1. Every action has an equal and opposite reaction.

2. Action and Reaction Pairs Feet impact board Board impacts feet Bedouin pulls sheep Sheep pulls bedouin Fist hits neck Neck hits fist Wheels push road Road pushes wheels

3. Action and Reaction on Different Masses Consider the recoil of a rifle… Same Force

5. Same force

6. Action and Reaction on Different Masses Consider the launch of a space shuttle… The shuttle continually recoils against the expelled gas from the rockets. No atmosphere is needed for this interaction.

7. Do Action and Reaction Forces Cancel? It depends on context… If the car is the system, then the man is an external force acting against it. This action reaction does not cancel out. The external force of the road against the man accelerates the system. BUT… If the car and the man are the system, then the force pair is internal. This action reaction does cancel out.

8. Force and Friction

9. The Rickshaw Problem Pull of man on rickshawPull of rickshaw on manPush of man on ground Push of ground on manFriction b/w cart wheels and ground Acceleration is due to net force

10. The Rickshaw Problem Net force on the rickshaw? Push of ground on man - Pull of rickshaw on man Push of man on ground – friction of ground on wheels Pull of man – friction of wheels on ground Net force on the man? Net force on the ground?