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Newton’s Third Law of Motion

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Newton’s Third Law of Motion

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Newton’s Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object

Newton’s Third Law of Motion

For every action, there is an equal and opposite reaction

- Newton’s third law states that for every action force there has to be a reaction force that is equal in strength and opposite in direction.

Newton’s Third Law of Motion

One force is called the action force

The other force is called the reaction force

Newton’s Third Law of Motion

The action and reaction forces are equal in strength and opposite in direction

Newton’s Third Law of Motion

Forces always come in pairs

All forces come in pairs. When

you push on the ground (action), the reaction of the ground pushing back on your foot.

It does not matter which force you call

the action or the reaction. The action and reaction forces are interchangeable.

Newton’s Third Law of Motion

DISCUSSION

Does a stick of dynamite contain force?

Newton’s Third Law of Motion

DISCUSSION

No. Force is not something an object has, it is an interaction between one object an another

Newton’s Third Law of Motion

DISCUSSION

A car accelerates along a road. Strictly speaking, what is the force that moves the car?

Newton’s Third Law of Motion

DISCUSSION

The road pushes the car along! The rotating tires push back on the road (action) and at the same time the road pushes forward on the tires (reaction)

Newton’s Third Law of Motion

Discussion:

When a cannonball is shot out of a cannon, the force exerted against the cannon is the same force that drives the cannonball. Why then does the cannonball undergo more acceleration?

Newton’s Third Law of Motion

Newton’s Third Law of Motion

How does the space shuttle get into space?

Newton’s Third Law of Motion

The shuttle's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.

Newton’s Third Law of Motion

Newton’s Third Law of Motion

An astronaut can move in space by throwing an object in the direction opposite where the astronaut wants to go.

Newton’s Third Law of Motion

Newton’s Third Law of Motion

While driving down the road, a firefly strikes the windshield of a bus and SPLAT! This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?