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Bouncing a ball

  1. Aug 7, 2006 #1


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    When a ball bounces into something like the floor the component of the speed normal to the plane (for example the floor) gets reversed.
    I'm trying to program a physics simulation were there are, among other things, balls bouncing off walls and stuff. Now I know that I could simply reverse the speed component as I explained above to make the ball bounce but this is somewhat af a "hack", what I want to know is how it "really" happens - in terms of forces and stuff. The ball changes it's momentum which means that there is some force that pushes the ball from the wall over a certain time - impulse. How do I calculate this force (by perimiters such as the rigedness of the wall, speed of the ball...) and how do you know when to apply it and when to stop?
  2. jcsd
  3. Aug 7, 2006 #2
    If it were me, I would start with the mass and spring model. Let the velocity decrease linearly to zero then increase back to where it was, but in the other direction. Keep the slope the same no matter how fast the ball approaches the wall. This will create the parabolic motion that a bouncing ball in contact with the floor in slow motion would so closely resemble.

    Relevant Newton's Equations:

    (velocity) = (initial velocity) + (acceleration) x (time)

    (Position) = (initial position) + (initial velocity) x (time) +
    1/2 (acceleration) x (time)^2

    The acceleration is of course in reality determined from the force and the mass, and the force is determined from Hooke's Law F = -kx where k is the spring constant which you can play with, but you could also just play with the acceleration until it looks right.

    Are you going to consider energy loss? i.e. will the ball eventually stop bouncing?
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