2. Iraq moves to defuse war momentum Storm Gains Momentum, But Not Power, In Trek Across Gulf Group hopes to gain Momentum with improv events Push For FDA Regulation Of Tobacco Gains Momentum In Congres S MINI Maintains Winning Momentum Passenger rail projects are gaining momentum Fumbled punt turns momentum You have the momentum; the critical need is that you use that momentum and bury them in this third quarter

3. Unit Three Chapter 7 – Momentum Chapter 8 – Energy

4. Momentum: *inertia in motion *mass in motion

5. The momentum of an object is equal to the mass of the object times the velocity of the object Momentum = mass * velocity p = m * v

6. The equation illustrates that momentum is directly proportional to an object's mass and directly proportional to the object's velocity.

7. The standard metric unit of momentum is the kg*m/s.

8. Momentum is a vector quantity.

9. A large truck has more momentum then a small car going the same speed. Why?

10. But a small car going very fast can have a greater momentum then a large truck going very slow.

11. If the momentum of an object changes, either the mass or velocity or sometimes both changed. Mass usually stays the same so the velocity is usually what changes.

12. And if velocity changes acceleration occurs. What causes acceleration?

13. FORCE The greater the force acting on the object the greater the change in velocity and therefore the greater momentum change

14. How long the force acts upon an object is important. Brief time, brief force  small change Same force over an extended period of time  greater change

15. So………

16. Both force and time are important in changing momentum

17. The quantity: Force x time interval is call impulse Impulse = F x t (Units – N · s)

18. Impulse = change in momentum so……. F x t = Δ(m x v)

19. Increasing Momentum

20. When hitting a baseball or golf ball, you want to hit with a large force for a long time. So you want an impact force to be great. That’s why your coaches always yell at you to “follow through.”

21. Decreasing Momentum To stop a car you can hit a concrete wall or a haystack. You will be decreased by the same impulse whichever you choose. Which one do you want? Why?

22. (Overhead) The same impulse does not mean the same amount of force or the same amount of time. It means the same product of force and time.

23. By hitting the haystack the impact time (the time during which your momentum is brought to zero) is extended. A longer impact time decreases the force of the impact and decreases the deceleration.

24. More examples: When you catch a baseball with your bare hand, do you just catch it or do you give a little when you catch it?

25. When you jump off of something do you land stiff legged or do you bend your knees?

26. Air bags in cars…. extend the time required to stop the momentum of the driver and passenger and therefore decrease the force

27. a. Boxer moves away from the punch  increases time of impact  reduces force of impact b. When boxer moves toward the punch  time of impact is reduced  Force of impact is increased

28. Bouncing

29. Impulses are greater when objects bounce

30. The impulse required to bring an object to a stop and then to “throw it back again” is greater than the impulse required to merely bring the object to a stop.

31. If a flower pot falls on your head you may be in trouble. If it bounces you might be in serious trouble. Why?

33. Conservation of Momentum

34. Newton’s Second Law says To accelerate an object a net force must be applied.

35. For Momentum: To change the momentum of an object, exert an impulse on it

36. Either the force or impulse has to come from outside the object

37. Pushing on the dashboard of your car does not change the momentum of the car. (internal force) A push on the outside of your car could change the momentum of the car. (external force)

38. If no external force or impulse is applied then there can be no change in momentum.

39. Again………

40. Momentum is a vector  meaning it has magnitude and direction

41. So, because momentum is a vector, it can be canceled out or brought to equilibrium.

42. Canon – Cannonball system

43. The canon fires the cannon ball. The force on the cannonball is equal to the force pushing back on the canon (3 rd law) so the net force is zero. If no net force or net impulse acts on a system, the momentum of that system does not change.

44. Conserved: when momentum, or any other quantity, does not change.

45. Law of Conservation of Momentum In the absence of an external force, the momentum of a system remains unchanged.

46. Collisions

47. Net Momentum before equals Net Momentum after

49. Elastic Collisions: When objects collide without being permanently deformed and without generating heat.

51. Inelastic Collisions: When colliding objects become tangled or crumpled and generate heat

53. You decide…. Elastic or Inelastic?

59. Net (mass)(Velocity) Before = Net (mass)(velocity) After

60. Friction at the point of impact is negligible so it is not taken into account

61. Friction produces an impulse to decrease momentum after a collision……..