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Inelastic collision of two soccer balls of different masses

  1. Oct 8, 2006 #1
    You might or might not have seen the astro blaster. But if you drop two soccer balls (stacked together) you'll notice that the smaller top soccer ball lifts up to great heights. Im researching this phenomenon for my extended essay and would really appreciate it if you guys could provide me with some good papers on inelastic collisions. So far I've only been able to incorporate the elastic collison equation along with COR.


    Help and ideas would be really appreciated.
    Specially Information about loss from spin etc.

  2. jcsd
  3. Oct 8, 2006 #2

    Andrew Mason

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    I would not concentrate much on the inelastic nature of the collision. The collision is inelastic only for the time that the balls are deformed. At this time, the kinetic energy of the balls is stored as potential energy in the compression of air inside the ball. You have to examine that potential energy and its conversion back into kinetic energy, then analyse the relative timing of the compression/expansion of the two balls in order to explain what happens.

  4. Oct 8, 2006 #3
    The elastic collison equation actually gives me the 9x theoretical velocity amplification I hypothesized, however I've already conducted my experiment ( I increased the mass of my top ball by adding weight making it eventually 5 times heavier than the orignally larger ball). I noticed a decrease in the lift off height, now i need to write about the energy losses incurred and the effect of mass on the rebound height.

    Do I make any sense? OR am i just rambling/
    Thanks AM for trying
  5. Oct 8, 2006 #4
    I guess I have to be a lot more specific to get help. I have two soccer balls and lets say bouncing each of them independently i get two seperate coefficient of restitutions for the two balls.
    Now in this equation which c is being talked about?
    Is it the c of only one of the balls with the floor or is it c1*c2.
    Does this equation cover both the energy loss in the collision between the balls and the floor/ or only the balls with each other?
  6. Oct 8, 2006 #5


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    The floor's elasticity counts also, so it's c1*c2*c3 (c3 being the floor). Also, the ideal situation, where only the top ball bounces and the bottom ball remains in contact with the floor doesn't always happen. If the bottom ball leaves the floor, then it's using up some of the total kinetic energy after the bounce.

    A similar thing can be done on a trampoline. Multiple people land on a trampoline at the same time, then all but one of them quickly raise their legs to pull them off the trampoline, so all the downwards energy from the mulitiple people now goes into catapulting the solo victim skyward.
    Last edited: Oct 8, 2006
  7. Oct 9, 2006 #6
    The floor has a value of restitution? sounds very absurd !
    Doesnt measuring the rebound height and orignal height of a bouncing ball measure the coefficient of restitution of the ball and floor.
  8. Oct 9, 2006 #7


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    Yes, it's really the interaction between ball and floor. Dropping a soccer ball on mud will produce less bounce than dropping it on a solid marble floor.
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