Analysing Impulse and Impulsive Force

Analysing Impulse and Impulsive Force

Chapter 2 forces and motionImpulse and Impulsive Force

When a player kicks a football, his boot is in contact with the ball for a time t

During the time t, an average force F acts on the ball which makes the ball fly off with a momentum.

Thus, the force F, acting for a period of time t, produces a change in momentum to the ball, since the ball with a mass of m acquires velocity after the time t.Impulse and Impulsive Force

When a badminton racket hits an oncoming shuttle cock, the badminton racket delivers a large force that acts on the shuttle cock for a short time t.

The shuttle cock bounces off in the opposite direction. Again, there is a change in momentum.

The change in momentum is due to the force F acting on the object for a time t.substituteImpulseImpulsive ForceBoth impulse and impulsive force are vector quantities. Impulse is defined as the product of a force, F and the time interval, t during which force acts.

Impulse = Force Time = F tImpulseChange in momentumFRebound and Impulse

An object might rebound from a wall, or stick to it without rebounding after striking it.In which situation will the wall exert a greater impulse? A tennis ball and a piece of mud with the same mass (0.060 kg) which are moving at 9 ms-1 strike a wall. The mud sticks to the wall while the ball rebounds at 6 ms-1. Find the impulse on each object.

Solution:For the mud,Ft = mv mu= 0 0.06 (-9)= 0 + 0.54= 0.54 NsSolution:For the tennis ball,Ft = mv mu= 0.06(6) 0.06 (-9)= 0.36 + 0.54= 0.90 NsThus, a greater impulse is exerted on an object if it ________________________ after a collision.

Try this,Figure shows a 2 kg wooden block initially at rest on a smooth surface. A force of 8 N is applied on the wooden block.

If the force acts for 3 s,What is the impulse on the block?What is the velocity of the wooden block after 3 s?

A player spikes an oncoming volleyball moving towards him at a speed of 5 ms-1 to reserve its direction at a speed of 20 ms-1. The mass of the ball is 0.36 kg.

Find the impulse on the ball.If the average force acting on the ball is 300 N, how long is the time of contact between the hand and the ball?

Effects of Time on Impulsive Force

A student throw a raw egg at a high speed at a wall, and another egg against a towel held by his friends. In which case will the egg break?

The egg is stopped by the wall in a very short time interval, resulting in a large force which causes it shatter.The egg thrown against a towel falls on a few towels stacked below and does not break. The movement of the egg is stopped in a longer time interval, resulting in a small force.

In both cases, the eggs are stopped. Thus, the change in momentum is the same.To understand the effect of time in a collision, look at the following example.

Herman bends his knees upon landing.The time taken to stop his motion is 1.0 s.

Herman didnt bend his knees upon landing.The time taken to stop his motion is 0.05 sHerman (mass, m = 50 kg) jumps down from a wall. He lands on a cement ground at a velocity of 6 ms-1.

u= 6 ms-1V = 0 ms-1u= 6 ms-1V = 0 ms-1This example clearly shows that an effective way to reduce the impulsive force is to ______________________time.

The effects of time on the magnitude of the impulsive force

t largeF smallt smallF larger