Per 1 5 6 and 7Take notes on the following in your Physics Journals

11.13.2013

• HW will be handed out, due on FRIDAY• Quiz on Forces on Friday 11.15• TEST on Forces is THURSDAY 11.21

Newton’s Third Law of Motion

Copy into your journals!

For every action force there is an equal and opposite reaction force.

Force of balloon pushing on air

Force of air pushing on balloon

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Action: force of gases pushing on rocket

Reaction: force of rocket pushing on gases

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For every action force that can be identified there is a matching reaction force on a different object.

• Paddle pushes on water, water back on paddle, person on kayak, kayak on person. Water on kayak, kayak on water.

• Rider on horse, horse on rider.

Discuss the force pairs with a neighbor!

Action – Reaction force pairs do not “balance” because there are acting on two different objects.

Copy into your journals!

Detecting motion when paired forces are in action can be challenging because you will

only see the less massive object move.What if everyone in the world jumped at once?

Draw this picture!

Check your understanding.

• A man is pulling a wagon. Identify the objects and the interactions between them.

Man applies a force on the wagon; wagon applies a reaction force on the man’s arm.

Check your understanding.

• A roller skate glides at a constant speed on a frictionless surface. Identify the objects and the interactions between them.

• Surface exerts normal force on object; object’s weight is on surface.

• Earth exerts gravitational force on object; object exerts gravitational force on earth.

Check your understanding.

• A piano is pulled upward at a constant speed, by a person pulling downward, on a rope and pulley. Identify the objects and the interactions between them.

• Rope tension pulls on piano; rope tension pulls on person.

Check your understanding.• A car slows down. Identify the objects and the

interactions between them.

• Road exerts frictional force on car; car exerts frictional force on road.

• Surface exerts normal force on car; car’s weight is on surface.

• Earth exerts gravitational force on car; car exerts gravitational force on earth.

Check your understanding.

• A kitty lies motionless on the floor. Identify the objects and the interactions between them.

• Surface exerts normal force on object; object’s weight is on surface.

• Earth exerts gravitational force on cat; cat exerts gravitational force on earth.

Check your understanding.

• A fan hangs on a rod attached to the ceiling. Identify the objects and the interactions between them.

• Rod pulls on fan; fan pulls on rod.

Check your understanding.• An apple is falling from a tree without air

resistance opposing its motion. Identify the objects and the interactions between them.

• Earth exerts gravitational force on apple; apple exerts gravitational force on earth.