1. Conservation of Momentum (in 1D) SPH4U

2. Newton’s 3 rd Law The force B exerts on A The force A exerts on B

3. Newton’s 3 rd Law

4. Note that the time for the interaction must be the same.

5. Newton’s 3 rd Law

7. The Law of Conservation of Momentum During an interaction between two objects (where there is no external net force), the change in momentum of the first object is equal in magnitude but opposite in direction to the change in momentum of the second.

8. Conservation and Impulse: Example A rubber bullet R and a metal bullet M of equal mass strike a target with the same speed. The metal bullet comes to rest inside the target while the rubber bullet bounces back. Which exerts a greater impulse on the target?

9. Conservation and Impulse: Example A rubber bullet R and a metal bullet M of equal mass strike a target with the same speed. The metal bullet comes to rest inside the target while the rubber bullet bounces back. Which exerts a greater impulse on the target? R

10. Conservation and Impulse: Example A rubber bullet R and a metal bullet M of equal mass strike a target with the same speed. The metal bullet comes to rest inside the target while the rubber bullet bounces back. Which exerts a greater impulse on the target? R – changing the momentum from [fwd] to [back] requires a greater impulse than changing momentum from [fwd] to zero.

11. Conservation of Momentum

12. “Primes” denote the velocity after interaction: v’=v 2

13. Conservation of Momentum

15. The Law of Conservation of Momentum (Version 2) During an interaction between two objects (where there is no external net force), the total momentum of the system after is equal to the total momentum of the system before.

16. Conservation: Example 1 A baseball of mass m leaves a pitching machine off mass M (where M includes the mass of the ball m ) with a speed v. What is the recoil speed of the machine after shooting the baseball?

17. Conservation: Example 1 A baseball of mass m leaves a pitching machine off mass M (where M includes the mass of the ball m ) with a speed v. What is the recoil speed of the machine after shooting the baseball? Note that total momentum before is zero.

18. Conservation: Example 1

20. Since the question asks for the (positive) speed, we would express this as:

21. Conservation: Example 2 A student of mass 75 kg is standing on a stationary raft of mass 55 kg. The student then moves toward one end of the raft at a speed of 2.3 m/s [N] relative to the water. Neglecting fluid friction, what is the velocity of the raft relative to the water?

22. Conservation: Example 2 i.e., 3.1 m/s opposite the direction of motion of the student

23. Conservation: Example 2 And the velocity of the raft relative to the student is 2.3 m/s + 3.1 m/s [back]

24. More Practice Textbook Questions: p. 243 #5, 6, 7 p. 245 #7 http://www.youtube.com/watch?v=r8E5dUnLmh4