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Homework Help: Trying to understand moment of inertia; example of a rod

  1. Feb 23, 2006 #1
    i found smtg that i don't understand.moment of inertia = 1/3 m(r^2) stands for which type pf rod??or reference point??
  2. jcsd
  3. Feb 23, 2006 #2

    Doc Al

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    Staff: Mentor

    The moment of inertia of a thin rod of length L about one end is:
    [tex]I_{end} = \frac{1}{3} M L^2[/tex]

    About the middle, it would be:
    [tex]I_{cm} = \frac{1}{12} M L^2[/tex]

    (Set up the integral [itex]\int r^2 dm[/itex] and see for yourself!)
  4. Feb 23, 2006 #3
    Don't understand something like that. Do the integration by yourself and derive the result. Anyway it is for the moment of inertia of a uniform rod, suppose AB, with respect to its ends A or B.
    There is no complication in the integral. Just think about relating dm with dr.
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