In

an accident which occurs in a very short period of time, the force acting on the object will be large.

From Newtons Second Law of Motion

F ! ma

As

v u a! t

v u mv mu F ! m ! t t

Also, change Hence,

in momentum = mv mu

Force =

Change of Momentum time

Note that from this formula, force is a) Directly proportional to change of momentum b) Inversely proportional to time

force is defined as the rate of change of momentum. Impulsive force is expressed as Therefore, impulse

mv mu ! t

The

impulsive force that can be seen in our daily activities area) Hitting a tennis ball b) Traffic accident on the road c) Stopping of a baseball d) Hitting a nail using a hammer

In

all the situations, the time of contact is very small and the force produced is large.

From

the equation

mv u F! t

@ Ft ! mv muImpulse, Ft = = mv mu change of momentum

Ft is equal to the change of momentum. The SI unit for impulse is newton seconds (N s) Impulse is a vector quantity. It has the same direction as the applied force Therefore, impulse,

A car with a mass of 1000 kg -1. It travels at a speed of 40 ms crashes into a wall and stops within 0.2s. Calculate the force acting on the car.

A golfer uses a golf club to hit a golf ball, causing the ball to travel with a velocity of 50 ms-1. If the mass of the golf ball is 50 g and the time of contact between the -3s, golf club and the ball is 2 10 calculate the impulsive force exerted by the golf club.

A 50 kg boy jumps over a fence away from a fierce dog. His velocity just before landing on the ground is 8 ms-1. a) Calculate the impulse when his leg hit the ground. b) What is the impulsive force on the boys legs if he takes 0.2s to stop? c) What is the impulsive force on the boys legs if he bends his legs and stops in 0.8s? d) What can be concluded on the impact of the legs if the boy landed with bended knees?