Newton's balls |
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A line of any number of elastic steel balls is suspended from a rail. A practical device has the balls on bifilar suspensions so they remain strictly in a line. When any number of balls are lifted from the end and released the oscillation proceeds in a regular way with the same number of balls taking part. That the same number of balls leave the opposite end of the line with the same velocity is a demonstration of the simultaneous conservation of momentum and kinetic energy. The cradle works properly only if the collisions are perfectly elastic |
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A two ball clacker is a form of Newton's balls. |