1. Physics Chapter 6
Impulse and Momentum

2. Momentum Momentum depends on… The property of momentum… Mass Velocity
Momentum = Mass x Velocity
The property of momentum…
Variable: p
Unit:
Scalar or Vector?
Equation: p = mv

3. Example #1
Which has more momentum, a 1-ton car moving at 100 km/h or a 2-ton truck moving at 50 km/h?

4. Example #2
How fast would a 18 kg kid on a tricycle have to go in order to have the same momentum as a 55 kg car traveling at 25 m/s?

5. Impulse
Momentum can change. Most often, the mass of an object remains the same, while the velocity changes.
Dp = mDv
Dv  acceleration a = Dv/t  Dv=at
Dp = mDv becomes Dp = m x a x t
Dp = Force x time = Ft
This is called Impulse
I = Ft F

6. Example #3
If a baseball bat applies a 22-N force to a baseball for 0.13 s, what is the impulse experienced by the ball?

7. Impulse & Momentum Impulse equals a change in momentum I = Dp
Variations
Ft = mDv
Ft = mvf – mvi
I = mDv
I = mvf – mvi
Ft = Dp

8. Example #4
What is the impulse needed to stop a 10-kg bowling ball moving at 6 m/s?

9. Example #5
A car crashes into a wall at 25 m/s and is brought to a rest in 0.1 s. Calculate the average force exerted on a 75-kg test dummy by the seat belt.

10. Impulse & Momentum Increasing Momentum  Examples: mDv = Ft
Increase the time to increase the velocity
Examples:
Follow through in sports
Basketball shoot
Baseball hit
Soccer kick
Golf swing
Long-range cannons have long barrels

11. Impulse & Momentum Decreasing Force  Examples: mDv = Ft
Increase the time to decrease the Force
Examples:
Catching
Egg toss
Water balloon
Football
Cars: Crumple Zones & Air Bags
Roll with the punches
Mighty Ducks
Jumping and landing (sprung floors)
Running Shoes
Any padding
Bungee Jumping

12. Problems Review Questions Exercises Problems 1-11, 13 1-4, 6, 9, 10
1, 2, 5

13. Conservation of Momentum
Newton’s Second Law…
If we want an object to accelerate, we must apply a force.
Impulse and Momentum…
If we want a change in momentum, we must apply an impulse.
In both cases, the force or impulse must be exerted on the object or any system of objects by something external.

14. Conservation of Momentum
If we define the system to include all the objects we want to study…
 all forces become internal;
 there can be no impulse;
 no impulse means no change in momentum!
When a physical quantity remains unchanged during a process, that quantity is said to be…
CONSERVED.

15. Collisions Momentum is conserved  Three types of collisions…
Momentum before = Momentum after
Three types of collisions…
Elastic  objects rebound off each other without lasting deformation.
Inelastic  objects are deformed by the collision; think car crashes.
Perfectly inelastic  both objects stick together

16. Example #1a
The blue car is moving at 10 m/s, with a mass m. The orange car, also mass m, is at rest. If the freight cars are coupled together by the collision, what is their combined velocity?
v = 0
v = 10 m/s
v = ?

17. Example #1b
If the freight cars in the previous example do not couple and experience an elastic collision, what is the velocity of the orange car?
v = 0
v = 10 m/s
v = ?
v = 0

18. Example #2
Two trucks with equal masses, m, experience a head on collision. After collision, the coupled wreck remains at the point of impact with zero momentum. If the green truck was moving at 10 m/s, how fast was the red truck moving?
v = ?
v = 10 m/s
v = 0

19. Example #3
A 3 kg object traveling at 5 m/sec collides head-on with a 2 kg object that is traveling at 2 m/sec in the opposite direction. What is the velocity of the second object after the collision if the first object is moving at 1 m/sec? 6

20. Problems
Review Questions
18-23
Exercises
13, 21
Problems
6-10