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Conservation of angular momentum with energy

  1. Mar 5, 2010 #1
    Ice sketar rotates with open arms & her moment of inertia is I, rotational speed W. So, angular momentum is I*W. Energy is (1/2)I*W*W
    she folds her arms & her moment of inertia decreases to I/2. From conservation of angular momentum rotational speed became double say W*2.
    Energy became (1/2)*I/2*W*W*4 = I*W*W ( Energy is doubled, How?)

    Please tell me in this caculation where I am wrong?
  2. jcsd
  3. Mar 5, 2010 #2

    Doc Al

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    Staff: Mentor

    You're not wrong. The skater does work when she brings her arms in. She converts internal energy into rotational KE.
  4. Mar 5, 2010 #3
    Rotational kinetic energy isn't conserved
  5. Mar 6, 2010 #4
    OK, Very much Thanks for clearing my doubt.
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