1. Would you rather be hit by a tennis ball or a bowling ball?

2. To answer the question, you would want to consider mass but also velocity. That is momentum.

3. momentum = mass x velocity Momentum is inertia in motion. Ex: What is the momentum of a 10 kg bowling ball moving at 20 m/s ? p = m x v p = 10 kg x 20 m/s p = 200 kg m/s

4. What would you have to change to change momentum? To change momentum, you can change mass or velocity. What is the name for a change in velocity? Acceleration.

5. What does it take to cause an acceleration? A force is needed to cause an acceleration. The longer a force is applied, the greater the change in momentum.

6. Baseball Golf Soccer Many sports involve a change in momentum.

7. Impulse is a physics term that relates a force and the amount of time it is applied. force x time = impulse Example: What impulse is applied to a baseball if the batter uses a 50 N force for 0.2 seconds?

8. F = 50 N t = 0.2 s Impulse = force x time 50 N x 0.2 s = 10 Ns

9. It is impulse that causes a change in momentum. So Ft = ∆ p Ft = p f - p i Ft = mv f - mv i

10. What is the change in momentum if a 1000 kg car accelerates from 20 m/s to 50 m/s? 30,000 kg m/s

11. A 5 kg mouse is moving at 10 m/s. If he comes to a stop, what was his change in momentum? m = 5 kg v i = 10 m/s v f = 0 m/s final momentum = 0 kg m/s initial momentum = 50 kg m/s ∆ p = 0 kg m/s – 50 kg m/s ∆ p = - 50 kg m/s The negative indicates a loss of momentum.

12. Example: A 20 kg object starts at rest. In 5 s, it has a speed of 100 m/s. How much force was used? 400 N

13. Give examples of a moving object coming to a rest. How could you minimize the force felt by these objects? Give examples of ways in which the time for an object to stop is increased. Airbags

14. A 800 kg car is moving at 30 m/s. The driver slams on the breaks. It takes the car 3 s to stop. What force did the brakes supply? - 8000 N The negative indicates the force is in the opposite direction of the motion. If the driver of the car above eased on the breaks for 30 s to come to a stop, how much force did the breaks supply? - 800 N

15. Example: A 40 N force is applied to a 5 kg object for 10 s. If the object was initially moving at 20 m/s, what is its new speed? 100 m/s

16. Conservation of Momentum Physics Definition: In the absence of an external force, the momentum of a system remains unchanged. A system can be one or more objects. Example of internal forces: explosions collisions

17. The recoil of a gun is a good example of conservation of momentum. Gun Recoil Another Example On A Larger Scale

18. Inelastic Collisions In an inelastic collision, the objects involved in the collision stick together after they collide. An Example

19. Conservation Of Momentum For Collisions The momentum before a collision is equal to the momentum after a collision. momentum before = momentum after

20. A 5 kg object moving at 10 m/s collides with a 10 kg object at rest. After the collision, the 5 kg object stops moving. What is the speed of the 10 kg object?

21. Inelastic Example A 1000 kg car moving at 20 m/s strikes another 1000 kg car at rest. Afterwards, they stick together. What is their speed? V = 10 m/s

22. 4/13 Reading #12 (The last one!) 4/19 Great Adventure $ due 4/19 Quiz 1 4/27 Quiz 2 4/27 Formal Lab (Hooke’s Law or Hotwheels) 5/3 Test 1

23. 5/11 Progress Reports open 5/14 Junior Prom 5/17 Progress Reports Go Home 5/19 Quiz 3 5/21 Great Adventure 6/1 Quiz 4

24. 6/4 Senior Prom 6/9 Test 2 6/16 Exams Begin 6/23 Graduation

25. A 0.50 kg object is at rest. A 3.00 N force to the right acts on the object during a time interval of 1.50 s. What is the new speed of the object? 9 m/s

26. A 2500 kg car travelling to the north is slowed down uniformly from an initial velocity of 20.0 m/s by a 6250 N braking force acting opposite the car’s motion. What is the car’s velocity after 2.50 s? 13.8 m/s

27. A 6.00 g bullet moving at 375 m/s is fired into a stationary 5.50 kg wooden block which is at rest on a flat surface. After moving 7.00 cm, the block and the embedded bullet come to a rest. What is the coefficient of friction? 0.12

28. Ballistic Pendulum

29. A 7.50 g bullet moving at 420 m/s is fired into an 8.00 kg ballistic pendulum. How high does the pendulum rise? 0.776 cm

30. An elastic collision is one where both the momentum and the kinetic energies are conserved. A 4.0 kg bowling ball sliding to the right at 8.0 m/s has an elastic head-on collision with another 4.0 kg bowling ball initially at rest. The first ball stops after the collision. Verify that kinetic energy is conserved.

31. Calculate the recoil velocity of a 4.0 kg rifle that shoots a 0.050 kg bullet at a speed of 280 m/s. -3.5 m/s

32. A ball of mass 0.440 kg moving with a speed of 4.50 m/s collides head on with a 0.220 kg ball at rest. If the collision is perfectly elastic, what will be the speed and direction of each ball after the collision? 1.50 m/s and 6.00 m/s

33. A 1500 kg car traveling east with a speed of 25.0 m/s collides inelastically at an intersection with a 2500 kg van traveling north at speed of 20.0 m/s. Find their velocity after the crash. 15.6 m/s @ 53.1 0 N of E