How exactly does a newton’s cradle work?

I understand that it has to do with conservation of momentum. But why is it that if you pull one ball back and drop it only the one on the end is affected. Why don’t all 4 of the balls move with 1/4 as much momentum?
Update: I meant to say velocity instead of momentum for the last word.
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General Physics RvTDLR 4 years 1 Answer 471 views 0

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Answer ( 1 )

  1. Yes but it also has to do with conservation of *energy*.
    Steel balls exhibit pretty elastic collisions (heh), so the mechanic (kinetic) energy is almost completely conserved on each strike.

    When the 1st ball drops with say speed “v” then it has momentum mv and energy 0.5mv^2.
    If each of the 4 balls rebounded with speed v/4, then the momentum would be conserved.
    But total energy = 4 * 0.5m(v/4)^2 = 0.125mv^2, which is a 75% loss – maybe with play dough balls when they get squished etc.

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