This law state that ” The rate of change of linear momentum of a body is directly proportional to the applied force and the change takes place in the direction of the applied force”.
Let F be the external force applied on the body in the direction of motion of the body for time interval ∆t, the velocity of a body of mass m changes from v to v+∆v.
Now, The Change in Momentum, ∆p = m∆v
If F = 1N, m = 1 kg and a = 1 m/s², then a unit force may be defined as the force which produces unit acceleration in a body of unit mass.
Relation Between Newton and Dyne
1 N = 1 kg × 1 m/s² = 10⁵ gcm/s² Or 1 N = 10⁵ dyne