Momentum

The momentum of a body is the mass of the body multiplied by its velocity.

Using Newton's equation F = ma and knowledge that a = v-u/t we find that:

F = (mv-mu)/t, or

force = rate of change of momentum

Where F is the force acting on a body of mass m which increases its velocity from u to v  in a given time t'. This means, '

Ft= mv-mu

The quantity Ft is called the impulse of the force of the body. Because the change in momentum is a vector quanity, so is the impulse and must be denoted with a positive or negative sign. In words, the impulse-momentum equation is: 'impulse= change of momentum. 'The equation shows that impulse and momentum have the same unit, i.e. Ns or Kg ms^-1.

An example of impulse is when a cricketer strikes a cricket ball with their bat. If the time that the ball is in contact with the bat is greater then the impulse must also be greater. Using this, we can see that the change in momentum will be greater, i.e the ball will move away from impact with a greater speed. On the other hand, when a cricket ball is caught its momentum is reduced to zero. Therefore if the time taken to catch the ball, i.e. the contact time, is reduced the overall force of the ball on the hand is reduced, making the catch easier.

See: Conservation of momentum