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Homework Help: Air Molecules and Gravity

  1. Aug 21, 2008 #1
    1. The problem statement, all variables and given/known data
    a. On our planet, all air molecules are attracted by gravity. They should all gather closest to the earth's surface. They don't. Why?
    b. Draw pictures of molecule distribution in a planet with very low gravity, and one with very high gravity.

    2. Relevant equations

    3. The attempt at a solution
    a. The air molecules do not all gather closest to the earth's surface because there is so much room for htem to move around in. Gravity is constant on earth, so they travel all over.

    -I was told this was wrong-

    The picture I drew, I will try to explain.

    o o o o o
    o o o o o
    (they are spread out and all over)

    (they are close together and close to the surface)
  2. jcsd
  3. Aug 22, 2008 #2


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    Homework Helper

    For the first question, the answer to this is the same as the explanation as to why heavy and light gases do not neatly coalesce in 2 separate layers when introduced into a container.

    For the 2nd, give a little more thought as to how the question is phrased. There is a planet with very low gravity and very high gravity. You might want to check out the atmospheres of some of the planets in our solar system (online of course, not literally).
  4. Aug 23, 2008 #3


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    Suppose, just to keep this simple, the entire atmosphere is at one temperature. Do all molecules in a population at the same temperature has the same velocity? What does that mean concerning where they can go, even when the level of gravity is constant?
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