<P> The coefficient of restitution (COR) is the ratio of the final to initial relative velocity between two objects after they collide . It normally ranges from 0 to 1 where 1 would be a perfectly elastic collision . A perfectly inelastic collision has a coefficient of 0, but a 0 value does not have to be perfectly inelastic . It is measured in the Leeb rebound hardness test, expressed as 1000 times the COR, but it is only a valid COR for the test, not as a universal COR for the material being tested . </P> <P> The value is almost always less than one due to initial translational kinetic energy being lost to rotational kinetic energy, plastic deformation, and heat . It can be more than 1 if there is an energy gain during the collision from a chemical reaction, a reduction in rotational energy, or another internal energy decrease that contributes to the post-collision velocity . </P>

For perfectly elastic body the value of coefficient of restitution is