2. The Law of the Conservation of Momentum

3. Conservation of Momentum The law of conservation of momentum states when a system of interacting objects is not influenced by outside forces (like friction), the total momentum of the system cannot change. If you throw a rock forward from a skateboard, you will move backward in response.

4. How did my sister get this huge bump and black eye?

5. The Law of the Conservation of Momentum states… The total momentum of all objects interacting with one another remains constant regardless of the nature of the forces between the objects. The total momentum of a system will stay the same before and after a collision.

6. Can you try to explain my sister’s black eye using the “Law of the Conservation of Momentum”?

7. The Law of the Conservation of Momentum states… The total momentum of all objects interacting with one another remains constant regardless of the nature of the forces between the objects. The total momentum of a system will stay the same before and after a collision.

8. Why does Mr Stickfigure on the ice move backwards? Before CollisionAfter Collision Momentum = zero (not moving) p total = 0kgm/s Momentum = zero p total = 5kgm/s + (-5kgm/s) p total = 0kgm/s +p -p p = -5 kgm/sp = 5 kgm/s

9. Why does Mr Stickfigure move backwards? Answer the Question – Mr Stickfigure moves backwards because he threw the ball forward. Explain the Relationship – The Law of the Conservation of Momentum states that the total momentum of a system must stay the same before and after. Before the ball and Mr Stickfigure had a total momentum of zero, so after the total momentum needed to stay zero. Support with Data/Observations – When the ball moved forward it had a positive momentum, so Mr Stickfigure needed a negative momentum to cancel it out. This is why he moved backwards.

10. Why do both skaters move after? Before p total = 0 kgm/s (not moving) After p total = 0 kgm/s

11. Answer the Question – Both skaters move after in order to conserve momentum. Explain the Relationship – The Law of the Conservation of Momentum states that the total momentum of a system must stay the same before and after. Before the two skaters had a total momentum of zero, so after the total momentum needed to stay zero. Support with Data/Observations – When they push against each other one moved forward and had a positive momentum, so the other needed to move backwards to have a negative momentum, so the total momentum stayed zero. Why do both skaters move after?

12. “recoil” Recoil is a term that refers to moment when a gun moves backwards after it is shot. Recoil happens because everything must follow “The Law of the Conservation of Momentum”!!!

13. Why a gun “recoils”. The total momentum before was zero So the total momentum after has to be zero The gun moves with a negative momentum because the bullet moves with a positive momentum and they cancel out, the total momentum stays zero. This explains my sister’s face!!! She shot her gun without positioning herself correctly and when the gun recoiled it hit her!!!!

14. 3 Types of Collisions Elastic Inelastic Perfectly Inelastic

15. Elastic or Inelastic? An elastic collision loses no energy. The deform- ation on collision is fully restored. In an inelastic collision, energy is lost and the deformation may be permanent. (Click it.)

16. Elastic A collision in which two objects move separately with different velocities, but not permanent deformation

17. Inelastic A collision in which two objects deforms so that the objects move in the same direction but with different final velocities after colliding.

18. Perfectly Inelastic A collision in which two objects stick together and move with the same velocity after colliding.

19. For each of the following examples, identify the type of collision…

20. Perfectly Inelastic

22. Elastic

23. Perfectly Inelastic

24. Inelastic

25. Perfectly Inelastic

26. Elastic

27. Explain why the final velocity of the moving object “makes sense” in order to conserve total momentum. After the collision the 1 st ball transferred its momentum to the 2 nd ball. Since the balls have the same mass, the velocity of the second ball should be the same as the first in order to conserve momentum.

28. Explain why the final velocity of the moving object “makes sense” in order to conserve total momentum. After the collision, the 1 st block transferred its momentum to the 2 nd block. Since the 2 nd block has more mass, the velocity should be less, in order to conserve momentum. The block is 2x bigger, it is ½ as fast.

29. Explain why the final velocity of the moving object “makes sense” in order to conserve total momentum. After the collision the cart and McDonald are moving. Since there is more mass, there should be less velocity to conserve momentum.

30. Easy Problem Solving A 50.0kg girl jumps into a 100kg raft at rest on the water. If the velocity of the girl is 4.00m/s as she jumps, what is the final velocity of the girl and the raft? G R G R m G = 50.0kg V G = 4.00m/s m R = 100kg V R = 0m/s m G = 50.0kg m G V G + m R V R = (m G + m R )V f 200kgm/s = (150kg)V f 1.33m/s = V f 1 st Draw a Picture BeforeAfter m R = 100kg V f = ? (50.0kg)(4.00m/s)+(100.0kg)(0m/s) = (50.0kg +100kg)(V f )

31. Easy Problem Solving A 63.0kg astronaut throws a 5.0kg hammer in a direction away from the shuttle with a speed of 18.0m/s, pushing the astronaut back to the shuttle. Assuming that the astronaut and hammer start from rest, find the final speed of the astronaut after throwing the hammer. 1 st Draw a Picture BeforeAfter A H A H m A = 63.0kg V A = 0m/s m H = 5.0kg V H = 0m/s m A = 63.0kg V A = ? m H = 5.0kg V H = 18m/s m A V A + m H V H = m A V A + m H V H (63.0kg)(0m/s)+(5.0kg)(0m/s) = (63.0kg)V A + (5.0kg)(18.0m/s) 0kgm/s = (63.0kg)V A + 90.0kgm/s -90.0kgm/s = (63.0kg)V A -1.43m/s = V A +90kgm/s -90kgm/s

32. Easy Problem Solving 1 st Draw a Picture BeforeAfter 1 2 A H m 1 = 15.0kg V 1 = 4.0m/s m 2 = 6.5kg V 2 = -2.0m/s m 1 = 15.0kg V f = ? m 2 = 6.5kg m 1 V 1 + m 2 V 2 = (m 1 + m 2 )V f (15.0kg)(4.0m/s)+(6.5kg)(-2.0m/s) = (15.0kg + 6.5kg)(V f ) 60kgm/s + (-13.0kgm/s) = (21.5kg)V f 47.0kgm/s = (21.5kg)V A 2.19m/s = V A A 15.0kg cart moving to the right with a speed of 4.0m/s collides with a 6.5kg cart moving to the left with a speed of 2.0m/s. If the carts stick together, find the final speed of the two carts. 60kgm/s -13.0kgm/s = (21.5kg)V f

33. Key Concepts Elastic m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f Inelastic m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f Perfectly Inelastic m 1 v 1i + m 2 v 2i = (m 1 + m 2 )v f “Starts from rest” V i = 0m/s “Stops” V f = 0m/s