2. Unit 4: Momentum and Energy Chap. 7 Momentum

3. Which is harder to stop, a truck traveling at 55 mi/hr or a small car traveling at 55 mi/hr?  Why?

4. Which is harder to stop, a slow moving large truck or a very fast moving small car?  Why?

5. What is MOMENTUM? A. Momentum: inertia in motion B. Momentum = mass x velocity (or speed) p = m. v C. Momentum is greater if it has 1. high speed 2. large mass 3. or both

6.  What could you hypothesize if the mass of an object remained the same (same object), but the momentum changed?  Acceleration occurs (velocity increases)

7.  What causes accelerations?  Force  How do you get a large acceleration?  large force or  apply a smaller force for a longer period of time

8. Impulse  Impulse: force over a period of time  Impulse = force x time  I = F. t  The higher the impulse, the greater the change in momentum

9. Impulse  The higher the impulse, the greater the change in momentum. I =  p F. t =  (m. v)

10. Would you rather hit a brick wall or a haystack?  Why  It has to do with impulse.  The impulse would be the same BUT the force and the time that make up the impulse are not the same.  You would be in contact with the haystack longer than you would be in contact with the brick wall.

11. brick wall same impulsehaystack t. F = I= t. F t. F = I= t. F Therefore, the force of the brick wall would be greater than the force of the haystack.

12. If you jump off a lab table, should you hit the ground with your legs straight or should you bend your legs? Why?

13. Which is better, to drop a ceramic dish on the sidewalk, or on thick carpet? Why?

14. Which would be safer, a padded dashboard or a metal dashboard? Why?

15. HOW IS BOUNCING DIFFERENT?  Impulse is greater when something bounces.  There are really 2 steps when bouncing:  1. impulse to bring momentum to a stop  2. provide additional impulse to bring it back up

16. HOW IS BOUNCING DIFFERENT?  The impact force will still react the same.  1. If the impulse is over a long time, then the impact force is small.  Example - a circus net  2. If the impulse is over a short time, then the impact force is large.  Example - a body dumped from a 10 story window

17. What happens to momentum during collisions?  Conservation of Momentum  Total momentum before equals total momentum after (when there are NO outside forces acting).  In the absence of an external force, the momentum of a system remains unchanged.

18. How do we know?  Newton’s 3rd Law: for every action, there is an equal and opposite reaction.

19. Types of Collisions  ELASTIC  1. Objects hit but don’t stick together  2. Transfers momentum  INELASTIC  1. Objects hit and stick together  2. Shares momentum