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If i use a certain amount of energy/work - lets say 0,36 J - to wind

  1. Feb 29, 2012 #1
    If i use a certain amount of energy/work - lets say 0,36 J - to wind up an old alarm clock, will the mass of the clock increase, or will the clock just get hotter somehow?
     
  2. jcsd
  3. Feb 29, 2012 #2
    Re: E=mc2

    Good question. In general, it depends on the particulars of the situation. In the case of an alarm clock, there is generally a system of springs which stores the energy and potential energy---which would increase the effective mass of the system. At the same time, energy is always lost to heat (especially the bearing, and the spring's metal).
     
  4. Feb 29, 2012 #3
    Re: E=mc2

    I would think that the mass in the spring would get hotter and denser, but not bigger? Would it really weigh more than before?
     
  5. Feb 29, 2012 #4
    Re: E=mc2

    It doesn't get any 'bigger' in size; but yes, the mass of the system would increase. This is a measurable effect in atomic nuclei where the total mass is larger for a bound system than for the constituent parts alone (same idea of potential energy being stored in the system).
     
  6. Feb 29, 2012 #5

    Drakkith

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    Staff: Mentor

    Re: E=mc2

    Mass is a property of matter, it cannot get hotter and denser itself. If you increase the mass of something it will weigh more than it did before.
     
  7. Feb 29, 2012 #6
    Re: E=mc2

    Can somebody explain this please- I'm now a little confused.
     
  8. Feb 29, 2012 #7

    Drakkith

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    Staff: Mentor

    Re: E=mc2

    What are you confused about?
     
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