Collision is an event that demands involvement and interaction of at least two objects. In course of occurrence of such event interaction amongst object occur and each object experiences impulsive forces – a force which occur for a very small duration, from other.

This impulsive force is responsible for change in momentum of the object in collision. Collision can occur amongst subatomic particles collision between comer and the sun. They get deflected before actually reaching the other due to encountering huge force, impulsive force – force proportional to Inverse Square of distance.

What is head-on Collision and Oblique Collision?

Head on Collision: It happens when velocities of both the particles are along the line of collision. This can be regarded as a collision in one dimension. Car accident is one of the basic examples of one-dimension collision.

Head on Collision

Oblique Collision: It happens when any of the two bodies have velocity at an angle with the line of collision. In case of an oblique collision, the component of velocity perpendicular to the line of the collision remains unchanged. This can be regarded as collision in two dimensions.

Oblique Collision

Classification of Collision: Collisions can be classified on the basis of whether kinetic energy remains constant or not. If the kinetic energy of the system remains constant then it is known as an elastic collision. While there are situations when some of the kinetic energy gets converted into heat, deformation of shape etc. These types of collisions are known as inelastic collision.

We define another quantity known as coefficient of restitution (e).

Coefficient of Restitution (e): It is defined as the ratio of velocity of separation by velocity of approach along the line of collision.

Coefficient Restitution (e) = \(\frac{{{V}_{2}}\,-\,{{V}_{1}}}{{{U}_{1}}\,-\,{{U}_{2}}}\),

Coefficient of Restitution

Depending on the values of e we can infer the type of collision.


e = 1, it is elastic collision,

0 < e < 1, it is inelastic collision,

e = 0, it is perfectly inelastic collision.