An object’s tendency to resist changes in motion.

1. Momentum An object’s tendency to resist changes in motion. The faster & more massive an object is, the more momentum it has. PRESS SPACE BAR TO CONTINUE

2. Conservation of Momentum • When two bodies interact, the total momentum before and after the interaction (collision) must be equal. M1V1=MaVa + MbVb PRESS SPACE BAR TO CONTINUE

3. Collision #1 Elastic Collision A moving object collides with an object at rest: • In a perfectly elastic collision (impossible), all momentum is transferred to the object at rest and it moves away at a velocity proportional to the ratio of their masses. • If they are equal in mass, the moving object comes to rest and the object formerly at rest moves away at the speed that the first ball originally had. PRESS SPACE BAR TO CONTINUE

4. Elastic collision (cont) • In a perfectly elastic collision, a ball with mass M & velocity Vo transfers its momentum to an identical ball of mass M originally at rest. The result is that the ball originally moving is now at rest. The ball formerly at rest is now moving with velocity Vo PRESS SPACE BAR TO CONTINUE

5. Elastic Collision(Unequal masses) • If the projectile is much more massive than the target, then it is only slowed down a little and the target moves away at high speed. This time, the large projectile ball is only slowed down a little & the small target ball takes off at high speed. The total momentum before is equal to the total momentum after the collision. Click to see animation PRESS SPACE BAR TO CONTINUE

6. Elastic collision (Unequal masses part II) • When a small ball collides with a large ball, the small ball returns in the opposite direction with a velocity slightly smaller and the large target ball acquires a small velocity. Click here for animation PRESS SPACE BAR TO CONTINUE

7. Collision #2: Inelastic collision In an inelastic collision, the projectile and the target stick together and then travel off at a velocity smaller than the original velocity. PRESS SPACE BAR TO CONTINUE

8. Click on red boxes for solutions PRACTICE PROBLEMS 1. How much momentum does an 800 Kg car have that travels at 4.5 m/s (~10 mi/hr)? 2. How fast would a 200 gram bullet have to travel to have the same amount of momentum as the car in #1? 3. If a 1Kg projectile travelling at 20 m/s strikes a .5 Kg target originally at rest and they stick together, with what velocity do they travel off together? 4. If a 1 Kg projectile travelling at 20 m/s strikes a 20 Kg target and the projectile moves back at 10 m/s, how fast does the target move? Remember that moving backwards is the same as having negative velocity. PRESS SPACE BAR TO CONTINUE

9. Click red buttons to return to problems Momentum = mass x velocity Solution#1 Momentum = 800 Kg x 4.5 m/s = 3600 kg.m/s Solution#2 Momentum = 3600 Kg.m/s = .2 Kg x velocity velocity = 3600 Kg.m/s ÷ .2 Kg = 18,000 m/s PRESS SPACE BAR TO CONTINUE

10. Click red buttons to return to problems M1 x V1 = M2 x V2 Solution#3 1 Kg x 20 m/s = (1 Kg + .5 Kg) x V2 V2 = 20 Kg.m/s ÷ 1.5 Kg = 13 m/s Solution#4 1 Kg x 20 m/s = 1 Kg x -10m/s + 20 Kg x Vtarget Vtarget = (20 Kg.m/s + 10 Kg.m/s) ÷ 20 Kg Vtarget = 30 Kg.m/s ÷ 20 Kg = 1.5 m/s PRESS SPACE BAR TO CONTINUE

11. Press the spacebar to finish Now you try 1. How much momentum does a 20 gram spitball travelling towards a teacher at 3 m/s have? 2. If a 100 Kg linebacker running at 5 m/s hits a 60 Kg quarterback and slows down to 1 m/s, how fast does the quarterback fly back? 3. If the same 100 Kg linebacker going 5 m/s hits a 60 Kg quarterback and “wraps him up” and they travel backwards together, at what velocity do they go back? 4. So why do football coaches tell their defense to “wrap up” when they hit? 5. If your teacher (65 Kg of solid muscle) stands on a skateboard and throws an 8 Kg bowling ball at 3 m/s, how fast will he go in the opposite direction?

12. Projectile > Target Click to return

13. Target > Projectile Click to return