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What will happen to the rotational motion

  1. May 3, 2005 #1
    if a body is rotating forward towards a wall,colides with the wall ofcourse the direction of motion will be reversed,,but what will happen to the rotational motion,if it is given that the infinitely rough
  2. jcsd
  3. May 3, 2005 #2


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    Did you stop in the middle of a sentence? Acutally "of course the direction of motion will be reversed" is not "of course" at all. If there is no friction (and the collision is perfectly elastic) then the body would go back in exactly the opposite direction with exactly the same spin. If there is friction however (I don't think it needs to be "infinitely rough"!) The ball exerts some force on the wall in one direction and so will not go straight back but slightly of to one side while its rotation slows slightly. What "slightly" is depends upon the friction.
  4. May 3, 2005 #3
    The translational motion (not rotation) will be reverse if the wall is perfectly elastic and will not fail upon impact. The rotation will change depending on the friction of the wall. The range of rotational change will be from a rotation that is slightly slowing down to a rotation of opposite spin with the same magnitude. The same magnitude requires ideal conditions which you can figure out because I will probably leave some assumptions out. Can someone list all the ideal conditions for the translational and rotational motion to be reversed upon impact of the wall?
  5. May 3, 2005 #4
    Translational motion is conserved in a perfectly elastic frictionless collision.
    Rotational is another thing though. For the rotational to be stopped, the wall would need to impart an angular impulse such that its magnitude is exactly that of the spinning ball (and opposite direction). If this is done in an infinitely small time period (to maintain the elastic requirement) the ball will lose all its rotational motion. An example is if you threw it at something like a conveyor belt. To reverse the motion with the same magnitude, your angular impulse would need to be twice as strong as the initial angular momentum of the ball.

    Ofcourse these are idealistic, and not physically possible to replicate.
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