1. 12.3 Newton’s Third Law of Motion and Momentum
1. What is Newton’s third law of motion?
Whenever one object exerts a force on a second object, the second object exerts a force on the first object.

2. 12.3 Newton’s Third Law b. Known as Law of Action and Reaction

3. 12.3 Newton’s Third Law c. Action & Reaction Forces:
Always occur in as a pair.
The forces applied to different objects.
The forces are present even when there is no motion.
4) Don’t cancel each other out because the action and reaction forces do not act on the same object.

4. Momentum
2. What is needed for an object to have a large momentum? a. A product of an object’s mass and its velocity.

5. Momentum b. Property of all moving objects.
c. Momentum = mass x velocity
p = m x v
(kg) (m/s)
d. SI unit for momentum is kg  m/s
(Momentum has magnitude and direction)

6. Momentum
e. If there is an increase in mass or velocity, then there will be an increase in the object’s momentum. f. An object has a large momentum if the product of its mass and velocity is large.

7. Momentum
g. Momentum Problems 1) In 1996, Michael Johnson ran m in s. Johnson’s mass at the time of his record-breaking run was about 77 kg. What was his momentum at his average speed? Work: Answer:

8. Momentum
2) A pitcher in a professional baseball game throws a fastball, giving the baseball a momentum of 5.83 kg  m/s. Given that the baseball has a mass of kg, what is its speed in km/h? Work: Answer:

9. Momentum
3) Although larger than the Atlantic walrus, the Pacific walrus can swim with a speed of about 9.7 m/s. If the momentum of a swimming walrus is 1.07 x 104 kg  m/s, what is its mass? Work: Answer:

10. Conservation of Momentum
How is momentum conserved?
a. Law of Conservation of Momentum:
If no net force acts on a system, then the total
momentum of the system does not change.
b. System must be closed which means other objects
and force cannot enter or leave a system.

11. Conservation of Momentum
c. In a closed, system, the loss of momentum of one object equals the gain in momentum of another object-momentum is conserved.

12. Conservation of Momentum
Different closed systems where momentum is conserved.
1. Both cars are moving, collide, and bounce off each other.

13. Conservation of Momentum
2. One car is moving, collide, bounce off each other.

14. Conservation of Momentum
3. One car is moving, collide, then the cars stick together.

15. 12.3 Assignment
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