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Energy conversion

  1. Apr 22, 2010 #1
    When a helium balloon rises from rest, it gains Ep, at the same time, it gains Ek. So where does these energy come from?
    My guess would be due to density differential, the balloon will rise and this will displace the air molecules which will fall to take the place of the balloon. This reduction of Ep of air molecules is converted to Ek, which pushes the balloon, causing work done on the balloon, thus giving it energy.
    What do you think?
  2. jcsd
  3. Apr 22, 2010 #2


    Staff: Mentor

    You are exactly correct.
  4. Apr 22, 2010 #3
    Thank you for the fast reply :D
  5. Apr 22, 2010 #4


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    Do you mean that a helium balloon gains Ep on ascent... No.

    A helium balloon looses Ep during it's ascent and gains altitude.

    E.g. By pulling a balloon down you expend energy while the balloon gains that energy as Ep.
  6. Apr 22, 2010 #5


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    Science Advisor
    Gold Member
    2017 Award

    The balloon (treated in isolation) gains Gravitational Potential Energy - because it's higher - but the total system - including the air around it, loses Ep, for the reason given above.
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