Impulse and Momentum

Introduction Most interactions between two objects take place in an instant Studying how these objects behave before and after the interaction, allows us to study the interaction itself.

Interactions

Velocity of the object changes(from 0 to Velocity of the object changes(from 0 to ??) so there must be an acceleration. Therefore there must be a ….. Force The force changes as contact occurs.

Using 2nd Law F=ma a = ∆v/ ∆t Therefore F = m ∆v/ ∆t F ∆t = m ∆v

Impulse F ∆t is called the impulse. Reference Table : J = F ∆t This is the average force on an object multiplied by the time over which they interact. Vector Units are Ns Can be found by the area under a F vs. t graph

Momentum mv is the momentum of an object ∆p = m ∆v or p=mv Also a Vector Units are kg m/s which is equal to a Ns p is for a given instant of an object

Impulse Momentum Theorem ∆p = Ft The change in an objects momentum is equal to the impulse given to the object. A large force over a short period of time can produce a large change in momentum. A small force acting over a long period of time can produce the same change.

Practical Use When a car crashes, the momentum of the driver goes to zero. Steering wheel: F t Air Bag: F t

Practice An 800kg car is traveling with a velocity of 25m/s to the east. What is the momentum of the car?

If the same car stops in 10. 0s If the same car stops in 10.0s. What is the average force applied by the brakes to the car?