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B Work and energy

  1. Mar 12, 2017 #1
    Why do we exhausted sometimes even when no work(in terms of science) is done.where does our energy go?
  2. jcsd
  3. Mar 12, 2017 #2


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    Staff: Mentor

    Ah, but you are doing work! If you push on a brick wall, even though you do no work on the wall itself, your muscles are doing work on themselves because they aren't rigid objects and will stretch slightly as they try to contract. All of the work is eventually turned into heat through this and through the chemical processes fueling your muscles.
  4. Mar 13, 2017 #3


    Staff: Mentor

    Even when you are sitting, your body breathes, circulates blood, thinks, and creates new flesh and bones.

    It is very difficult to use physics to trace where the energy goes in living beings, or to use physics to explain what feeling tired means.

    Physics is a tool. A good tool. But it is not the best tool for every job.
  5. Mar 13, 2017 #4


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    Science Advisor
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    Gold Member

    The human body is a biological machine. Parts can "fail" or temporarily wear out despite there being lots of "fuel" in the tank.
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