Second Law of Motion

Newton’s second law of motion states that the rate of change of momentum of a body is directly proportional to the net force acting on the body. Change in momentum of the body takes place in the direction of net external force acting on the body.

If ∆p is the change in momentum of a body in time ∆t due to a net external force F,

In SI units, m = 1 kg, a = 1 m s^–2. Then magnitude of external force

F = 1 kg × 1 ms^–2 = 1 kg ms^–2 = 1 unit of force

This unit of force (kg m s^–2) is called one newton.