Impulse and Momentum

(a) We know that the velocity v m s^-1 of a body of mass m kg moving with a constant

acceleration a m s^-2 for time t seconds is given by

v = u + at, where u is the initial velocity.

→ mv = mu + mat

→ mat = mv - mu.

Newton's Second Law states that F = ma

→ Ft = mat

→ Ft = mv - mu.

Note that F must be constant since a is constant.

(b) We define the impulse, I, of a constant force F N acting for a time t seconds to be

I = Ft Newton-seconds (Ns).

(c) We define the momentum of a body of mass m kg moving with velocity v m s^-1 to be 

mv kg m s^-1.

(d) The equation I = Ft = mv - mu of paragraph (a) can now be thought of as

Impulse = Change in Momentum.

N.B. Impulse and Momentum are vectors.