Conservation of momentum:
The moving ball collides with a pin. The collision causes the ball to slow down and the pin to start moving.
Some of the momentum of the ball was transferred to the pin. The pin gains momentum and the bowling ball loses momentum.
Newton's third law, in combination with the second law, leads to one of the fundamental laws of physics.
This law is known as the principle or law of conservation of momentum. It is stated as: If no external force is acting on a system of two or more interacting bodies, the total momentum of the system is conserved.
In other words, for a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. In other words the momentum lost by object 1 is equal to the momentum gained by object 2. This law is valid even when masses of objects vary while in motion.
The collision (interaction between an object in motion with another so that there is a change in momentum (or impulse) is known as collision between two bodies) occurs in an isolated system as long as friction is small enough that its influence upon the momentum of the billiard balls can be neglected. If so, then the only unbalanced forces acting upon the two balls are the contact forces when the balls collide with each other. For such a collision, total system momentum is conserved.
There are four physical quantities – force, time, mass, and velocity change, that occur during collision. The force multiplied by the time is known as the impulse and the mass multiplied by the velocity change is known as the change in momentum. The impulse experienced by an object is always equal to the change in its momentum.