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In a hypothetical world where there is no friction, and all collisions are elastic would an object in lateral motion be perpetually moving and never come to a stop?

Assumptions:

  • Perfect vacuum: zero air friction
  • Elastic collisions: no loss of momentum
  • Zero friction with the ground
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  • $\begingroup$ Conservation laws tell yes. If there is no momentum lost, it will be there forever. $\endgroup$
    – Jan2103
    Commented Sep 10, 2019 at 21:35
  • $\begingroup$ Elastic means no loss of kinetic energy. $\endgroup$
    – my2cts
    Commented Sep 10, 2019 at 22:19
  • $\begingroup$ No: gravitational radiation will take energy out of the system. $\endgroup$
    – JEB
    Commented Sep 11, 2019 at 2:22
  • $\begingroup$ How would you define moving? Relative to what. A single moving ball in a void would be indistinguishable from a stationary one. $\endgroup$
    – John Meacham
    Commented Sep 11, 2019 at 21:12

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Not necessarily. For example, if a moving ball were to hit another ball of the same mass at rest, the moving ball could stop dead, having transferred all it's momentum to the other ball.

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  • $\begingroup$ but this assumes another ball was already at rest. $\endgroup$
    – Natsfan
    Commented Sep 10, 2019 at 22:40

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