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Work done for stationary object

  1. Dec 31, 2015 #1

    MBBphys

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    Say I take a brick and push it and it moves, so work is done and chemical energy in my body is transferred into kinetic energy of the brick, which is then transformed to heat energy due to friction, so I have to keep pushing to transfer more of my chemical energy into kinetic energy of the brick. That I understand.

    But say I am pushing a wall hard with my palm, and neither the brick nor I move; does this mean I am not losing any chemical energy and no energy is being transferred out of my body?
    I.e. theoretically if I keep pushing the brick, I will lose the chemical energy store/lose mass, but then for the wall example, does the W=Fd formula mean I do not lose chemical energy/lose mass because the wall does not move?
    But surely energy is expended when I push the wall???

    I would much appreciate it if you could clarify this for me. Thanks in advance! :)
     
    Last edited by a moderator: Dec 31, 2015
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  3. Dec 31, 2015 #2

    haruspex

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    Even though the work done on the object relates to the distance the force advances, muscles do work just in exerting a force. Muscles contract by setting up an electrostatic potential between cells. I would guess there is some leakage, so work has to be done just to maintain the potential.
     
  4. Dec 31, 2015 #3
    No, work is not the only way to lose energy.
     
  5. Dec 31, 2015 #4

    CWatters

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    You expend energy because you are an inefficient biological machine. A spring wedged between two walls would happily push on them without expending any energy. The water in a swimming pool pushes on the walls without expending energy either.
     
  6. Jan 1, 2016 #5

    A.T.

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    Your body is converting chemical energy into heat all the time, even without you pushing anything.
     
  7. Jan 1, 2016 #6
    don't you get hot..and maybe frustrated pushing against this wall?..Heat is a form of energy...frustration is not !!
     
  8. Jan 9, 2016 #7

    MBBphys

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    Your example made it very obvious; thanks a lot!
     
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