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Homework Help: Spinning situation

  1. Nov 28, 2008 #1
    1. The problem statement, all variables and given/known data

    Suppose you are standing on the center of a merry-go-round that is at rest. You are holding a spinning bicycle wheel over your head so that its rotation axis is pointing upward. The wheel is rotating counterclockwise when observed from above.

    For this problem, neglect any air resistance or friction between the merry-go-round and its foundation.

    Suppose you now grab the edge of the wheel with your hand, stopping it from spinning.
    What happens to the merry-go-round?

    A. It remains at rest.
    B. It begins to rotate counterclockwise (as observed from above).
    C. It begins to rotate clockwise (as observed from above).

    2. Relevant equations


    3. The attempt at a solution

    the merry go round cannot stay at rest because the angular momentum from the spinning bicycle wheel cannot disappear.

    the merry go round will spin counterclockwise (as observed from above) because that the direction the wheel was spinning?

    Attached Files:

  2. jcsd
  3. Nov 29, 2008 #2

    I hope you are familiar with the condition that is required for the conservation of angular momentum. In addition, recall that there is a simple equation describing the relationship between angular velocity and angular momentum. (Remember, angular velocity is a vector, and the sign conventions will determine the direction of revolution.)

  4. Nov 29, 2008 #3
    We will assume this system is a rigid body rotating around a symmetry axies.

    In this case L = I \omega (all vectors) .

    L is conversed as the external torque on the system is 0.

    Hence to keep the same angular momentum vector as the wheel comes to a stop, you and the merry go-ahead must start spinning in the same direction ie counter clock wise.
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