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Perpetual Motion?

  1. Jan 7, 2005 #1
    Perpetual motion has been deemed "impossible", at least in the world we live in. Why aren't the perfectly elastic collisions between gas particles considered perpetual motion?
  2. jcsd
  3. Jan 7, 2005 #2


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    Staff: Mentor

    There are several different characterizations of "perpetual motion" and the one you picked is physically real. There are plenty of similar examples, like a planet in orbit or a particle in motion in space.

    What is impossible are perpetual motion machines - self-powering devices that never need fuel and give off excess energy.
  4. Jan 8, 2005 #3
    Yes, you would violate the 2nd Law of Thermodynamics. Elastic collisions happen, but to control them for energy harnessing purposes...that would require inelastic processes, I suppose.
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