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Energy spent on holding a kg

  1. Nov 2, 2011 #1
    hello,
    If I hold 1kilogram at one meter of the groud during an hour, what would be the theoretical energy I am spending (in joules for example)?

    Thank you,
    Jaimie
     
  2. jcsd
  3. Nov 2, 2011 #2

    cepheid

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    Staff Emeritus
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    You're not doing any work because the displacement of the object is 0.

    However, your muscles, as a biological system, are inefficient. To just bear a load without moving it, they must alternately contract and relax rapidly. As a result, your body expends chemical energy and you do end up feeling tired.
     
  4. Nov 2, 2011 #3
    Indeed. And as a result, the amount of energy expended depends more on your muscle tone, circulation, metabolism, etc. then on simple physics of the weight and gravity. Place the same kilogram on a solid table for an hour and it becomes obvious that no energy is being expended (the table does not run down its batteries/use up its fuel, etc.)
     
  5. Nov 2, 2011 #4
    I agree with you but when a helicopter holds a weight it is using energy to compense the gravity force, isn't it?
     
  6. Nov 2, 2011 #5

    cjl

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    Yes, because once again, it is inefficient. A helium balloon can hold a weight as well, and it would require no energy input to do so.
     
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