Wikipedia:Reference desk/Archives/Science/2007 October 24

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1 October 24

[edit] October 24

[edit] Frosty Freezer Food

I've gone to my freezer to heat up a prepackaged frozen entree. And when I take it out of the box, I notice the food beneath the plastic wrap is buried in a heavy coat of ice crystals. Usually there are none. Does that mean this entree had defrosted at the store? Is it safe to eat? What causes frozen foods to develop ice crystals? (like that nasty layer of snow on old ice cream?) --24.249.108.133 00:29, 24 October 2007 (UTC)

It could be condensation from the air when it was frozen. The vapour pressure of water is temperature-dependent, so when the food/container was warmer before packaging, there was more moisture in the air. Once the package was sealed and frozen, that amount of moisture became higher than the decreased vapour pressure at the lower temperature. This causes the "excess" moisture to crystallize out as ice. Your food should be safe; the ice simply means it wasn't packed in a vacuum. 142.103.207.10 01:00, 24 October 2007 (UTC)

You might want to see our article about Freezer burn.

Atlant 12:46, 25 October 2007 (UTC)

[edit] Does the Earth's magnetic field rotate daily w.r.t the solar system?

Obviously, the Earth's rotation must have an effect on the magnetic field, because of the difference between magnetic and axial north, but can we say the field spins with any certainty, assuming that would be well-defined? 217.43.117.117 01:14, 24 October 2007 (UTC)

The earth's magnetic field spins along with the earth. It does slowy drift over the years, so that the magnetic poles shift over the years. The field will affect the space around the earth, out to the distance where the solar wind dominates the magnetic field. Graeme Bartlett 01:40, 24 October 2007 (UTC)

Yeah - 'true North' (as in "the axis of rotation") and 'magnetic North' (the place where the magnetic field lines converge) disagree. As the earth rotates the location of 'magnetic North' stays still relative to the surface of the earth (at least on the scale of days and weeks - it moves slowly on the scale of months and years). Hence, you would be able to measure a daily rotation of the field-lines if you were stationary with respect to the Sun. SteveBaker 04:15, 24 October 2007 (UTC)

Actually, relative to specified location of the Earth's surface, the magnetic pole describes an rough circle with a radius of tens of miles over the course of the day because it is deflected away from the position of the sun due to the magnetic field of the solar wind. Dragons flight 07:06, 24 October 2007 (UTC)

Wow! Interesting. The wobble due to the misalignment of magnetic and rotational poles is around 1000km (and moving by 40km per year right now) - so this adds a few percent to the overall effect. I guess that makes our answer to the OP's question more like: "97% Yes, 3% No". Of course there is this theory that the earth's magnetic field is about to do one of it's major North/South 'flips' any time now. All bets are off if that happens! SteveBaker 14:23, 24 October 2007 (UTC)

[Original poster]: Thanks for the replies guys - very informative. There's still one thing on which I'm not clear, but I didn't express the question very clearly: If magnetic north was identical to axial north then would the magnetic field be spinning with the earth? Do you see what I mean, the effect of the angle between the magnetic and axial poles gives the field a wobble, but apart from that wobble, is it spinning with the earth? The reason I asked if the question was well-defined is that I'm not sure in what way a spinning magnetic field would be differentiable from a non-spinning one. To illustrate, if i had an magnet and put it inside a spherical shell, and simply span the shell without the magnet spinning, would it be possible to determine from outside the shell whether the magnet span with it or not? What if it was an electro-magnet and was attached rigidly to the shell, but now we turn the magnet off, spin the shell a little and then turn it back on. Can we now tell from outside that the magnet has rotated on its axis? In the limit, would continous rotation be any different to this? Perhaps the answer has something to do with the dynamic nature of ferromagnetism... In any case, further ellucidation would be greatly appreciated. 217.43.117.117 01:53, 25 October 2007 (UTC)

Reading magnetic declination, it would seem that the earth's near-surface magnetic field does rotate along with the earth itself, even if such is not explicitly stated (what is stated is that the magnetic declination at any position on the Earth doesn't change much except over a period of years). It's the case that the magnetic field lines in the space around the earth are more oblong on the dark side due to the solar wind. So I would guess that the currents generating the Earth's magnetic field are roughly in sinc with the Earth's rotation, and the major daily influence on it is the solar wind. Someguy1221 02:21, 25 October 2007 (UTC)

[edit] Water, Specifically the acquifer under Pahrump Nevada

I have looked everywhere I can think of for the answer. We bought a home in Pahrump Nevada (Zip Code: 89060)and at the time we were told "The second largest acquifer in America is under Pahrump and stretches from the test site in the north and the Amorgosa valley to under Pahrump.

I was also told that the acquifer is 4755 feet deep, which would be a lot of water!

If you can help me with this problem, I would really appreciate it. I don't know if Wickpedia has ever processed an article on this subject, but I can hope.

Ted Farson (contact information removed to reduce spam) —Preceding unsigned comment added by 12.110.33.171 (talk) 01:25, 24 October 2007 (UTC)

What is your problem, were you misled? Graeme Bartlett 01:43, 24 October 2007 (UTC)

I googled on "pahrump aquifer site:gov" and found this and this (be sure to see the clickable Fig.s). --Milkbreath 03:41, 24 October 2007 (UTC)

[edit] Water content of canned tomatoes

How much water is in one 796ml can of ground tomatoes? Neon Merlin 06:18, 24 October 2007 (UTC)

A tomato could have 95% water, so 756 ml of water. Graeme Bartlett 07:07, 24 October 2007 (UTC)

Yeah, but 95% by volume or 95% by mass? Neon Merlin 17:59, 25 October 2007 (UTC)

What is not water in a tomato is mostly carbohydrate with a density near 1, so the difference between mass or volume is not great, and that 95% is only approximate, so that would accomodate any uncertainty. Graeme Bartlett 00:08, 26 October 2007 (UTC)

[edit] Charge conservation in electrochemical cells

Hi I am trying to show mathematically that the voltage across an electrochemical cell will decay with time. Is this a valid approach? $I = \frac{Q}{t}$ and $V = I R$
--> $V = \frac{Q}{tR}$

Clearly R is a constant, but is Q for particular electrochemical cell? Or should I use $Δ Q$ ? Also does this value of Q or $Δ Q$ change depending on the ratio of concentration of ions in the half cells (according to the Nernst equation initial voltage is the same for the same ratio of product ions and reactant ions)?

My problem comes down to applying the conservation of charge to electrochemical cells. Thanks in Advance

Lots of dupes removed. Lanfear's Bane | t 09:08, 24 October 2007 (UTC)

This slow internet connection is getting annoying. I would've beaten you to the punch if loading didn't take so long. - Mgm|^(talk) 09:14, 24 October 2007 (UTC)

No. It looks like your using a similar method to that used to find find the voltage accross a capacitor. eg see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html for a solution

The electrochemical cell doesn't store electricity as 'charge' - but as changes in the chemistry of the contents..

The usual method to calculate the voltage is to start with the energy change for the process happening eg Fe + Cu2+ >> Fe2+ + Cu Energy change = E (kJ/mol) then divide by the number of atoms to get the energy change per atom (call this X).. Since a charged particle of charge q requires energy X to move through a potential V ie X=qV gives V=X/q (q is the charge released by the reaction)

If X is constant then V is constant - however X can change for various reasons - mostly due to concentration.. (the are models of this - mostly the Nernst equation)87.102.94.157 11:45, 24 October 2007 (UTC)

[edit] Virtual Reality for video games, and resolutions

Is there a limit to how high of a resolution can be displayed in a VR headset? From my understanding, VR headsets have very low resolutions, especially compared to computer monitors or high definition televisions. Also is it possible for VR headsets to replace televisions or monitors for video games? I know it has been tried with some failed attempts (virtual boy, but will it ever catch on? What kind of technological challenges need to be overcome before it becomes a practical technology? 64.236.121.129 14:40, 24 October 2007 (UTC)

The limit is the resolution of the headset itself. Most of the cheap ones use LCD displays of fairly poor resolution (the kind you have in cellphones typically) - and that's the limiting factor. In my last job (Flight Simulation), we had 1600x1200 stereo head-mounted displays - you could buy a REALLY nice sports car (think 'Lamborgini') for the cost of one of them - and they were extremely fragile! The 1280x1024 device is here: [1]. The problem with it 'catching on' is that to do it right is still too expensive and if you do it wrong, people get headaches, nausea, eyestrain, etc. We just need lower cost, higher resolution panels and cheaper optics. The display resolution problem is obvious. The optics problem is 'eye relief' - you can't put a simple pair of screens into some glasses - your eyes don't like focussing down at one or two inches for long periods of time. You need 'collimating' optics to allow them to focus on a virtual image at least half a meter away (preferably more). But it can certainly be done - it's just a matter of cost. SteveBaker 15:38, 24 October 2007 (UTC)

[edit] Body Strength

what is the main compononet that gives the muscle cells its strength and can a compononet be added to make it strong as metal????

Please see the section above where this has already been asked and answered. — Lomn 16:46, 24 October 2007 (UTC)

[edit] can you permanentaly stop PKC (Protein Kinase C) activity in vivo ?

if yes, with what? —Preceding unsigned comment added by Poppynash (talk • contribs) 17:00, 24 October 2007 (UTC)

Kind of. Isoenzyme-specific PKC inhibitors such as Go6976, safingol or rottlerin, and broad-spectrum PKC inhibitors such as bisindolylmaleimide may partially or fully inhibit PCK function in vivo, but only for as long as you continue to provide the inhibitors to the cells of interest. You can't just apply a single dose of inhibitor an expect PKC to stop functioning permanently. That is not possible. Rockpocket 18:31, 24 October 2007 (UTC)

Some Protein kinase C isozymes have been been knocked out using mice as the experimental system[2]. --JWSchmidt 01:24, 25 October 2007 (UTC)

[edit] Time Dilation

Assuming a traveller sets of from the Earth at a constant velocity of half of the speed of light for a round trip of 8 years (as experienced from the Earth's reference frame), would I be correct in saying that the traveller only experiences approximately 6.928 years? --80.229.152.246 21:02, 24 October 2007 (UTC)

Yeah, you got the right answer. A real traveler doing a round trip like that would want to spend a total of on the order of a year doing all the accelerating and decelerating involved, so he doesn't get squished like a bug. Accelerating to half the speed of light in just a day or two is not something you want to do! But special relativity classes tend to just ignore that little detail, and assume that the acceleration duration is a negligible portion of the trip. MrRedact 22:30, 24 October 2007 (UTC)

Er, why would you take longer than a day or two? At constant 9.8m/s^2, you hit the speed of like in about 8.5 hours. --Wirbelwindヴィルヴェルヴィント (talk) 23:05, 24 October 2007 (UTC)

Might want to check your figures there (assuming "like" is a typo for "light"). I think you dropped about three zeroes. Not counting relativistic effects. --Trovatore 00:04, 25 October 2007 (UTC)

Guys - this is not exactly rocket science! v = a.t - so t = v/a - if you want to go at (say) half the speed of light with an accelleration of 1g then you have t = (2.998x10⁸/2)/9.8 seconds which is over fifteen million seconds which is about 177 days. So - yeah - you need six months to get to half the speed of light and another six months to slow down again at a comfy 1g. So MrRedact is exactly right and Wirbelwind needs some more calculator batteries! We are wise to choose half the speed of light because you can pretty much not worry too much about relativistic effects at that speed (for back-of-envelope calculations at least). You can't reach the speed of light no matter what - and even getting reasonably close to it is going to take you an insane amount of time. SteveBaker 01:22, 25 October 2007 (UTC)

I agree with everything Steve says -- except the part where he says "this is not rocket science"! --Anon, 08:04 UTC, October 25, 2007.

Incidentally, the original poster referred to a round trip "at constant velocity", which is impossible if "velocity" is being used as a physicist would to mean a vector quantity. At constant velocity, you can't turn around and come back! But a round trip at constant speed is possible by traveling in a circle, for example. (The half year-or whatever of acceleration would then have taken place before the trip began.)

Sorry, that should be 'a trip of around 8 years'. That's what asking questions when you are far too tired does... --80.229.152.246 11:54, 25 October 2007 (UTC)

For the circular trip to take 8 years at c/2, the circular path must have a circumference of 4 light-years and therefore a radius of 2/π light-years or 6.02×10¹⁵ m. To stay on the circular path therefore requires a continuous thrust (centripetal acceleration) of v²/r = (1.50×10⁸)²/(6.02×10¹⁵) = 3.74 m/s or about 3/8 gee. At least, that's as perceived in our external reference frame; I'm not sure how relativistic effects might change it in the spacecraft's frame. --Anon, 08:07 UTC, October 25, 2007.

[edit] Strong Force vs. Electromagnetic Force

How close do 2 protons have to be for the Strong Force to overcome the repulsion of the Electromagnetic Force? Sappysap 18:18, 24 October 2007 (UTC)

It never does. Luckily for us. If Helium-2 were a bound state, all the stars would explode. --Trovatore 18:33, 24 October 2007 (UTC)

Wow! Diprotons, thank you for telling me about them. One follow-up fantastical question if no one minds :) Can an analogy be made between nuclei, which attract at short distances and repulse at long distances, and matter in general which attracts at short distances (say within the range of a galaxy) but seems to repulse at long distances (galaxies are all moving away from each other)? Perhaps the large scale acceleration of galaxies isn't due just to the momentum from the Big Bang. I'll gladly share a Nobel Prize in Physics for any helpful consideration! Sappysap 18:51, 24 October 2007 (UTC)

The movement of galaxies away from one another over long distances is not do to any repulsive force between them, but merely to the expansion of the universe, which only overtakes gravity at long distances. Someguy1221 19:36, 24 October 2007 (UTC)

[edit] Possible to generate a magnetic field to repel bullets?

Is it possible? —Preceding unsigned comment added by 64.236.121.129 (talk) 19:31, 24 October 2007 (UTC)

Well, if theyre made from iron, maybe. The earth has such a shield - the magnetosphere - which, according to our article Van Allen Belt is equivalent to 1 millimetre of lead. (That number of course applies to charged particles, not uncharged bullets, so we can be off "by a long shot", but it should give you an idea of the magnetudes (sorry about the silly pun) involved.) — Sebastian 19:46, 24 October 2007 (UTC)

However, since bullets aren't made from iron or other ferromagnetic materials (they're primarily lead, often with a copper jacket), the short answer to the question is "no". Bullets are not magnetic, and so cannot be repelled by a magnetic field. — Lomn 19:51, 24 October 2007 (UTC)

That's not quite right - a non-ferromagnetic conductor moving in a magnetic field will have a current induced in it - and hence become an electromagnet - and could be deflected.. I still imagine that in practice the answer is no - the magnetic generation apparatus would be massive - the best way to utilise it therefor would be to hide behind it!87.102.94.157 19:57, 24 October 2007 (UTC)

What if, the generation device was powered by some kind of advanced Micropower, along with other advanced technologies. Hypothetically, with advanced technology, is it scientifically possible? 64.236.121.129 20:10, 24 October 2007 (UTC)

If we're going to jump that far, why even bother with magnetism? We might as well jump to science fantasy and invent some Treknobabble about reversing the polarity to stop the bullet. In that case, sure. But I'll stick with "no" for my answer. A magnetic field will not stop a bullet. — Lomn 20:47, 24 October 2007 (UTC)

Because we know magnetism exists, and micropower, is also an area of scientific research. "Trecknobabble" as you put it, doesn't and isn't. 64.236.121.129 20:56, 24 October 2007 (UTC)

Magnetism exists -- but there's no reason to expect it to have any effect. Micropower is just a power source, providing the same power as any other power source, and a particularly ill-suited one. Thirdly, your (first) post throws out unspecified "advanced technologies". So you're asking hypothetically, with a theorized power source of dubious merit, using other things that aren't even articulated (much less things that exist), can we use a force that doesn't have a relevant effect to do what we want?" I could say that cold fusion could amplify the strong nuclear force of tissue paper to stop bullets and be just as scientifically useful. — Lomn 21:15, 24 October 2007 (UTC)

An electro magnetic field would affect the movement of bullets. I think 87.102 already pointed that out to you. I don't think the OP was asking you, but he's asking if a powerful electro magnetic field would stop bullets. I think he just added "advanced technology" to mean making the power source small, and extremely powerful. The answer is yes, with enough energy, an electro magnetic field can. Also I must remind you to be civil, and helpful. No need to be condescending with words like "trecknobabble". It's not very helpful, and only serves to ridicule the question. Malamockq 02:59, 25 October 2007 (UTC)

Lomn's mad haha. Anyway I think we already established that a magnetic field would affect a bullet. That's relevant. I'm not sure you have the proper education in this field to answer my question. 64.236.121.129 13:44, 25 October 2007 (UTC)

I feel that it's extremely important on the science reference desk that answers remain grounded in science. With sufficient unfounded assumptions, we can answer "yes" to any "is x possible" question and not do any of them justice. Rather, I find that "is x possible?" needs a healthy dose of "is it possible now or in the near future, with equipment appropriate to the application, etc, etc". It's important to point out to people, then, that "magnetism exists" says nothing about whether it's applicable and that "micropower" is irrelevant in a macropower application. Further, I dispute your allegation that treknobabble is condescending. In fact, I find it a quite precise description of the "solution" presented above. As for "mad" -- not really, though I'm disappointed when hand-waving is seen as a valid method of problem-solving. — Lomn 13:47, 25 October 2007 (UTC)

Well I was just curious if it could ever be made in the future. Of course I know it can't be made now because if we could, then we would have them! No need to explain why it can't be made now because I already know why. I mentioned micropower for obvious reasons. This kind of technology would be most useful on a soldier, you would need some kind of small power source, that's still powerful. Incorporated into a powered exoskeleton perhaps. If you are going to participate in the discussion, it would be nice if you at least concede that magnetism/electro magnetism does affect the movement of bullets. 64.236.121.129 15:43, 25 October 2007 (UTC)

Lead conducts electricity right? Couldn't the kinetic energy in the bullet be converted to electrical energy and get dissipated in internal resistance inside the bullet? 64.236.121.129 20:04, 24 October 2007 (UTC)

Not really. While moving through a magnetic field perpendicular to the bullet's direction of motion, a voltage will be induced across the bullet. However, once the maximum voltage is reached, electron flow stops, and the magnetic force on the electrons in the bullet will still equal that on the protons, and so there will be no net magnetic force on the bullet. Now, since all materials have at least some diamagnetic character, you could try to repell the bullet in this manner. However, it generally takes the most powerful sustainable magnetic fields to simply counteract gravity using diamagnetism, so good luck deflecting a moving bullet with it. Someguy1221 20:18, 24 October 2007 (UTC)

The voltage induced will cause a current eddy current might be useful here - it's possible that using a field strong enough to deflect a bullet would induce such a current that the bullet (lead) is melted due to resistance heating - so now you'd be hit by moltenlead . no good.87.102.94.16 12:47, 25 October 2007 (UTC)

If it were to turn to molten lead, it might not be as bad at all. The bullet would lose most of its armor penetrating ability. Combined with ceramics, kevlar, heat resistant materials, or better, a powered exo skeleton, it would work. 64.236.121.129 16:09, 26 October 2007 (UTC)

An interesting point, since "just use kevlar" is of course the trivial answer to this problem. Since you're absolutely convinced that this must be possible, though, in light of all the problems, what-ifs, maybes, and inaccuracies riddling this discussion -- why even ask in the first place? It seems you've had your mind made up from the beginning. — Lomn 17:38, 26 October 2007 (UTC)

Kevlar can't protect against armor piercing rounds or rounds fired from an assault rifle or similar weapon. If this magnetic field really did melt the bullet before it hits, the kevlar would protect against it even if it was an armor piercing round. Malamockq 00:48, 30 October 2007 (UTC)

"Ribbit"

If you could diamagnetically accelerate a frog with sufficient velocity towards the bullet, it would stop it. --Sean 21:22, 24 October 2007 (UTC)

Perhaps you should use Electromagnetic radiation to zap the bullet with so much energy that it evaperates before it strikes you — a laser ray gun should do the job, but it will have to be very high power to deliver enough punch! Graeme Bartlett 06:09, 25 October 2007 (UTC)

Since the OP doesn't like my "no" answer, here's the alternate thought problem: suppose you've found a way to repel a bullet with a magnetic field. What happens to all other matter in the vicinity? If you can stop a bullet speeding towards a soldier, what happens to the soldier's rifle and ammunition (or hell, his dog tags?) What happens to his arm as soon as he moves it? It's diamagnetic, too. So here you go: once you solve the utterly impractical problems of stopping a bullet with a magnetic field, you've generated the parallel problems of stopping everything else, too. — Lomn 14:00, 25 October 2007 (UTC)

Uhh, we aren't talking about using diamagnetism to deflect bullets. 64.236.121.129 15:49, 25 October 2007 (UTC)

As best I can tell, that's the only form of magnetism relevant to a copper-jacketed lead bullet. — Lomn 16:31, 25 October 2007 (UTC)

Electro magnetism. 64.236.121.129 17:15, 25 October 2007 (UTC)

That's not really an answer. Materials are ferromagnetic, paramagnetic, or diamagnetic. An electromagnet is presumably what would generate the bullet-stopping magnetic field, but it still has to act on a diamagnetic material -- which is to say, it hardly acts at all. Throw in the loopy-high power requirements (a man-portable nuclear reactor?), posit the room-temperature superconductors that are probably required, consider that the bullet has a high energy to mass ratio (remembering that you have to dissipate the energy while using the mass as your base of magnetic force -- this is far more difficult than, say, levitating a stationary bullet), and by the time you've got something that can stop a bullet, you've got untold other side effects that make the entire exercise moot. — Lomn 18:09, 25 October 2007 (UTC)

Now, I could be wrong on the details, but I just recalled a physics lecture I attended in which the professor swung a pendulum (I think it was copper, could be wrong) through a powerful magnetic field (don't remember if it was static or dynamic), upon which the pendulum stopped essentially instantly. Does an experiment like this sound familiar to anyone? Someguy1221 18:56, 25 October 2007 (UTC)

It sounds like he was using the pendulum as the coil of a generator. In that case, the pendulum is set up to efficiently turn its kinetic energy into electrical energy upon encountering a strong magnetic field. --Carnildo 22:52, 25 October 2007 (UTC)

Yea, that sounds awfully familiar to a post I made earlier. I said a bullet would have its kinetic energy turned into electrical energy if it went through a magnetic field, to which Someguy1221 said it wouldn't. Hah. 64.236.121.129 13:05, 26 October 2007 (UTC)

No, it won't. A bullet travelling through a magnetic field is an open-circuit generator, and won't produce significant amounts of electricity. The pendulum is probably set up as a short-circuit generator, which is very effective at turning kinetic energy into electricity, and from there into heat. --Carnildo 22:00, 26 October 2007 (UTC)

Not to mention your opponent is probably going to use his/her portable nuclear reactor to power an energy gun or something else for his/her robot making your 'bullet stoppind magnetic field' particularly useless. Nil Einne 19:23, 25 October 2007 (UTC)

Ho ho! But we are talking about stopping bullets! We aren't talking about directed energy weapons. If anything, a device that could stop bullets would spur weapons development in that direction, certainly. But we are just talking about if it can be done. 64.236.121.129 20:43, 25 October 2007 (UTC)

I think the most important idea to keep in mind here is that, very simply, any simple magnetic field capable of stopping a non-magnetic object like a bullet would also put significant force on just about anything else passing through it (see the frog, above), which would make this a somewhat impractical method of bullet proofing yourself. Someguy1221 20:53, 25 October 2007 (UTC)

Again, we aren't talking about using diamagnetism, but in all fairness, if you did have a device that powerful, it would be useful for spacecraft. 64.236.121.129 13:09, 26 October 2007 (UTC)

Any extermely powerful magnetic field would set up an eddy current in the bullet as it moves into the field. This will produce a force opposing entry. With Newton's 3rd law the force will also appear on the magnet. I have seen Someguy1221's metal being severly slowed down by a magnetic field. WIth a strong static magnet with poles close together, moving an aluminium plate inf the field was like moving it through honey, the faster it moved the more the resistance. Graeme Bartlett 00:24, 26 October 2007 (UTC)

So if you fired a bullet at a powerful magnetic field, the bullet would slow down then fall harmlessly despite it being diamagnetic? 64.236.121.129 12:57, 26 October 2007 (UTC)

[edit] Geeky TV

Do you guys just love Big Bang Theory? Like you've been waiting for this show you're entire lives, right? Beekone 20:45, 24 October 2007 (UTC)

Utter, utter, utter, utter', CRAP. Proper science geeks like: (a) Top Gear, (b) Mythbusters, (c) Junkyard-Wars/Scrapheap-Challenge (before they screwed it up in the last couple of series). SteveBaker 20:51, 24 October 2007 (UTC)

and look around you for a laugh. Theresa Knott | The otter sank 22:43, 24 October 2007 (UTC)

Right - I "lost it" at "H twenty" - hydnjo talk 00:57, 25 October 2007 (UTC)

"Germs originated from Germany, before spreading rapidly to the rest of the world" RHB - Talk 22:51, 24 October 2007 (UTC)

I lost it at the 1000 degree boiling point, then the hand reaches in and just grabs the egg out of the water XD --⁪ffroth 21:57, 26 October 2007 (UTC)

OMG those are funny! I had the best laugh today watching the Maths episode than I've had in many months. I was laughing uncontrollably with tears in my eyes for several minutes, triggered by the absurdity of the first story problem. MrRedact 07:12, 25 October 2007 (UTC)

Top gear? I assume you mean the BBC car show. That's not science, that's everyday technology. No, it isn't even that - the little I have seen of it is not abut the innards of a car, but about how fast it accelerates and how it looks. Yawn. Instead, try World Solar Challenge, a current event, or DARPA Grand Challenge, the next edition of which will be in just over a week, on 3 November. Especially the latter is so much at the forefront of technology that science geeks can't help but be thrilled. And it's bound to be shown at a tv set near you. On top of that, it's about something that could help save the planet ("Oh, Flash, I love you. And we only have a few years left to save the Earth!"). DirkvdM 07:17, 25 October 2007 (UTC)

Am I the only one who thinks that Mythbusters is pretty horrible? Their complete disregard of anything resembling the scientific method, or even basic logical thought anger me to no end. Their typical method is "1)Perform experiment with so many uncontrolled variables that it doesn't come close to proving or disproving anything. 2) If step 1 didn't involve blowing something up, modify the experiment so that something blows up and perform it again. 3) Smugly announce that the myth is 'busted'.69.95.50.15 15:56, 25 October 2007 (UTC)

I got to tell you, I'm a little surprised. Science baffles me to no end, but I think Big Bang Theory is hilarious. If I was a physicist I imagine that would be an accurate portrayal of my life, or if I had a friend who was a geeky scientist I think that's what they would be like. Emphasis for hilarity aside, you got to admit some of their geeky quirks are right on. Right? A little? Beekone 16:02, 25 October 2007 (UTC)

I agree with you about Mythbusters, particularly because they often claim that they're using science. Really, they're all just special effects geeks for hollywood. -- JSBillings 13:33, 26 October 2007 (UTC)

Of course it isn't actual, write-a-paper-publish-in-a-journal kind of science. The point is that they do actually test these myths. Very often with mythbusters, when they announce the myth, I sit up and think "hey yea, I wonder if that's true". And usually they do provide an answer, and usually it's the best answer that you're ever going to get. Real science just can't or won't answer most of these questions. They're not being completely scientific, but they're mimicking the scientific method, to provide enough insight into the question, for me to be satisfied. So it's not just about doing random cool stuff, like so many of these 'cool science' shows. Most of the value comes from the answers that they get. risk 13:45, 26 October 2007 (UTC)

It's not full on hard-core science - but it has a lot of the basics right - they usually have controls for their experiments and they measure things. They make a lot of mistakes and assumptions too - and some of the things they do are clearly flat out wrong. But it has the desired effect of being entertaining and making you think. (Even if it's only "Ooohhh - they got that wrong because they forgot to allow for such-and-such.") If you actually watch the show, they very often use the "PLAUSIBLE" conclusion when something seems true but may not be. They pretty much only use "CONFIRMED" if they managed to reproduce something AND they discovered documentary evidence that it actually happened as described. But some things they are definitely able to bust - conclusively. The old story that if you throw a penny off the top of the empire state building it'll crack the concrete when it hits the ground. They build a miniature wind tunnel - they use it to measure the terminal velocity of a penny - then they make a gun that can fire a penny at speeds well in advance of it's terminal velocity - then they fire pennies at a concrete paving slab of the same kind as the ones used in New York - and the concrete doesn't break. They ramp the speed up and up and they still can't break it even at speeds far in excess of the terminal velocity of a penny. Then (here is the dubious bit) they make a dummy head (yeah - right) and shoot the penny at that and nothing much happens. I don't buy the idea that an old, dried out human skull embedded in ballistics gel necessarily fractures at the same impact loading as a real human skull which is still alive, immersed in fluids and containing a brain. But this test simply gives them the confidence to shoot the penny at each other - and the skin isn't even broken. That's a pretty conclusive "MYTH BUSTED" that it would difficult for a hard scientist to argue with. I feel better off knowing that this is urban legend. Other things they do are much, much worse. Their reliance on the "fact" that ballistics gel mimics all sorts of properties of a human body or that the wooden limbs on 'Buster' the crash test dummy will in fact break when a human limb would break...Nah - nonsense. But some things are genuinely clever and the results are FAR from obvious. SteveBaker 20:16, 26 October 2007 (UTC)

Of course it's pretty obvious that a penny, being a flat piece of metal (not a sphere), would never reach a high enough terminal velocity to do much damage. The idea of having one drop on my head is a different matter, though. But I suppose even that would indeed be safe. This reminds me of when my brother was on top of the Pisa tower he couldn't resist the temptation to 'play Galilei' and drop an orange. When he was back down and inspected the 'drop zone' he found that it had drilled a distinct hole in the ground. Size is nothing. Round is everything. Or pointy, of course. I wonder what a dart would have done. DirkvdM 17:37, 27 October 2007 (UTC)

[edit] How do enzymes evolve?

When I asked my Biology teacher, he fobbed me off with "lots of proteins are created, the beneficial enzymes are the only ones that survive further i.e. survival of the fittest except enzymes aren't alive." Our FA on enzymes mentions little on the subject. Is there any proper, researched mechanism for their evolution? Thanks, RHB - Talk 22:47, 24 October 2007 (UTC)

Beneficial is very vague. What's beneficial for one species could be death for another. bibliomaniac 15 A straw poll on straw polls 23:10, 24 October 2007 (UTC)

Which of course suggests that organisms which create proteins that kill themselves off are not going to be the fittest. Which illustrates well, of course, the idea that the enzymes are not what is being selected for—its the protein creation by the organism. --24.147.86.187 23:22, 24 October 2007 (UTC)

Your teacher is more or less correct. Enzymes don't evolve. They function like little tools in the cell, so your question is like asking how hammers evolve. But the DNA that gives instructions for how to make an enzyme is subject to random mutations. If that piece of DNA does mutate, then the resulting enzyme may work better, or worse, or show no functional change. If the change makes the enzyme work better, let's say faster or use less energy, then the cell stays alive and that change is passed on to future generations: a different enzyme structure than before. But usually the change makes the enzyme work worse and the cell dies. Delmlsfan 23:27, 24 October 2007 (UTC)

Wikipedia has Molecular evolution. --JWSchmidt 00:12, 25 October 2007 (UTC)

Enzymes don't evolve (indeed, they're not alive), organisms that produce the enzymes evolve, and the ones that produce the right enzymes are the ones that survive, to put it simply. Or do you mean to ask how the first enzymes came about? One theory is that they are being made in certain areas of space (forgot the details) and that some of those landed on Earth and kick-started the evolution of life. I am surprised there is nothing on this in the enzyme and protein articles. At least, I can't find it. DirkvdM 08:06, 25 October 2007 (UTC)

One thing about the phrase "enzymes don't evolve." This may be more semantics than anything. We freely talk about how organs evolve, so why not enzymes themselves? When we talk about wing evolution, for example, we don't need to acknowledge that a wing by itself is alive. We're really talking about the evolution of the genes that are responsible for the wing formation. Same thing with enzymes. While enzymes are non-living, we can talk about how enzymes evolve because we're referring to the evolution of the genes coding for the enzymes. In fact, I did a quick search at pubmed and found that researchers use the term enzyme evolution liberally. 128.163.196.164 17:06, 29 October 2007 (UTC)

A minor quibble—generally when astrobiologists talk about getting the molecules of life from space, they usually mean stuff that's a lot simpler than full-sized proteins. Radio astronomers have detected enormous quantities of a number of small carbon-containing compounds that could be building blocks for biomolecules—simple alcohols like ethanol, and even amino acids like glycine. If the Solar System passed through such a cloud at some point, it could have gotten a nice dose of bioavailable carbon. Another model suggests that life got a helping hand from carbon-containing meteorites (see carbonaceous chondrite). Representing perhaps 5% of all meteorites, these guys are loaded with carbon compounds, again including some of the small molecules of life.

For a discussion of the arrival of more complex 'life from space', you'll want to look at our article on panspermia. Setting aside the flakier bits, the scientific kernel is that life on Earth could have originated on other planets (and possibly in other solar systems). During a powerful meteorite strike, fresh material from the planet's surface can be blown back into space; this material will drift until it hits something else (small meteorites from Mars regularly land on Earth, for example). For small particles, it's possible – at least theoretically – for the solar wind to drive material out of the solar system altogether and into interstellar space. In principle, it's possible that such a particle escaped from another planet billions of years ago, and seeded life on Earth. Inconveniently, however, it still leaves us with the question of where did that life come from.... TenOfAllTrades(talk) 14:00, 26 October 2007 (UTC)

What kind of mechanisms are you specifically wondering about? Because any kind of mutation in a gene will result in a mutant form of an enzyme--after all, DNA codes for enzymes. The basic mutations/recombinations you learn about in genetics-- insertions, deletions, translocations, duplications, etc. all provide the possibility for new and different enzymes to evolve. 128.163.224.198 16:00, 29 October 2007 (UTC)

[edit] Size limit of the human body

I remember reading somewhere that there's a theoretical limit to how large we can become evolutionarily speaking due to the fact that as we get larger our weight increases volumetrically but bone strength only increases in cross-section so eventually our skeletons would be unable to support our bodies. Anyone know what the limit might be? Exxolon 23:08, 24 October 2007 (UTC)

Wikipedia has Robert Wadlow, "the tallest person in medical history for whom there is irrefutable evidence". --JWSchmidt 00:03, 25 October 2007 (UTC)

I remember hearing about a much lower limit when falling on you're face becomes potentially lethal. That limit wasn't much larger than our current size. — Daniel 02:57, 25 October 2007 (UTC)

You say "we" and "human body" as if you're talking about humans, but "evolutionarily speaking" as if you're talking about some future species that might be descended from humans but would not be called human. In the latter case, there is much more scope for growth despite the square-cube law by evolving thicker limbs the way hippos and elephants have. The limit in that direction must be at least as large as the largest land animals that have ever lived, i.e. the larger dinosaurs. You could even imagine a being with dinosaur-strength legs but in great numbers like a millipede. I can't imagine any circumstances where that sort of body would be advantageous for an intelligent being (for one thing, the food requirements would be immense!), but it would be physically possible.

On the other hand, if you're talking about beings we would recognize as human, then the limit is set by how far we could evolve in the direction of thicker bones and stronger muscles and still be recognized as human. That is, it's basically arbitrary. --Anonymous, 08:18 UTC, October 25, 2007.

After edit conflict:

Right, that's what I thought too. Our walking on our hind legs makes us rather different from other animals that got to be very big. But of course we could evolve back to four-footers (for whatever 'reason'). In which case I don't see what would stop us from becoming as big as dinosaurs. Btw, do you mean big or tall - weight or length? DirkvdM 08:22, 25 October 2007 (UTC)

A different solution would of course be to go another step 'back' in evolution and enter the water again. Whales are the largest animals that ever lived. And they are supposed to be fairly intelligent, so maybe it wouldn't be such a stupid thing to do. :) DirkvdM 08:25, 25 October 2007 (UTC)

There is no limit speaking in terms of evolution. If an Argentinasaurus can evolve from a macro molecule, then it's possible for human to evolve into an animal that's extremely tall too, but I can't imagine how it could possibly happen with natural or artificial selection. Nothing favors a tall human. The taller you are, the more health problems you have. They aren't better in combat/war, so they don't make better soldiers. They may have some physical advantages (Bubba can make for a good construction worker), but social trends show that humans are using less of their bodies, and spending more time just sitting around doing things that require brain power, rather that physical power (that includes watching TV or playing videogames). And Mr. Brainiac can just build a powerful robot that's stronger than Bubba anyway so it makes for a better construction worker, so who needs Bubba? 64.236.121.129 16:09, 25 October 2007 (UTC)

We also have to consider the effect of the square-cube law in relation to lung capacity. If you maintain the same density, then as you increase the human size further up the scale, the body mass (the cells of which must be oxygenated or die) increases as the cube of the multiplier, but the surface area of the lungs increases only as the square of the multiplier. Eventually you reach a point where the lungs must either undergo an evolutionary change to become more efficient (and thus able to oxygenate the increased mass) or else be unable to support the oxygenation needs of the larger body. Even before that point is reached, the relative effeciency of the lungs would decrease so much that the larger-scaled human would be at a survival disadvantage, with that disadvantage becoming more and more pronounced until the lungs fail to support life functions. 152.16.188.107 02:48, 26 October 2007 (UTC)

Isn't it usually herbivores that achieve the largest sizes? They don't spend quite as much energy as carnivores. They just trot along grazing and use their body size to repel carnivores. SO maybe if we all became vegetarians ... . Another thing is that humans (and other animals) might get bigger if there is more oxygen in the air. I know that is the reason that in somewhere in the past insects (which have very inefficient 'lungs') managed to get very big. DirkvdM 06:58, 26 October 2007 (UTC)

Insects in the past were bigger than they are now - but I don't think that they were ever huge as far as huge things go. Birds have much more efficient lungs than humans, so I suppose that the potential is there for them to become gigantic if flight is abandoned, as demonstrated by the ostrich, moa, terror bird, etc. --Kurt Shaped Box 09:23, 26 October 2007 (UTC)

Gigantic insects were around at the time when there was a lot more oxygen in the atmosphere. Since they absorb oxygen by diffusion through spiracles, a small increase in the partial pressure of oxygen allows a large increase in body size. SteveBaker 19:53, 26 October 2007 (UTC)

Some other factors that limit the size of land animals are circulatory and nervous systems. A single heart eventually can't manage to pump blood quickly enough, so other strategies are needed, like muscle contractions along veins and arteries, combined with one-way valves (and a slower metabolic rate). The nervous system becomes too slow eventually, so more distributed control is needed. We already have reflex actions, which don't need to be processed by the brain. More such distributed reflex action would be needed in a huge land animal, say to control walking and balance. StuRat 20:46, 28 October 2007 (UTC)

About that last bit, it would likely be a very slow animal, so that doesn't seem necessary. And it would probably develop very big feet for stability. Actually, it could probably not lie down to sleep, so the legs would have to 'lock' for that. Of course that would have to be taken to the extreme for a bipedal animal like a human (if we can still call it that). DirkvdM 07:29, 29 October 2007 (UTC)

[edit] Honey

I bought some honey, the kind that comes in a plastic bear, and now that it's down to the last quarter or so of the bear I've noticed that the remaining honey is extremely grainy and thick, even to the point where it's a struggle to squeeze it out. Also, the honey is now a different, lighter, color than when I first got it. Was wondering if anyone knew why this might be? Thanks. 38.112.225.84 23:12, 24 October 2007 (UTC)

Sounds like it's crystallizing (probably various sugars that were dissolved in the liquid). DMacks 23:45, 24 October 2007 (UTC)

If you set the bear in a pan of hot water the honey will go back to normal. --Milkbreath 23:52, 24 October 2007 (UTC)

Bear? What bear?

I also assume it's crystallisation, but isn't that caused by drying out? So how would heating it help? And would it remain uncrystallised after it has cooled down again? DirkvdM 08:30, 25 October 2007 (UTC)

Here is a picture of the bear. But I don't know why honey gets fluid again when it's warmed. Lova Falk 09:00, 25 October 2007 (UTC)

The sugar that has crystallised redissolves when warmed. There's a more scientific explanation for why this happens if you ask...87.102.94.16 12:42, 25 October 2007 (UTC)

I know enough science to know that if you don't use mathematics you're talking crap, but I don't mind talking it. I wonder if there's a userbox for proficiency in crap. Honey is a supersaturated solution of sugar in water. If there is nowhere for a crystal to get started, that is, the inside of the container is smooth, it will sit like that a pretty long time, but eventually a crystal will get started and the jig is up. That's how you make rock candy. If you heat the solution the water can hold more sugar in solution, and the crystals redissolve. --Milkbreath 13:05, 25 October 2007 (UTC)

87.102, I thought by posting my question on the Science desk I was asking...:) Thanks for the answer/links Milkbreath, worked like a charm. As to a userbox for proficiency in crap, I believe that

BA	This user has a Bachelor of Arts degree.

would work in a pinch. 38.112.225.84 14:35, 25 October 2007 (UTC)