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Does a Hotter Air Molecule Really Rise?

  1. Jul 20, 2004 #1
    This is a thought experiment question.

    I have three air molecules. Two have the same speed. The third is faster than the other two. When they slam against each other, they keep their previous speed after the rebounding acceleration. I put them in a container. I hold them from wanting to move so I can stack them one atop the other. I stack them with the faster air molecule in the middle. Then I let them go. They only bounce along the vertical axis, from the ceiling to the floor of the container. They do not change velocity into the horizontal or Z cordinate, so they always stay stacked vertically, but still bouncing.

    After equilibrium, does the full length of the faster molecule's path have ends equal distance from ceiling to floor or is the top path end closer to ceiling or is the bottom path end closer to floor? And why?
  2. jcsd
  3. Jul 20, 2004 #2


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    Staff: Mentor

    Air is a mixture of different gases and temperature is the average kinetic energy of a large number of molecules. Therefore, the question isn't worded all that well. But the answer is, yes, since gravity still affects the trajectory of a moving molecule, slower moving ones will tend to stay closer to the bottom than a faster moving one.
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