1. NEWTON’S THIRD LAW THE LAW OF INTERACTION

3. TEST YOURSELF Hammer hits nail,____________ Hand punches wall, ___________ Book pushes down on table top,________ Bat hits ball, _____________ Car pushes road, _____________

4. NEWTON’S COMMON SENSE Newton realized that nature was symmetrical. That is, things occurred in pairs. He said that forces also occurred in pairs

5. F 1,2 = -F 2,1 For every action there is an equal and opposite reaction

6. EARTH AND ROCK The earth pulls on a 1kg object with how much force? Does the 1 kg object pull on the Earth? If so, how much?

7. A NUMERICAL EXAMPLE. For every action there is an equal and opposite reaction Lady bug Mass = 3.5 g Velocity = 4.8 m/s, south F supplied by the car = 10 N Nissan Titan -Mass = 2289 Kg (5000 lb.) -Velocity = 24.6 m/s (55 mph), North -F supplied by the bug__________N

8. IF THE FORCES ARE EQUAL AND OPPOSITE, THEN WHY DON’T THEY CANCEL EACH OTHER OUT? The reason they don’t cancel out is because they act on different objects. For example: foot kicks ball. Ball kicks foot.

9. GUN EXAMPLE A gun with a mass of 1.35 kg fires shot with a mass of 45 g. If the recoil force is - 16.2 N, what are the accelerations of the gun and the shot?

10. SOLUTION (ASSUME THE SHOT IS MOVING TO THE RIGHT AND THIS IS THE POSITIVE DIRECTION) Shot Fnet = ma Fnet/m = a +16.2 N/.045kg = a a = 360 m/s 2 Gun Fnet = ma Fnet/m = a -16.2 N/1.35 kg = a a = - 12 m/s 2 Would you want to shoot a huge (massive) bullet with a small (less massive) gun?

11. NEWTON’S 3 RD LAW IN ZERO GRAVITY What would it be like?? (5 min)