and do you seriously expect that they will know? :)

(as a start, the usual spelling is "Gymnema sylvestre") I would call your physician's attention to [2] "DrugDigest is the consumer health and drug information website of Express Scripts, Inc. (ESI), the nation's largest independent pharmacy benefit manager (PBM). Through its corporate relationships, ESI designs and manages prescription drug plans.... The goal of DrugDigest is to provide ESI members and the public with the information they need to lead healthier lives. " it's a professionally responsible source that includes scientific references. I consider it appropriate for librarians to give references to sources of reliable information, though not to provide medical advice. DGG 03:40, 23 April 2007 (UTC)[reply]

physics

title- nuclear physics question-explain what would happen in a nuclear reactor if the coolant fluid leaked out of the core? —The preceding unsigned comment was added by 82.29.69.23 (talk) 20:50, 22 April 2007 (UTC).[reply]

Think about the consequences of having an uncooled or inadequately cooled fission (I'm assuming) reactor core and the potential hazards of the coolant itself (what exactly that is depends heavily on the reactor type). Ever heard of Three Mile Island?-- mattb 20:56, 22 April 2007 (UTC)[reply]

title-referencedesk response to homework problem-read China Syndrome. Edison 21:00, 22 April 2007 (UTC)[reply]

Or see the pretty decent Fonda/Douglas film based on the book. -- mattb 21:08, 22 April 2007 (UTC)[reply]

It depends on the kind of reactor you've got. There exist designs that would not melt down if the coolant went away. --TotoBaggins 01:39, 23 April 2007 (UTC)[reply]

I'm assuming you mean primary coolant. In my understanding, nuclear reactors emit neutrons that are either "fast" or "slow". In some designs, the coolant is the moderator and turns the useless fast neutrons into slow ones. Therefore, if the primary coolant is removed, there are not enough slow neutrons to sustain the reaction and the core cools. Loss of secondary coolant may result in problems however. In other designs, the coolant is not the moderator and loss of coolant and moderator results in thermal runaway. --Tbeatty 04:03, 23 April 2007 (UTC)[reply]

All science a philosophy

I asked this question on the humanities desk and it was suggested I ask it here also.

Ok, so we base out mathematics on axioms, things we accept without proof (such as one plus one equals two). If we accept something without proof, it is a philosophy. So wouldn't that make all of math a philosophy? That would be alright, it is just that we use math as the language of science. So wouldn't that make all our science equations written in math just a philosophy? Just our interpretation of the universe? I suppose this would supported by the fact that quantum mechanics has many different interpretations, and you can even take classes on the philosophy of quantum mechanics [3]. Isn't this kind of a big deal that all of our science may not be leading us to the reality, but only one interpretation of it? Imaninjapirate^{talk to me} 22:06, 22 April 2007 (UTC)[reply]

Science is a systematic explanation of phenomina we observe. One plus one equals two simply because of the way we've chosen to define the notions of one, two, addition, and equality. You don't have to prove that one plus one equals two, because the numerals and operators are defined to make it true and self-consistent. Your example of quantum mechanics merely shows the difference between science (QM) and the philosophical implications of science. QM is a description of how things behave on a very small scale. This description is considered "pretty good" because it has accurately predicted measurable phenomina time and time again. QM is not considered to be some fundamental truth, just a model for describing what we observe. If you want to use the results of QM to speculate about some greater meaning or about that which we cannot observe, you've ventured into the realm of philosophy. -- mattb 22:27, 22 April 2007 (UTC)[reply]

Mathematics is, certainly, an abstract system of thought grounded in nothing but its own internal consistency. I suppose you could call it a "philosophy" if you wanted to, although you would be doing it (and perhaps philosophy as well) no favors by the comparison, because the level of rigor in mathematics is nothing like the level of speculation in philosophy.

But even if mathematics is a philosophy, that does not make science one. Mathematics is merely a tool used by science, and science doesn't use anything that doesn't work. (As it happens, mathematics is a very, very good tool that serves science very, very well, but that still doesn't imply that mathematics's quasi-philosophical nature rubs off on science.)

Actually, come to think of it, depending on your definition of "philosophy", you could call science a philosophy, too, for all I care. Certainly there is a field of inquiry called the "philosophy of science" in which we try to explain how and why science works. My own philosophy of science is that for the domains it studies, science comes as close to absolute objective truth as it is humanly possible for us to do.

Now, of course, "absolute objective truth" is a slippery concept, as the philosophers can tell us. Moral relativism is always fashionable; there are always people spouting that you can believe any truth you want to believe. But the truth that science teaches us is different: it's grounded in our repeatable observations of the world (and universe) we live in. If a discrepancy is found between one of science's explanations and the way the real world is observed to work, science tinkers with its explanations until they match. 1 + 1 = 2 may be an unproveable axiom in mathematics, but science insists on scientific proof (not mathematical proof) for all of its theories.

Given the success that science has had, given the level of scrutiny that every one of its explanations has received, it's rather foolish to dismiss science as "just another belief" which anyone is free to accept or not. There can be little doubt that science works: ever since we noticed that we could plant seeds and have them grow into food we can eat, we've been seeking and refining explanations for the way the world works, explanations which help us live our lives more easily (or at least more efficiently). You can't dismiss science and the scientific method without also dismissing the food you eat, the car you drive, the television you watch, the medicines you take, and the computer you're reading these words on. —Steve Summit (talk) 00:22, 23 April 2007 (UTC)[reply]

Yes I agree with you completely, science has obviously been extremely useful and successful in innumerable ways. It doesn't really help us in any way to question whether it is the only interpretation of reality, but it is rather interesting. :-) Imaninjapirate^{talk to me} 01:02, 23 April 2007 (UTC)[reply]

It doesn't really help us in any way to question whether it is the only interpretation of reality ... such questioning may indeed help, if it enables you to think critically about things you might have otherwise ignored or taken for granted. Such as, for example, 1 + 1 = 2. dr.ef.tymac 09:34, 23 April 2007 (UTC)[reply]

In a way it is, but I think it would be more accurate to call it a group of philosophies. Check out natural philosophy. -- John.Conway 00:34, 23 April 2007 (UTC)[reply]

You are asking about a lot of things. Basically you are asking:

Maths is not based on physical reality but on "axioms".
Works not based on physical reality is a philosophical work.
Science requires Maths in order to function, thus Science is philosophy.
(You did not say this) since Science is philosophy and Religion is philosophy therefore Religion is just as important as Science.

First of all, there is no such thing as a singular Mathematics. Mathematics consists of a collection of diverse mathematical concepts. Some of the mathematical concepts are independent of other mathematical concepts.

Second, mathematical concepts are just like a game. It has rules. The rules are made up by humans. New mathematical concepts are made up all the time.

However, not all mathematical concepts survive into the future. Countless mathematical concepts have been abandon by mathematicians. You do not read or come across these abandon mathematical concepts because they are NOT taught in school.

Instead what you are taught in school/university are those mathematical concepts that have survived the passage of time. Thus these concepts worked and are useful in real life. In short there is evolution in mathematical concepts, they are subjected to natural selection by mathematicians.

That's why maths "works" in real life. Because those mathematical concepts that "did not work" has not survived.

202.168.50.40 01:45, 23 April 2007 (UTC)[reply]

I would like to point out that while it may have been an axiom at one time that 1+1=2, this was actually proved from more primitive axioms by Bertrand Russell and Alfred North Whitehead in Principia Mathematica, published in 1910. --Anonymous, April 23, 2007, 02:16 (UTC).

The difference between philosophy and science is its testability. All scientific hypothesis is testable by definition, including 1+1=2. Philosophy is not defined by it's testability. Theories of God, goodness, utility, etc, are all fundamentally untestable. When philosophy is testable it becomes science, and when science becomes untestable it is philosophy. --Tbeatty 02:50, 23 April 2007 (UTC)[reply]

Well, aren't those things at least partially testable? I mean this in the sense of narrowing down the answers in a multiple-choice problem:

"What is [indiscernible number]+[indiscernible number]?"
a. £ b. cheese c. 4 d. 6

To say that something is discretely "testable" or "untestable" is mistaken. There are degrees of certainty, and in my example problem, it is quite clear that a and b are NOT the correct answers. This can be tested (albeit non-physically) with the following sort of logic:

The solution to the problem is a number. (proved by properties of numbers, in this case closure)
"cheese" is not a number.
Therefore, "cheese" cannot possibly be the solution to the problem.

So the difference between science and philosophy is the method of testing. Philosophical notions, just like scientific theories, are used to explain. But the key here is the testing itself. Philosophy uses pure logic to test its notions, while science uses experimentation. Something like, for instance, a proof of God, can be shown to be false. This is what happened with the Ontological argument. The consensus of contemporary philosophers is that the argument is fallacious. The only difference is that there is much less to test. I personally see nothing different between using a Modus ponens to prove something, or to measure it in a laboratory.--Kirby♥time 10:36, 24 April 2007 (UTC)[reply]

I think the questioner misses the key point about mathematics. It doesn't claim that the axioms are true - it merely states that if you accept the axioms then these other things follow from that acceptance. To take an absolutely classic example of this - all of Euclid's geometry (stuff like "the sum of the angles of a triangle is 180 degrees") is based on a set of axioms - one of which is that parallel lines never meet. Everything he said is true in an place where parallel lines never meet. However, if you draw two "parallel" lines on the surface of a sphere and do all of your geometry on that surface - then parallel lines eventually cross - and Euclid's axioms are untrue - and as a consequence, all of the things that follow from those axioms are open to doubt. Indeed - if you draw a triangle on the surface of a sphere, it's angles don't add up to 180 degrees. This doesn't mean that Euclid was wrong - it means that he's only correct in situations where his axioms are true. Where they aren't true - all bets are off. Mathematics doesn't claim to produce truths about the world - it merely produces conclusions that are dependent on some set of axioms. Indeed, one may pick a set of axioms that are absolutely NOT true in the real universe and mathematics can go to work and produce conclusions about how things would hypothetically be if they where. This is totally different from philosophy. Now, science is a different matter. In science (not mathematics) - you can test the universe using experiments - and use those to specify axioms that are "true" (or at least true to within the limits of your experimental error). Again, this is totally different from philosophy. SteveBaker 15:12, 24 April 2007 (UTC)[reply]

Shark attack

I was wondering if it is possible to rip a shark's gills with your hands, what do ya think?Bastard Soap 22:07, 22 April 2007 (UTC)[reply]

If I was getting attacked by a shark, as a last resort (say if the thing had hold of my leg) I'd probably go for the eyes. --Kurt Shaped Box 22:09, 22 April 2007 (UTC)[reply]

I doubt it. Shark hide is very tough and strong, and a shark small enough to have hide thin enough to rip would also have gills too small to get a good grip on. Anchoress 22:11, 22 April 2007 (UTC)[reply]

Sometimes you just have to ask yourself in these situation "What Would Che Do" (WWCD)? --Kurt Shaped Box 22:30, 22 April 2007 (UTC)[reply]

I've seen a turtle do just that on TV -- kinda doubt a human would have much luck. Vranak

I am sure you're meant to punch them in the nose.137.138.46.155 13:25, 23 April 2007 (UTC)[reply]

I would probably go more for the APS Underwater Assault Rifle [Mαc Δαvιs] ❖ 16:06, 23 April 2007 (UTC)[reply]