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Why doesn't a spinning coin flip over?

  1. Aug 30, 2013 #1
    As titled:

    I would be satisfied with a qualitative explanation(pure physical), but it would be nice if someone can also provide the mathematical model.

  2. jcsd
  3. Aug 30, 2013 #2


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    Staff: Mentor

    Are you asking why it doesn't stop spinning and flop over onto one of its sides? Just not sure what you mean by "flip over".
  4. Aug 30, 2013 #3


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    Gold Member

    Remember conservation of angular momentum.

  5. Aug 31, 2013 #4

    oh sorry I should be more clear.

    I meant why doesn't it fall down on the ground(flat) as a stationary coin would.
  6. Aug 31, 2013 #5


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    Staff: Mentor

  7. Aug 31, 2013 #6


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    It follows from Euler's equations. If there is an Omega_z (z is the axis of the coin), and I_z is larger than I_x and I_y, Omega_x and Omega_y follow SHO, and oscillate without flipping over.
    You can win money with that, just don't get caught.
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