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 Posted: Thu Oct 05, 2006 11:39 pm
When I reading a physics book and came across the Second Law of Thermodyamics, which states "The entropy of an isolated system not at equilibrium will tend to increase over time, approaching a maximum value." (Rudolf Clausius). Upon further research of this topic, I found that this is one of the only laws of physics that dosent always apply. An example of such occures when you have a box, where two kinds of particles are seperated and are kept seperate by a barrier (lets just say they can be for the sake of the explination) when you remove the barriar and the particles mix, thus increasing entropy, these partices will continue to move around and mix. Thats not the problem, its the possiblity that they may, however unlikely, be once again completly seperated, which means entropy has decreased, which isnt allowed by the second law.
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Posted: Thu Oct 05, 2006 11:57 pm
As far as I understand it (physics really isn't my thing) since you have removed the barrier, the box 'o particles is no longer a closed system, and thus the second law doesn't apply.
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Posted: Thu Oct 05, 2006 11:58 pm
Jaaten Syric As far as I understand it (physics really isn't my thing) since you have removed the barrier, the box 'o particles is no longer a closed system, and thus the second law doesn't apply. But it's still a box, thus its a closed system from the outside world, right?
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Posted: Fri Oct 06, 2006 12:04 am
But you, an outside force acted on it, bringing energy into the system. There can be other ways around it as well, (mainly because you left state of the particles as undefined...). Things like density can get in the way...If a liquid (or fine-grained solid) is one of the particles in quesion, they may become separated via hydraulic sorting. Now, the particles may be separate again, but not in the same manner they were before (again, outside of the basics required for a study of astronomy physics is not a fiel I can claim indepth knowledge of...)
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Posted: Fri Oct 06, 2006 12:09 am
Darken_mortal Jaaten Syric As far as I understand it (physics really isn't my thing) since you have removed the barrier, the box 'o particles is no longer a closed system, and thus the second law doesn't apply. But it's still a box, thus its a closed system from the outside world, right? Not really. In order to be a closed system the system in question must be unable to exchange energy with its surroundings. The box is able to absorb heat and release it. So it technically isn't closed. I was under the impression that entropy is simply the quantitative measure of the amount of thermal energy required to do work
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Posted: Fri Oct 06, 2006 12:13 am
Oh I should point out, a law in science is merely a very simple and math based description of observations as opposed to a theory which is a more abstract and general description.
The law of gravity simply states that two objects are attracted to one another at an acceleration determined by a certain equation that takes their masses as variables (I don't remember the exact equation)
The theory of gravity is currently the warping of space time by the mass of an object, which causes things to accelerate towards these objects.
See the difference?
The law is not more proven or better. It describes the simple observations and the math. The theory describes the causes.
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Posted: Fri Oct 06, 2006 12:14 am
But left to their own accord, wouldnt two kinds of particles, moving freely in a box eventually, even for less then a second, be in some sort of order?
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Posted: Fri Oct 06, 2006 12:15 am
Darken_mortal But left to their own accord, wouldnt two kinds of particles, moving freely in a box eventually, even for less then a second, be in some sort of order? Remember, entropy is not a measure of order and random chaos. Only the amount of thermal energy available to do work.
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Posted: Fri Oct 06, 2006 12:15 am
well (assuming no outside force continues to act on the box) eventually they would reach equilibrium again, and its entirely possible that they could be divided again a'la density or other effects...
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Posted: Fri Oct 06, 2006 3:37 pm
PoeticVengeance Darken_mortal Jaaten Syric As far as I understand it (physics really isn't my thing) since you have removed the barrier, the box 'o particles is no longer a closed system, and thus the second law doesn't apply. But it's still a box, thus its a closed system from the outside world, right? Not really. In order to be a closed system the system in question must be unable to exchange energy with its surroundings. The box is able to absorb heat and release it. So it technically isn't closed. I was under the impression that entropy is simply the quantitative measure of the amount of thermal energy required to do work Let's assume it's a completely closed system. Entropy is a measurement of the amount of disorder in a system. Now, these particles may be completely separate, but remember, they will move together again. Eventually, the amount of entropy in that system will increase to the maximum value. It doesn't really matter what happens in the middle. Look at it this way: There's a big box of bricks sitting at the side of the road. If I come along and pick this box up and throw it, (I can, because I'm God.) there is a chance that the bricks will assemble themselves into a 2 storey house, with the box sitting neatly in the middle of the living room. Slim chance, but there you go. This system appears to be in perfect order, destroying the third law. Now, suppose I do nothing more to the house. I leave it alone, and nobody ever touches it again. It's now a closed system. Slowly, the box will rot. The bricks will crumble. The system decays into disorder. Eventually, there's a small pile of dust sitting by the road, waiting to be blown away by the wind. This system is now at maximum entropy, and there's not much opportunity to fix it. Voila! <3
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Posted: Sat Oct 07, 2006 11:33 pm
Kuroi Kokoro no Mendori PoeticVengeance Darken_mortal Jaaten Syric As far as I understand it (physics really isn't my thing) since you have removed the barrier, the box 'o particles is no longer a closed system, and thus the second law doesn't apply. But it's still a box, thus its a closed system from the outside world, right? Not really. In order to be a closed system the system in question must be unable to exchange energy with its surroundings. The box is able to absorb heat and release it. So it technically isn't closed. I was under the impression that entropy is simply the quantitative measure of the amount of thermal energy required to do work Let's assume it's a completely closed system. Entropy is a measurement of the amount of disorder in a system. Now, these particles may be completely separate, but remember, they will move together again. Eventually, the amount of entropy in that system will increase to the maximum value. It doesn't really matter what happens in the middle. Look at it this way: There's a big box of bricks sitting at the side of the road. If I come along and pick this box up and throw it, (I can, because I'm God.) there is a chance that the bricks will assemble themselves into a 2 storey house, with the box sitting neatly in the middle of the living room. Slim chance, but there you go. This system appears to be in perfect order, destroying the third law. Now, suppose I do nothing more to the house. I leave it alone, and nobody ever touches it again. It's now a closed system. Slowly, the box will rot. The bricks will crumble. The system decays into disorder. Eventually, there's a small pile of dust sitting by the road, waiting to be blown away by the wind. This system is now at maximum entropy, and there's not much opportunity to fix it. Voila! <3 That makes sense, but isn't it a separate principle from entropy? I was really sure that entropy was the measure of the lack thermal energy remaining within a system to do work
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Posted: Sat Oct 07, 2006 11:48 pm
Darken_mortal When I reading a physics book and came across the Second Law of Thermodyamics, which states "The entropy of an isolated system not at equilibrium will tend to increase over time, approaching a maximum value." (Rudolf Clausius). Upon further research of this topic, I found that this is one of the only laws of physics that dosent always apply. An example of such occures when you have a box, where two kinds of particles are seperated and are kept seperate by a barrier (lets just say they can be for the sake of the explination) when you remove the barriar and the particles mix, thus increasing entropy, these partices will continue to move around and mix. Thats not the problem, its the possiblity that they may, however unlikely, be once again completly seperated, which means entropy has decreased, which isnt allowed by the second law. The problem with this example is that you would have a hard time finding a situation in which the particles in a closed system suddenly come apart. Without an actual example, your proposed situation is basically off the wall, so to speak.
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Posted: Sat Oct 07, 2006 11:51 pm
Kuroi Kokoro no Mendori Look at it this way: There's a big box of bricks sitting at the side of the road. If I come along and pick this box up and throw it, (I can, because I'm God.) there is a chance that the bricks will assemble themselves into a 2 storey house, with the box sitting neatly in the middle of the living room. Slim chance, but there you go. This system appears to be in perfect order, destroying the third law. Now, suppose I do nothing more to the house. I leave it alone, and nobody ever touches it again. It's now a closed system. Slowly, the box will rot. The bricks will crumble. The system decays into disorder. Eventually, there's a small pile of dust sitting by the road, waiting to be blown away by the wind. This system is now at maximum entropy, and there's not much opportunity to fix it. Voila! <3 There is a problem at the begining of your example. You interacted with the closed system by picking it up and throwing it. Also, the way the 2nd law is stated, it implies not that the system in question is not interacting with it's surroundings, but that it can't.
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Posted: Mon Jul 09, 2007 9:55 am
Hum, let me remember my Thermodinamic classes...
The Second Law does apply to your system, it is actually one of the first examples given. But you must always remember entropy is a measure of chaos because it is a measure of microscopic multiplicity. The actual formula is S=kB*ln(Omega) where kB is the Boltzman constant and Omega is the state's multiplicity. For example, if you have a pure cristallin substance at 0K, you only have one conformation possible, Omega equals one and entropy is zero. That is the comparison value used by phisical chemists.
i.e., imagine you have a deck of cards. you pick it and you shuffle the cards. Ok, this is not a 'sistem', but it's an example of one - in your box, the shuffling would be the cinetic energy of the particules. At any given time of the shuffling, your 'system' is at a certain state. You have 52! states avaliable (52 positions to 52 cards). It is possible that your deck will end up perfectly organized by numbers, or by decks.. The chance of that happening, if you did a random shuffling, is of 4/52! and (13!/52!)^4. but if you start thinking of all the dehorganized orders you can end up with, there are...well, I won't do the math, but there are many. And so, the possibility of having a dehorganized deck is greater than that of having an organized deck, and that is why the 'entropy' of a dehorganized state is greater than that of an organized state.
I hope I didn't complicate it too much...
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Posted: Wed Oct 03, 2007 7:24 pm
Heat is the most often used form of energy when referring to entropy because heat is sort of the freest form of energy. Left to it's own devices it will always dissipate. The only way to get it to do otherwise requires more energy input than the amount of heat you "gain."
That and pretty much every form of energy will convert into heat energy when not in a static state (even sound converts to heat.)
As for that box there's zero chance of it returning to zero entropy because entropy takes more things than the positions of particles into account. If the contents of that box are at absolute zero it is very different from a box that is identical (if only or a moment,) except that the contents are at 16,000 degrees Celsius.
Likewise you need to account for any sound waves, static electricity, any photons generated, the velocity vectors of each particle and each atom if the particles are made up of multiple atoms, the angles and energy levels of the electrons of those atoms, any vibrations traveling along the inner surface of the box, etc.
And that's just if the collisions of the particles in the box don't even deform them at all.
Long story short, every time those particles do anything but continue going in the direction they were going a moment ago at the same speed they were going a moment ago some of the energy, in one form or another, is lost to them, forever impossible to reclaim.
Returning to original entropy does not have a very very slim chance of occurring, it has no chance of occurring. If it seems to have returned to it's original state then you've forgotten to keep track of some variable.
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