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Impact of a ball due to gravity and momentum

  1. Sep 21, 2007 #1
    Just a quick question of of curiosity. It's basic physics but I can't remember it :redface:

    Lets say you have two balls of equal mass about 3 meters up on a ledge. You let one drop straight down, it hits the ground and stops. The other one is pushed forwards with a speed of lets say 1m/s and then hits the ground further out and continues to roll.

    Which ball takes more impact? If I remember correctly, each ball has separate x and y components so they both would land with the same impact, but I am not sure. Can anyone please elaborate?

    Thank you!
  2. jcsd
  3. Sep 21, 2007 #2


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    Staff: Mentor

    Both have the same vertical velocity, but the one with a horizontal velocity has a little more kinetic energy. Velocity is a vector and horizontal and vertical components add.

    The impulse from vertical impact would be the same, but horizontal compenent would provide a shear component to the impact.

    If the collisions were purely elastic, but with friction, the ball with the horizontal component would spin, but both balls would bounce back to the same height.

    Without friction, the ball with the horizontal velocity would not have spin but would continue to travel horizontally at the same speed (assuming we neglect air resistance).
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