Collisions With Walls
When a ball strikes a wall at right angles with a speed
it will rebound with a speed
where
is the coefficient of restitution between the ball and the wall.
In general however the ball will not strike the wall at right angles, but at some glancing angle, as shown below.
In this case the speed of the ball after the collision is not
We can use the principle of restitution, which states
resolving
perpendicular and parallel to the wall. The approach and separation speeds are the components ofperpendicular to the wall before and after the collision, as shown below.
The approach speed before the collision is
and the separation speed after the collision is
The principle of restitution gives
The components of the velocities parallel to the wall are unchanged, since the impulse received by the ball is perpendicular to the wall, so that
The kinetic energy of the ball after the collision is not then
as for the head on collisions, but
