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Newton’s Third Law of Motion

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

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Newton’s Third Law of Motion

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  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)

  3. 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).

  4. (Force) (Acceleration) = (Mass) 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 3rd 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 2nd Law.

  5. Check Yourself 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.

  6. Action and Reaction Common expression of 3rd 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.

  7. Action-Reaction Pairs

  8. 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? Mr. B Mr. A Action Reaction Mr. B has more mass than Mr. A Mr. A goes faster (greater acceleration) since his mass is less.

  9. 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? Mr. B Reaction Mr. A Action Action Reaction Twice the force so twice the acceleration (by 2nd Law)

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

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