Elastic Collision: Isolated Systems & Conservative Forces

[sauri]

In an elastic collision both momentum and kinetic energy are conserved which means only conservative forces are acting (therefore no friction!).
So that must mean we also have to be in an isolated system, so no energy is lost due to external forces. Can this state actually exist in reality?. Any examples?.

 

[Meir Achuz]

If the collision takes place in a short enough time, outside forces can be neglected. The impulse due to an outside force is Fdt-->0 as dt-->0.
The force between the two colliders is impulsive in that Fdt is finite.

 

[sauri]

any examples where we might see elastic collision happening? I can not imagine any collision happening in such a small period of time

 

[Eivind]

Two electrons colliding.