1. A Second Look at Newton’s Lawby
Dick Heckathorn
C.V.C.A. Physics
17 November 2K + 4

2. A car at rest possesses:
Amount identified by:

3. A moving car possesses:

4. A moving car also possesses:

5. Moving car has
mass and velocity
Car at rest has mass
velocity = 0

6. What happens when the car starts from rest and achieves some velocity?
The car’s momentum:
Increases

7. What happens when the car moving at some velocity comes to rest?
The car’s momentum:
Decreases

8. What causes the increase or decrease in momentum?
How big is the force?

9. Let’s examine Newton’s 2nd Law
Know
Know
Then
And

10. Newton’s 2nd Law
Will call:

12. The amount of impulse is the change in momentum.
Newton’s 2nd Law
Will call
The amount of impulse is the change in momentum.

13. Newton’s 2nd Law What causes a change in momentum?
How big is the force? If
Then If
Then

14. Newton’s 2nd Law What are the units? How do these units compare?
Same - Same

15. Summary
If a car changes velocity from zero to some velocity, the car’s momentum increases.
It is likewise true for a moving object that comes to a stop, the car’s momentum decreases.

16. Does the momentum of a 2000-kg car going North at 30-km/hr equal the momentum of a 1000-kg car going West at 60-km/hr? No
Momentum is a vector quantity so to be equal, they must be the same magnitude and in the same direction.

17. Question A Mack truck has more mass than a roller skate.
Will it always have more momentum than the roller skate? No
A Mack truck at rest will have no momentum.

18. Question
Could a Mack truck and a roller skate have the same non-zero momentum.
Yes
Mack truck moving very slow and roller skate moving very fast.

19. Question
How far from the shore does an oil tanker shut off its engines to allow water resistance to stop the tanker as it comes into port?
25 kilometers

20. 18. What is the change in momentum of a 1500-kg when it changes from 20-m/s North to 20-m/s West?

21. That’s all folks!