I read in a book that in both elastic and inelastic collision, the interacting forces after the collision become effecitively zero, the potential energy of the system remains the same both before and after the collision. I didn't get that. Is that so because the internal forces are conservative? But they can be non conservative too.

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    $\begingroup$ Can you give a reference or even a direct quote? $\endgroup$ – Aaron Stevens Jul 8 at 15:32
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    $\begingroup$ The claim seems evidently false. If the potential energy were to remain the same before and after the collision, the kinetic energy would also remain the same due to energy conservation. If that is the case, it is the definition of elastic collisions. So, such a description manifestly excludes inelastic collisions. $\endgroup$ – Dvij Mankad Jul 8 at 15:34
  • $\begingroup$ Are they talking of classical particles colliding or quantum mechanical? If it is a collision only dp/dt takes place classically and before and after the time of collision there is no force. $\endgroup$ – anna v Jul 8 at 16:18
  • $\begingroup$ Classical particles colliding $\endgroup$ – user235357 Jul 8 at 16:23
  • $\begingroup$ books should be written to clarify, not obfuscate. $\endgroup$ – JEB Jul 8 at 16:29