In a recent paper, Bashkansky and Netzer1 considered a one-dimensional elastic collision between a target particle of mass m and an incident particle of mass M. They observed that the energy efficiency η, given by the energy transferred to the target particle divided by the initial energy of the incident particle, is given by

η=4α(1+α)2=4α1(1+α1)2,
(1)

and is a function only of the mass ratio α=Mm. If the two particles have the same mass, α=1 and hence η=1, and there is total energy transfer, as illustrated by every Newton’s pendulum ornament. In contrast, as the mass difference increases, α or α0, and the efficiency...

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