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Thermodynamics- Conservation of energy

  1. Mar 9, 2015 #1
    1. The problem statement, all variables and given/known data
    Hello everyone, I was hoping I could get someone to help me out please. I am having great difficulty with my thermodynamics course and I have an assignment due tomorrow.
    I need to reduce the conservation of energy formula so that it applies to earth so I can work on my assignment.

    2. Relevant equations
    (Qin-Qout) + (Win- Wout) + (Emass,in- Emass,out)= ΔU + ΔKE + ΔPE

    3. The attempt at a solution
    This is the way I think it is
    (Qin-Qout) + (Win- Wout) = ΔKE + ΔPE

    please let me know if I'm right or if I should add or remove other components
    Thank you
     
  2. jcsd
  3. Mar 9, 2015 #2

    Simon Bridge

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    We need the context and the specific meanings of the letters to hep you.
    Note: for conservation of energy, the total change in energy is zero. If you have anything left over, energy is not conserved.
    In thermodynamics, the "system" is usually not closed in this way - energy enters of leaves the (say) gas as heat, work, or with the mass (i.e. as kinetic energy in an escaping gas). So the LHS of your relation looks good. The RHS is a bit of a mystery, it looks to me like you have terms from different models.
    These would be internal energy contributions from different sources right?

    So it would help to see your reasoning.
     
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