“Mutual interaction between two bodies for short time due to which their momentum and energy are changed, is called collision.”
For examples: Collision of cricket ball with bat; collision of two billiard balls; collision of gas molecules etc. In all these collisions, there is physical contact. When an α-particle moves towards a nucleus, then due Coulomb force (repulsion), the α-particle is scattered without physical contact. This is also, the example of collision.
Kinds of collision:
(i) Perfectly elastic collisons: The collision in which the energy and momentum of the system remain conserved separately, is called perfectly elastic collision. For example: collision of gas molecules.
Properties of perfectly elastic collisions:
1. Total momentum of the system remains conserved.
2. Total energy of the system remains conserved.
3. The forces applied by the bodies on each other are conservative.
(ii) Non-elastic collisions: The collision in which the momentum remains conserved but mechanical energy does not remain conserved, is called non-elastic collision. For example; collision of two vehicles in road accident.
Properties of non-elastic collisions:
1. Total momentum of the system remains conserved.
2. Total energy of the system remains conserved.
3. Mechanical energy of the system does not remain conserved.
4. Some part of mechanical energy is converted in sound, heat and light energy.
5. Internal attractive forces of the system are non-conservative.
(iii) Perfectly non-elastic collisions: The collision in which the momentum of the system remains conserved but mechanical energy does not remain conserved and after collision both bodies move with same velocity in same direction i.e, both bodies get attached with each other. For example, when a bullet is fired on wooden block then it penetrates and remains in it.
Properties of perfectly non-elastic collisions: The properties of these collisions are same as those of non-elastic collision. Only the difference is that after collision the bodies are attached with each other.
(iv) Super elastic Collision: In such type of collision, there is an increase in kinetic energy. This occurs if there is a release of potential energy on an impact.
Examples: Bomb blasting
The coefficient of restitution is always greater than 1 in super elastic collision.
