Conservation of Momentum

If two bodies interact, the vector sum of their momenta remains unchanged, provided the force of mutual interaction is the only force acting on them. The same has been found to be true for more than two bodies interacting with each other. Generally, a number of bodies interacting with each other are said to be forming a system. If the bodies in a system do not interact with bodies outside the system, the system is said to be a closed system or an isolated system.

In an isolated system, the vector sum of the momenta of bodies remains constant. This is called the law of conservation of momentum.

According to Newton’s second law of motion, the change in momentum ∆p of a body, when a force F acts on it for time ∆t, is

∆p = F ∆t

This result implies that if no force acts on the body, the change in momentum of the body will be zero. That is, the momentum of the body will remain unchanged.