1. 6-3 INTERACTION FORCES

2. Identifying Interaction Forces  “For every action, there is an equal and opposite reaction”  What is an action, what is a reaction, and why are they equal

3. Catching a ball  Ball is thrown and then caught by a person  Two systems involved???  Hand on ball = F hand on ball  Ball on hand = F ball on hand  F A on B & F B on A  Called action-reaction pairs

4. Misconception  One force causes action on another: NOT TRUE  Force of the hand on the ball DOESN’T cause the ball to exert a force on the hand.  The two forces exist together or not at all

5. Newton’s 3 rd Law  Interaction pair  Two forces that are in opposite directions and have equal magnitude  Force of the hand on the ball is equal in magnitude and opposite in direction to the force of the ball on the hand  3 rd Law  All forces come in pairs  F A on B = -F B on A

6. Problems  You lift a bowling ball with your hand, accelerating it upward. What are the forces on the ball? What are the other parts of the action-reaction pairs? On what objects are they exerted?  Force of hand on ball, Fg of earth’s mass on ball  Force of ball on hand, Fg of ball’s mass on earth  Force of feet on earth, force of earth on feet

7. Four Fundamentals  Given in student power points

8. Tension of Ropes  Rope holding up a bucket  F T(top on bottom)  F T(bottom on top)  Interaction pair: equal and opposite

9. Tug of War  If team A pulls with 500 N of force and team B pulls with 500 N of force, what is the total?  F T(A on rope), F T(right on left) = 500 N  F T(B on rope), F T(left on right) = 500 N  Because they are equal and opposite  Tension of rope = 500 N