Do Now:

1. Do Now: • When two cars collide in a car accident, do you think that their total momentum will be different then what it was before the accident?

2. Objective: • Be able to distinguish and describe the different types of collisions. • Momentum, Impulse, and Collisions Notes • Momentum and Collisions Demonstrations • Momentum Impulse Relationship in Sports. • Exit Ticket Agenda:

3. Momentum

4. MomentumCHECK YOUR NEIGHBOR When the speed of an object is doubled, its momentum • remains unchanged in accord with the conservation of momentum. • doubles. • quadruples. • decreases. Explain your answer to your neighbor.

5. MomentumCHECK YOUR ANSWER When the speed of an object is doubled, its momentum • remains unchanged in accord with the conservation of momentum. • doubles. • quadruples. • decreases.

6. Impulse • Impulseis the product of force and contact time. • Equation for impulse: Impulse = force  time = Ft • Great force for long time large impulse • Same force for short time  smaller impulse

7. ImpulseCHECK YOUR NEIGHBOR When the force that produces an impulse acts for twice as much time, the impulse is • not changed. • doubled. • increased by four times. • decreased by half. Explain your answer to your neighbor.

8. ImpulseCHECK YOUR ANSWER When the force that produces an impulse acts for twice as much time, the impulse is • not changed. • doubled. • increased by four times. • decreased by half.

9. Impulse–Momentum Relationship • The change in momentum of an object is equal to the force applied to it multiplied by the time interval during which the force is applied.

10. Impulse–Momentum Relationship • Equation: Impulse = change in momentum or Force  time =  momentum • Greater force, greater changein velocity  greater changein momentum • Same force for short time  smaller change in momentum • Same force for longer time more changein momentum

11. Impulse–Momentum Relationship • Cases of momentum changes • Increasing momentum: Apply the greatest force for the longest time to produce the maximum increase in momentum. Examples: • A golfer follows through while teeing off.

12. Impulse–Momentum RelationshipCHECK YOUR NEIGHBOR Compared to a cannonball shot from a cannon with a short barrel, a cannonball shot from a cannon with a long barrel emerges with greater speed because the cannonball receives a greater • average force. • impulse. • both of the above • neither of the above Explain your answer to your neighbor.

13. Impulse–Momentum RelationshipCHECK YOUR ANSWER Compared to a cannonball shot from a cannon with a short barrel, a cannonball shot from a cannon with a long barrel emerges with greater speed because the cannonball receives a greater • average force. • impulse. • both of the above • neither of the above Explanation: The force on the cannonball is the same for short- and long-barreled cannons. The longer barrel provides a longer time for the force to act and therefore a greater impulse. (The long barrel also provides a longer distance for the force to act, providing more work and greater KE of the cannonball.)

14. Impulse–Momentum Relationship • Cases of momentum changes (continued) • Decreasing momentum: The impulse with the longer time that decreases momentum has a smaller force. Examples: • Driving into a haystack versus a brick wall • Jumping into a safety net versus onto solid ground

15. Impulse–Momentum RelationshipCHECK YOUR NEIGHBOR A fast-moving car produces vastly different results when it hits a haystack than when it hits a cement wall. But, in both cases, the car experiences • the same change in momentum. • the same impulse. • the same force. • both the same change in momentum and the same impulse. Explain your answer to your neighbor.

16. Impulse–Momentum RelationshipCHECK YOUR ANSWER A fast-moving car produces vastly different results when it hits a haystack than when it hits a cement wall. But, in both cases, the car experiences • the same change in momentum. • the same impulse. • the same force. • both the same change in momentum and the same impulse. Explanation: Although stopping the momentum is the same whether it is done slowly or quickly, the force is vastly different. Be sure to distinguish between momentum, impulse, and force.

17. Impulse–Momentum RelationshipCHECK YOUR NEIGHBOR When a dish falls, will the change in momentum be less if it lands on a carpet than if it lands on a hard floor? (Careful!) • No, both are the same • Yes, less if it lands on the carpet • No, less if it lands on a hard floor • No, more if it lands on a hard floor Explain your answer to your neighbor.

18. Impulse–Momentum RelationshipCHECK YOUR ANSWER When a dish falls, will the change in momentum be less if it lands on a carpet than if it lands on a hard floor? (Careful!) • No, both are the same • Yes, less if it lands on the carpet • No, less if it lands on a hard floor • No, more if it lands on a hard floor Explanation: The momentum becomes zero in both cases, so both changes are the same. Although the momentum change and impulse are the same, the force is less when the time of momentum change is extended. Be careful to distinguish between force, impulse, and momentum.

19. Conservation of Momentum • In every case, the momentum of a system cannot change unless it is acted on by external forces. • A system has the same momentum both before and after the interaction occurs. When the momentum does not change, we say it is conserved.

20. Conservation of Momentum • Law of conservation of momentum: • In the absence of an external force, the momentum of a system remains unchanged. • Equation form: (Total momentum)before = (Total momentum)after

21. Conservation of Momentum • Collisions • When objects collide in the absence of external forces, Net momentum before collision = Net momentum after collision Examples: • Elastic collisions • Inelasticcollisions

22. Conservation of Momentum • An elastic collision is defined as a collision in which objects collide without permanent deformation or the generation of heat.

23. Conservation of Momentum • Moving ball A strikes ball B, which was initially at rest. • Ball A comes to rest, and ball B moves away with a velocity equal to the initial velocity of ball A. • Momentum is transferred from ball A to ball B.

24. Conservation of Momentum • An inelastic collision is a collision in which colliding objects become tangled or coupled together, generating heat.

25. Conservation of MomentumCHECK YOUR NEIGHBOR Freight car A is moving toward identical freight car B, which is at rest. When the cars collide, they couple together. Compared with the initial speed of freight car A, the speed of the coupled freight cars is • the same. • half. • twice. • none of the above Explain your answer to your neighbor.

26. Conservation of MomentumCHECK YOUR ANSWER Freight car A is moving toward identical freight car B, which is at rest. When the cars collide, they couple together. Compared with the initial speed of freight car A, the speed of the coupled freight cars is • the same. • half. • twice. • none of the above Explanation: After the collision, the mass of the moving freight cars has doubled. Can you see that their speed is half the initial velocity of freight car A?