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Physics behind Newton's Cradle

  1. May 19, 2012 #1
    So, since the newtons cradle is all about the conservation of momentum. I was wondering, when one ball is released from one side at a certain velocity, why doesn't two balls at the end swing, at half the original speed?
  2. jcsd
  3. May 20, 2012 #2


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    It's not just conservation of momentum. Most of the energy is conserved too. Two balls at half the speed would only be half the energy.
  4. May 20, 2012 #3
    The usual steel balls used in the Newtons Cradle are efficiently elastic, meaning they don't lose a lot of energy as heat. This implies most of the energy is conserved. If some other non-elastic material was used, this wouldn't be the case.
  5. May 20, 2012 #4
    why would two balls be only half the energy?
  6. May 20, 2012 #5
    Say the initial single ball of mass m has velocity V, and the two balls each(of mass m) have velocity V/2. Can you find out their kinetic energies and co-relate them?
  7. May 20, 2012 #6
    Then why couldn't the other 4 balls move with velocity V/2? In this case both sides have equal kinetic energy, thereby conserving the energy in the system.
  8. May 20, 2012 #7
    The momentum isn't conserved in this case :wink:
  9. May 20, 2012 #8


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  10. May 20, 2012 #9


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