Momentum is the product of the mass and velocity of an object. For example, a large rock falling down a hill has a larger momentum than a small rock falling down the same hill. Like velocity, momentum is a vector quantity. The equation is as followed:

P=mv

For example, if two particles interact, the forces between them are equal and opposite. If the particles are numbered 1 and 2, the second law states that F1 = dp1/dt and F2 = dp2/dt, therefore:

(dp_1 )/dt= -(dp_2)/dt

And

d/dt ( p_1+ p_2 )= 0

If the particles velocities are u1 and u2 before the interaction and v1 and v2 after the interaction then:

m_1 u_1+ m_2 u_2= m_1 v_1+ m_2 v_2

This law is an exact law which holds true in all situations.

Momentum is a conserved quantity in a closed system. It was first postulated in Newtonâ€™s laws of motion. It is now used in many different aspects of scientific calculations. Conservation of momentum is used in collisions, vacuums, quantum mechanics and many more. It has led to many discoveries in the field of physics.