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Ball bouncing on the floor - Normal reaction?

  1. Feb 22, 2008 #1
    Hey guys,
    Was just wondering if you could help me with what seems like a simple physics question.

    When a ball bounces on the floor, is the normal force greater than that of the weight, resulting in the bloor bouncing upwards?

    Or

    Is it the case where the normal reaction force is the same as the weight and the only reason why the ball bounces back up is because the balls kinetic energy is transformed into strain energy which inturn is converted back into kinetic energy?

    Or

    Neither of the two
     
  2. jcsd
  3. Feb 23, 2008 #2

    russ_watters

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    Staff: Mentor

    All of the first and sorta part of the second. The normal force is greater than the weight (it has to be fore a net acceleration) because of conservation of energy.
     
  4. Feb 24, 2008 #3
    "All of the first and sorta part of the second. The normal force is greater than the weight (it has to be fore a net acceleration) because of conservation of energy"

    Well ifs thats the case, why is the normal force greater. Doesn't Newtons third law state that for every action there is an equal but opposite reaction? So wouldn't this mean that the acceleration would be equal to the normal force?
     
  5. Feb 29, 2008 #4
    I think another reason is that action and reaction act on two different bodies. Ball exerts a force on the ground while ground in reaction,exerts a force on ball so it bounces up. They do not cancel each other's effect however they are equal in magnitude
     
  6. Feb 29, 2008 #5

    Doc Al

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    Staff: Mentor

    The normal force and the weight are not 3rd-law pairs. The pairs of forces that are equal and opposite per Newton's 3rd law are:
    1) The earth's force of gravity pulling the ball down (a.k.a., the weight) and the ball's force of gravity pulling the earth up.
    2) The contact force of the floor pushing up on the ball (the normal force on the ball) and the contact force of the ball pushing down on the floor.
    The acceleration of the ball is determined by the net force on it via Newton's 2nd law. During its interaction with the floor, the net force is upwards (Net force = Normal - weight), so the acceleration is upwards.
     
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