Conservation of Momentum

1. Conservation of Momentum Collisions and Explosions

2. Review of Newton’s 3rd Law • While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?

3. Review of Part 1 Ft=mΔv

7. Conservation of Momentum • When two objects collide • Force between the 2 is the same (newton’s 3rd) • The time they collide is the same • This means the impulses are equal

8. Conservation of Momentum • Thus, since each object experiences equal and opposite impulses, it follows logically that they must also experience equal and opposite momentum changes • Think of this as a system, not individual pieces

9. Check Your Understanding • When fighting fires, a firefighter must use great caution to hold a hose that emits large amounts of water at high speeds. Why would such a task be difficult?

12. Demo • Same size carts • Small runs into large • Large runs into small

16. v = 0 What is the speed of the cannon? 200-kg cannon and 1-kg cannonball (400 m/s)

17. v = 0 0 = What is the speed of the cannon? (200)v + (1)(400) v = -2 m/s 200-kg cannon and 1-kg cannonball (400 m/s)

18. Check Your Understanding A large truck and a Volkswagen have a head-on collision. • a. Which vehicle experiences the greatest force of impact? • b. Which vehicle experiences the greatest impulse? • c. Which vehicle experiences the greatest momentum change? • d. Which vehicle experiences the greatest acceleration?

19. Conservation of Momentum Sample Problems

48. m