Newton's Law of impact

Newton described the elasticity of the collision by considering the velocities of approach and recession as shown in the following diagram.


Velocity of approach = u – u'
Velcoty of recession = v' – v

He defined a quantity known as the coefficient of resitituion (e) as:


This is known as Newton's Law of impact.

The ratio [v' – v]/[u' – u] must always be less than one except for a pefectly elastic collision where it is equal to 1. For a perfectly inelatic collision e = 0.

This means that in a perfectly elastic collision the velocity of approach of the two bodies before the impact is equal to their velocity of separation after the impact.

For an experiment to measure the coeffcient of restitution see: 16-19/Mechanics/Dynamics/Experiment guides/Coefficient of restitution