Law of conservation of momentum
“For two or more bodies in an isolated system acting upon each other, their total momentum remains constant unless an external force is applied. Therefore, momentum can neither be created nor destroyed.“
Suppose two objects (two balls A and B, say) of masses mA and mB are travelling in the same direction along a straight line at different velocities uA and uB respectively .
And there are no other external unbalanced forces acting on them. Let uA
As seen in Fig., uB and the two balls collide with one another. The force FAB is applied by ball A to ball B during the collision, which lasts for time t, and the force FBA is applied by ball B to ball A.
Assume that vA and vB represent the respective velocities of the two balls A and B following their collision.