Impulse refers to change in momentum. impulse is a measure of how much the momentum changes as a result of force acting on it for a period of time. In other words, when a force acts on an object for a short amount of time, impulse is the measure of how much the force changes the momentum of an object.
Impulse = Force x Change in time (F • ∆t) = Change in Momentum (m • ∆v)
In a collision, an object experiences a force for a specific amount of time that results in a change in momentum. The result of the force acting for the given amount of time is that the object’s mass either speeds up or slows down (or changes direction). The impulse experienced by the object equals the change in momentum of the object.
E.g – a football halfback running down the football field and encountering a collision with a defensive back. The collision would change the halfback’s speed and thus his momentum. Another example is the car air bag system. Airbags are in cars in order to reduce the damage to a driver or passenger during a collision.
Impulse can be calculated by the formula :
a. If force and time is given :
Impulse(N-sec)[I] = Force(N)[F] * Time Change (sec)[∆t]
b. If Mass, Final Velocity and Initial Velocity is given :
Impulse(kg.m/s)[I] = Mass(kg)[m] * (Final Velocity – Initial Velocity) (m/s)[∆v]
1. What is the impulse caused by an average force of 20 N if it acts on a ball for 4 seconds?
Impulse = Force x time change
Impulse = 20 (N) * 4(sec)
Impulse = 80 N-sec
2. If the 2.0 kg object travels with a velocity of 10 m/s before it hits the wall and 8m/s after hitting the wall, then calculate the impulse on the object ?
Impulse = Mass * (Final Velocity – Initial Velocity)
Impulse = 2 (kg) * (8 – 10) (m/s)
Impulse = 2 * (-2)
Impulse = -4 Kg.m/s
Impulse is 4 Kg.m/sec
The standard unit of measurement for Impulse is Newton.sec i.e Kg.m/sec