Law of Conservation of Momentum

The conservation of momentum principle states that if two objects collide, the total momentum before and after the collision will be the same if no external force acts on the colliding objects. Or simply it can be stated as:

If there is no external force acting on the system, the momentum is constant. When two objects collide in an isolated system, the total momentum of the two objects before the collision equals the total momentum of the two objects after the collision.

When the net external force is zero, the momentum of the system remains constant, as expressed mathematically by the conservation of the linear momentum formula.

Final momentum (P_f) = Initial momentum (P_i)

From this it can be interpreted as, for any two or more bodies in an isolated system acting upon each other, their total momentum remains constant unless an external force is applied. Thus, it can be said that momentum can neither be created nor destroyed. This law is valid only for linear motion. Internal forces cannot change the total momentum of the system however they may change the momentum of each particle of the system.

For instance, in a rocket, fuel is burnt due to which gases are ejected downwards. Then the rocket moves up to conserve momentum. Fuel in a jet plane burns and ejects gases in a backward direction. Therefore, by conservation of momentum, the plane moves ahead.

Assume a fast truck collides with a stopped automobile, causing the automobile to begin moving. What exactly is going on behind the scenes? In this case, as the truck’s velocity drops, the automobile’s velocity increases, and therefore the momentum lost by the truck is acquired by the automobile. What do you think? Let’s learn more about the momentum and its discussion below: