1. On the highway of life, are you the bug or the windshield?

2. Bug hits windshield

3. The force on each is… The same- Newton’s third law says you can only exert back as much force as is exerted on you.

4. The length of time of impact is… The same- It would be impossible for the bug to hit the windshield for 2 seconds while the windshield hits the bug for 3 seconds.

5. The change of velocity on each is… Very different! On the car, hardly noticeable. For the bug very noticeable. The bug slows down, stops and reverses direction to match the car.

6. The momentum before and after… The same - momentum is conserved in a collision.

7. What about a BIGGER BUG – say the size of a deer?

8. The force on each is… The same- Newton’s third law says you can only exert back as much force as is exerted on you.

9. The length of time of impact is… The same- It would be impossible for the bug to hit the windshield for 2 seconds while the windshield hits the bug for 3 seconds.

10. The change of velocity on each is… Different. The car, slows down noticeably; the bug slows down, stops and then reverses direction.

11. So why does the bug go splat, but a windshield doesn’t?

12. It’s only a small force when a bug hits the windshield. It only takes a small force to kill a bug. That same size force won’t hurt the windshield.

13. The difference? The size of the force, and momentum. For the small bug, the less force, change in momentum; the bigger the bug the more of each.

14. What if the bug is the same mass and same speed as a car like another car?

15. They stop

16. Momentum Momentum – the product of mass and velocity Momentum (p) = mass (m) x velocity (v) Units for momentum are kgm/s Momentum is a vector (DIRECTION IS IMPORTANT!) Law of Conservation of Momentum – in a closed system (no external forces such as friction), the total momentum remains constant We often care about momentum during collisions Total momentum before = Total momentum after Any momentum lost by one object will be gained by the other Some collisions are elastic – objects bounce off each other Some collisions are inelastic – objects don’t bounce off

17. Momentum An object’s momentum is directly related to both its mass and velocity. Momentum = mass x velocity For some reason, maybe because mass is designated as “m” in formulas, momentum is designated as “p”. Therefore: p = mv The unit for mass is kg, the unit for velocity is meter/second, therefore the unit for momentum is kg m/sec Conservation of Momentum: –When two or more objects interact (collide) the total momentum before the collision is equal to the total momentum after the collision

18. Momentum – 2 moving objects During this collision the speed of both box cars changes. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.

19. Momentum – 1 moving object During this collision the speed red car is transferred to the blue car. The total momentum remains constant before & after the collision. The masses of both cars is the same so the velocity of the red car is transferred to the blue car.

20. Momentum – 2 connected objects After this collision, the coupled cars make one object w/ a total mass of 60,000 kg. Since the momentum after the collision must equal the momentum before, the velocity must change. In this case the velocity is reduced from 10 m/sec. to 5 m/sec.