Impulsive Forces: The force which act on a body for a short time are known as Impulsive forces.
For eg. Hitting a ball with bat fining a gun etc.
An Impulsive force doe snot remain constant but changes, firstly from zero to max and then from max. to zero.
So it is not possible to measure the exact value of force. Hence in such cases, we measure the total effect of force known as Impulse.
So Impulse of a force is defined as the measure of total effect of force. It is given by the product of force and time.
Impulse = F´t
Acc. To Newton’s 2nd Law
F = dp/dt
Þ Fdt = dp
Integrating both sides with in the respective limits and solving, we get:
F[t]ot = [p]p1p2
F[t – o] = [p2 – p1]
Ft = p2 – p1
Impulse is a vector quantity and it is also measured by the total change in the linear momentum. Its direction is same as that of force.
The dimension formula for Impulse is [MLT-1] The S.I unit of Impulse is N sec and C.G.S unit is dyne sec.
The equation Impulse = Change in momentum is also known as the Impulse momentum Theorem.
(i) A cricket player lowers has hands while catching the ball : by doing so the time of impact increases and hence the effect of force decreases.
(ii) When a person falls from a certain height on floor, he receives more injuries as compared to falling on a heap of sand. It is because the Cemented floor does not yield whereas the sand yield there by increasing the time of impact hence decreasing the impact of force.
(iii) The shock absorbers provided in the vehicle helps to travel smoothly on an uneven road. It is because the shockers increases the time of impulse which reduces the force.