1. Impulse A change in momentum

2. How to change momentum Any object that has momentum is going to be hard to stop To stop an object a force needs to be applied to the object, against the object’s motion and for a certain period of time It takes a greater force or amount of time to stop an object with a large momentum The momentum of the object is changed since the velocity is changed

3. Changes in momentum in real life In a football game, the defensive players stop the momentum of the offensive players so the offense does not score When driving, we apply the brakes which is a force to stop the car and change the velocity of the car

4. Impulse Impulse = change in momentum The formula for impulse is: Impulse = Δp = F * t Δp = impulse in N*s (change in momentum) F = force in Newtons (N) t = time in seconds (s) reminder p = mv so Δp = m *Δv

5. Collision In a collision, the object experiences an impulse The impulse is equal to the change in momentum The object will speed up or slow down or change direction due to the force for a given amount of time

6. Elastic Collisions When a ball rebounds off a wall there will be a change in velocity and a change in momentum, that is the impulse The greater the rebound effect the greater the acceleration, momentum change and impulse A rebound has direction and speed change

7. Elastic Collisions If a rebound has the same speed (and momentum) before and after the collision, it is called an elastic collision Elastic collisions usually have a large velocity change, a large momentum change and a large force

8. Practice – fill in the blanks p = mv Δp = F * Δt Δp = m * Δv Force F Time t Impulse Δp Momentum Change Δp Mass m Velocity Change Δv NsN*skg*m/skgm/s 10.01010-4 20.100-4010 30.010-20050 4-20000-200-8 5-2001.050

9. Sample Problem A.50kg cart is pulled with a 1N force for 1 second and a.50kg cart is pulled with a 2N force for.50seconds. Which cart has the greatest acceleration and impulse? Cart 1 a = F/m so a = 1N/.50kg = 2 m/s 2 impulse = F * t = 1N * 1s = 1N*s cart 2 a = F/m so a = 2N/.5kg = 4m/s 2 impulse = F * t = 2N *.5s = 1N*s Cart 2 has a greater acceleration but both carts have the same change in momentum or impulse

10. Sample Problem 2 A hockey player applies an average force of 80N to a.25kg hockey puck for a time of.10 seconds, what is the impulse of the hockey puck? Δp = F * t Δp = 80N x.10s = 8N*s