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Angular momentum of a system

  1. Oct 16, 2011 #1
    I do not understand this one step in deriving the angular momentum theorem for a system of particles.

    The vector angular momentum about the point Q, not necessarily the origin is..
    [PLAIN]http://img27.imageshack.us/img27/8196/pfquestion.gif [Broken]

    I do not understand why the difference in the velocities of the point Q and k equals the DERIVATIVE of the momentum. If you bring the mass term into the expression, then shouldn't it be equal to just p? Why is it dp/dt??
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 16, 2011 #2
    Never mind, I just got it by differentiating. Now what I don't get is the next part. I will post a pic soon.

    Okay so, when I differentiate the expression for angular momentum, I get the expression above. When THEY differentiate it, they get what I have plus this additional term.

    [PLAIN]http://img24.imageshack.us/img24/9514/pfquestion1.gif [Broken]

    Maybe I am being oblivious again, but I cannot get this term to make sense!
    Last edited by a moderator: May 5, 2017
  4. Oct 16, 2011 #3
    Yup! being oblivious again! I got it. I think on that note, I should finally stop studying haha.
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