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Homework Help: Lagrangians and P-Conservation

  1. Oct 19, 2006 #1
    I have a problem with a particle experiencing a central force towards some origin, as well as a gravitational force downwards. I've calculated the Lagrangian, and the equations of motion. Now I'm being asked to see if the system follows conservation of angular momentum. How do I do this? I know it has something to do with seeing if the system is invariant of rotation, but how do I check for that?
  2. jcsd
  3. Oct 19, 2006 #2
    If [tex]\frac{\partial L}{\partial q} =0[/tex] then the conjugate momentum [tex]\frac{\partial L}{\partial \dot{q}}[/tex] is a conserved quantity.

    If that doesn't clear things up, then post what you have for the Lagrangian.
  4. Oct 20, 2006 #3
    But the conjugate momentum is the same as the angular momentum only in some cases.
    Compute H and chech if H commutes with J.
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