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Action definition

  1. Jan 24, 2009 #1

    why is the action defined as the integral of the Lagrangian over time?
    i don't see the meaning of integral on the (kinetic - potential) energy

  2. jcsd
  3. Jan 24, 2009 #2


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    The integral has no meaning by itself, but setting its variation equal to zero leads to the equations of motion.
  4. Jan 24, 2009 #3
    You can see the integral as a way of measuring how much of something is used. So in this case, the integral measures how much (K-U) energy is being used up, and the path that a particle takes minimizes this (this isn't technically correct... it takes a 'stationary' path, but looking at it this way could be beneficial to the student visually).
  5. Jan 25, 2009 #4
    thanks for the replay.

    I found a detailed explanation in the Feynman lectures on physics vol 2
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