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Acceleration of a bouncing ball (no calculations needed)

  1. Sep 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A hard rubber ball is bounced on the floor. Compare the ball's acceleration on the way down to its acceleration on its way back up.


    2. Relevant equations
    -


    3. The attempt at a solution[/b
    First off, ignore air resistance.
    Lets assume that the person bouncing the ball uses some force and doesn't just drop the ball. This would mean that the acceleration of the ball would be
    Initial force used + 9.8m/s^2, correct?

    The bounce would absorb some of the initial force, but no all of it, correct?

    The gravitational pull would be symmetrical so the end result would be

    (Initial force - absorbed from bounce) + 9.8m/s^2, correct?
     
  2. jcsd
  3. Sep 1, 2012 #2

    Doc Al

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    Staff: Mentor

    It's much simpler than you think.

    What forces act on the ball after it leaves the person's hand and is on the way down?
    What forces act on the ball after it bounces off the floor and is on the way up?
     
  4. Sep 2, 2012 #3
    All I can think of is gravity which would be symmetrical if you throw the ball up and wait for it to come down. Where I get confused is the bounce part. Doesn't the bounce make the ball lose some of it's energy?
     
  5. Sep 2, 2012 #4

    Doc Al

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    Staff: Mentor

    Sure, but so what? They are asking about the acceleration of the ball while it is in the air, not about the energy it has.
     
  6. Sep 2, 2012 #5
    also they are just asking about while it's going down and while it's going up, not about when it hits the ground
     
  7. Sep 2, 2012 #6

    Doc Al

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    Staff: Mentor

    That is exactly right. While its going up and going down, the only force acting is gravity. So what must be the acceleration?
     
  8. Sep 3, 2012 #7
    a= 9.8 m/s^2

    The force used by the thrower doesn't count because it only acted at the instant when the ball was thrown?
     
  9. Sep 3, 2012 #8

    Doc Al

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    Staff: Mentor

    Correct. (What direction is the acceleration?)
    Exactly. As soon as the ball leaves the thrower's hand, the only force acting is gravity.

    Same for the floor when it bounces: As soon as the ball leaves contact with the floor, the floor no longer exerts a force on the ball.
     
  10. Sep 3, 2012 #9
    Ah I see! The direction must be down. Thank you so much for clarifying :)!
     
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