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Energy Question

  1. Aug 1, 2007 #1
    I have a question regarding the conservation of energy. If I were to push a medium sized box across a surface, I would be imparting a certain amount of energy to it (and myself) and also dissipating a certain amount of thermal energy into the surface. This energy I'm supplying comes from the transfer of the chemically stored energy in my body when I push the box, yes?

    Now, if I were to expend an equal amount of bodily energy pushing against a large box, and was not able to overcome the friction force, would all that energy be instead dissipated as thermal energy into the ground and box? Maybe I'm just overestimating the awesomeness of kinetic energy, but intuition (often wrong, admittedly) tells me that the thermal energy produced in the second scenario would not be equivalent to the kinetic and thermal energy my efforts produced in the first. Apologies for a potentially dumb question, but could someone explain this?
  2. jcsd
  3. Aug 1, 2007 #2
    Yes indeed, you transfer energy to ground (in both cases).
    In fact u cannot push a box against a wall if the wall is not well connected to the ground.

  4. Aug 1, 2007 #3
    No. In the second case, since you did not overcome friction, no work was done on the box and whatever (food/chemical) energy was merely dissipated as thermal energy within your body.
  5. Aug 1, 2007 #4
    But if that's the case, I would get hotter pushing something that didn't move than pushing something that did, even if I was expending the same amount of energy. That doesn't make sense to me.
  6. Aug 1, 2007 #5


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    Staff: Mentor

    Why not? Try it! You will most certainly get hotter if you push hard on an immovable wall for more than a few seconds.
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