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Energy a scalar

  1. Oct 29, 2013 #1
    I am having trouble understanding why energy is a scalar. (1/2 mv^2, mgh, 1/2kx^2, etc).
    Can someone just briefly hit over why? I tried asking a few people but I still don't get it. Thanks.
  2. jcsd
  3. Oct 29, 2013 #2


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    Because that's what is conserved.
  4. Oct 29, 2013 #3


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    For every (continuous) symmetry a physical system inhibits, we have a conserved quantity. The translation invariance in 3 spatial directions leads to 3 momentum components which are conserved. The temporal translation invariance leads to energy conservation.

    In relativity, the 3-vector of momentum is combined with energy to form the 4-momentum.
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