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What is and how do I use the Parallel axis theorem

  1. Nov 13, 2011 #1
    I have in my problem, a ball sitting on a cylindrical rod that pivots at the bottom,
    some guy in the explanation said parallel axis theorem and came up with moment of inertia of:
    I = (mL^2)/3 + [2Mr^2/5 + M(L+r)^2]

    where L is the length of the rod, m is the mass of the rod, M is the mass of the ball, r is the radius of the ball.
  2. jcsd
  3. Nov 14, 2011 #2
    I assume you've covered moments of inertia, the parallel axis theorem then states that if you're rotating your object about an axis parallel to a second axis where you know the rotation moment of inertia then the new moment of inertia about your displaced axis is equal to the "normal" moment plus a term [itex] md^2 [/itex] where m is the mass of the object and d is the distance between the axes (?) .
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