1. Newton’s Third Law of Motion For every “action” there is a “reaction”

2. Newton’s Third Law of Motion Whenever an object exerts a force on a second object, the second object exerts a force of equal magnitude in the opposite direction on the first object. First Object (Hammer) Second Object (Nail)

4. Check Yourself A 2 ton car, going 60 m.p.h. losses control and hits a wall The force of impact is greatest on, the car or the wall? Force on each is equal (by Newton’s 3rd Law).

5. Check Yourself A 2 ton car, going 60 m.p.h. hits a 5 ton truck, going 20 m.p.h.. The force of impact is greatest on which vehicle, the car or the truck? Force on each is equal (by Newton’s 3 rd Law). The change in velocity (the acceleration) is greatest for which vehicle? For the car, which has less mass. By what principle of physics? By Newton’s 2 nd Law. (Acceleration) = (Force) (Mass)

6. Arnold Strongman and Suzie Small pull on opposite ends of a rope in a tug of war. The greater force exerted on the rope is by 1. Arnold. 2. Suzie. 3. Neither. The force is the same. Check Yourself

7. Action and Reaction Common expression of 3 rd Law is, For every action there’s an equal and opposite reaction. What’s an “action”? A force exerted by one object on second object. How can reaction be “equal” and “opposite”? Equal in magnitude but opposite in direction.

9. Action-Reaction Pairs

10. Demo: Mutual Attraction (cont.) If only Mr. A pulls on Mr. B then Mr. B accelerates. Reaction force of equal magnitude so Mr. A also moves. Who moves faster? Mr. A, Mr. B, or the same? Action Reaction Mr. A Mr. B Mr. A goes faster (greater acceleration) since his mass is less. Mr. B has more mass than Mr. A

11. Demo: Mutual Attraction (cont.) When both guys pull then there are two action forces and two reaction forces. If both pull with same force, how much greater is the acceleration than when only one pulls? Action Reaction Mr. A Mr. B Twice the force so twice the acceleration (by 2 nd Law) Reaction Action

12. IMPORTANT!!! Action force & reaction force NEVER cancel because they act on different objects!