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Old Nov 29th 2014, 04:17 PM   #1
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Question Do gasses in gravity generate thermal gradients?

I know hot air will rise above cooler air, but will you get the same effect even when all of the air is the same temperature and there's no outside source of energy? It seems like, just by random motion, there will temporarily be small pockets of warmer air that would then rise. There would be a cumulative effect creating the gradient. But that would violate the second law of thermodynamics, so what am I missing?
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Old Dec 1st 2014, 04:30 AM   #2
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While at first sight, randomly occurring pockets of warmer or cooler air would naturally differentiate due to buoyancy; there are practical reasons why it would not happen this way.

Any random temperature differences will be small.
Thus the buoyancy effects will be small and any resultant motion will be slow.
The clincher is that direct thermal conduction will even out any random temperature pockets much quicker than convection will move them apart.
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