What are collisions? Explain the possible types of collisions.

Step 1: Collision

1. A collision happens when two bodies come in direct contact with each other. In this case, the two bodies exert forces on each other in a short period of time.
2. The energy and momentum of bodies interacting undergo a change as a result of the collision. Moreover, the collision may occur through actual physical contact of the bodies involved. For instance, the collision between two billiard balls.
3. There may not be any actual physical contact between the two bodies involved in the collision. For instance, the bombardment of alpha particles on the atomic nucleus.

Step 2: Types of collision

There are three types of collisions as follows:

1. Perfectly elastic collision
2. Inelastic collision
3. Perfectly inelastic collision

Parameter	Perfectly elastic collision	Inelastic collision	Perfectly inelastic collision
Definition	The kinetic energy before the collision is equal to the kinetic energy after the collision.	The kinetic energy before the collision is not equal to the kinetic energy after the collision.	In a perfectly inelastic collision, the two bodies stick together and move with the same velocity after the collision.
Coefficient of restitution	$\mathrm{e}=1$	$0<\mathrm{e}<1$	$\mathrm{e}=0$
Example	The collision between the atomic particles.	The collision between two vehicles on a road.	The firing of a bullet that is embedded in a wooden block.