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# Introduction to Collision

We are familiar with many examples of collisions. We have seen two carrom coins or billiard balls colliding with each other or an automobile colliding with another. The molecules of a gas collide with one another. The collision of a neutron with an atom is well known.

In physics the term collision does not necessarily mean that a particle (or a body) actually strikes another. In fact, two particles may not even touch each other and yet they are said to collide if one particle influences the motion of the other.

For example, the positively charged alpha-particles speeding towards the positively charged nucleus of gold are simply deflected by the electro-static force of repulsion. In physics a collision between two particles (or bodies) is said to occur if they physically strike (or collide) against each other or if the path of the motion of one is influenced by the other.

When two bodies collide (e.g. when a bat strikes a ball), each exerts a force on the other. The two forces are exerted simultaneously and for an equal but short interval of time. According to Newton's third law of motion, each body exerts an equal and opposite force on the other at each instant of the duration of the collision.

During a collision, the two fundamental conservation laws, namely, the law of conservation of momentum and that of energy are obeyed and these laws can be used to determine the velocities of the bodies after the collision.