1. Chapter 6 Impulse and Momentum

2. DEFINITION OF LINEAR MOMENTUM The linear momentum of an object is the product of the object’s mass times its velocity: Linear momentum is a vector quantity and has the same direction as the velocity.

3. Do these objects have the same momenta? Can these objects have the same momenta?

4. How can momentum change? Two billiard balls collide and bounce back with the same speed. Does their momenta change? Why? A toy plane on a string flies around in circles with the same speed. Is its momentum changing? Why? A rocket is leaving the atmosphere, moving at a constant velocity. Is its momentum changing? Why?

5. If velocity (or speed) of the object changes, then the object…

7. There are many situations when the force on an object is not constant and we have to talk about average force. As a result of the force applied (the bat), the momentum of the ball changed.

8. Calculate the change of momentum, in SI units, if the ball was pitched at 60 mph and pounced off the bat 70 mph. The mass of the ball is 145 g.

9. DEFINITION OF IMPULSE The impulse of a force is the product of the average force and the time interval during which the force acts: Impulse is a vector quantity and has the same direction as the average force. The unit of impulse is If the ball was in contact with the bat for 0.5 s, what was the average force delivered by the bat?

10. IMPULSE-MOMENTUM THEOREM When a net force acts on an object, the impulse of this force is equal to the change in the momentum of the object

11. Example 2 A Rain Storm Rain comes down with a velocity of -15 m/s and hits the roof of a car. The mass of rain per second that strikes the roof of the car is 0.060 kg/s. Assuming that rain comes to rest upon striking the car, find the average force exerted by the rain on the roof.

12. Conceptual Example 3 Hailstones Versus Raindrops Instead of rain, suppose hail is falling. Unlike rain, hail usually bounces off the roof of the car. If hail fell instead of rain, would the force be smaller than, equal to, or greater than that calculated in Example 2? Explain.

13. Explain the physics (Impulse – momentum theorem) behind air bags

14. Compare change of momentum for each egg if they were dropped from the same height. Compare impulses applied to each. Explain why one egg breaks and the other one doesn’t

15. Why do we instinctively squat when landing after a jump? (Explain the physics of this instinct).