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Homework Help: Question about Centripetal Force (How it could make object glued to the wall.)

  1. Feb 1, 2012 #1
    1. The problem statement, all variables and given/known data

    A man standing inside a cylinder rotating with a particular angular velocity ω could take his feet off the ground and stay 'glued' to the wall of the cylinder. Draw the free body diagram of the man.

    3. The attempt at a solution


    My question is how the gravitational force is to be canceled by a force that acts perpendicular with it? Could it be that the normal force of the object rotating in circular path is causing the friction to increase significantly that it could actually counter act the gravitational force?

    What happen if the wall is frictionless, would the man stay glued?

    If the friction is the one that causes our body to stick how this could explain the whirling of a ball in the air perpendicular to the surface of the Earth in circular motion that it does not fall to the ground whilst it is still moving?

    Is Newton laws still valid for the man considering that the man is in constant acceleration?

    Thank You
  2. jcsd
  3. Feb 1, 2012 #2


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    the whirling causes the ball to rise up is caused by the tension of the string which has to be at an angle of same ratio to the centripetal force and gravity.

    The rest of your reasoning looks good to me
  4. Feb 1, 2012 #3
    Then it is safe to say that if the wall of the cylinder is frictionless, the man would fall?
  5. Feb 1, 2012 #4


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    i believe he will
  6. Feb 1, 2012 #5
    Could you elaborate further on this point, perhaps in terms of equations?
  7. Feb 1, 2012 #6
    Yes. In your free body digram you need to add the frictional force, directly upwards.

    No, he would slide down.

    If a ball is whirled in a horizontal circle, the string might look horizontal, but in fact it is at an angle with the horizontal: the ball will be lower than the point about which the string is rotating. If you draw a free body diagram of the ball there will be two force vectors, the ball's weight acting directly downwards and the force from the string acting diagonally upwards. The vertical component of the force coming from the string will balance the downward force of the weight of the ball, while the horizontal component of that force provides the acceleration. For the string to be near horizontal, the tension in the string must be many times the weight of the ball.

    Yes, if we take this acceleration into account.
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