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Pulling a Tablecloth from Under a Steel Ball

  1. Nov 8, 2004 #1
    Ok so I'm guessing my TA made up this problem on his own so I don't know how to start, considering there are no numbers and lol I just love having numbers to work with. Anyways here goes.

    A tablecloth covers a horizontal table and a steel ball lies on top of it. The tablecloth is pulled from under the ball (in a perfectly horizontal fashion), and friction causes the ball to move and roll. What is the ball's speed on the table when it reaches a state of rolling without slipping? Assume that the table is large enough that the ball does not fall off of it.

    Help! :eek:
  2. jcsd
  3. Nov 8, 2004 #2
    As the table cloth is pulled from under it, friction makes the ball start to roll. Assuming this takes place long enough, the ball will start spinning with the same speed as the table cloth is pulled. Once the cloth is gone, it will touch the table and slow down a little because its now slipping. Once its slow enough for friction to get it moving, it should move with a little less than the speed at which the table cloth was pulled. Im guessing though.
  4. Nov 8, 2004 #3
    thanks for your thoughts, hope someone else has an idea
  5. Nov 8, 2004 #4
    You must be primarily concerned of the system where 1) friction allows the ball to accelerate without slipping, or where the slipping involves either 2) a typical critical frictional "breakaway" from static to kinetic friction or 3) the sphere experiences a quantity of torque from the tablecloth divided by the moment of inertia that exceeds the acceleration at point of contact.
  6. Nov 8, 2004 #5
    well as of now I'm assuming that the speed the cloth is pulled is equal to the speed of the rolling ball, but from there I'm lost.
  7. Nov 9, 2004 #6
    If the ball is rolling without slipping then wouldn't the angular momentum just be equal to Vcm/R?
  8. Nov 10, 2004 #7
    This is an interesting question. Can somebody please set a question related to this one. Anything will do. I just want to see how this question could be asked. My final exam is impending. I'm thinking that my lecturer might design all the weird questions for us. Thanks
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