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(General and Credit) In your Standard Grade Physics course you are expected to know Newton's Third Law and be able to use it in explaining how movement is produced.

You may wish to print a hard copy for your reference.

Newton's Third Law.

A simple way of stating Newton's Third Law is to say:

"If A exerts a force on B, then B in turn exerts a force on A."

For the Credit Level examination you would be expected to be more precise in your statement of the Law. For Credit Level you would say:

"If A exerts a force on B then B will exert an equal and opposite force on A"

This video shows how this law works in two real life situations involving skateboarders, and rockets.

Video: Newton's third law

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Newton's third law is saying that when you push on something, then, that something, whatever it is, pushes back on you.

Walking on grass, demonstrating Newton's Third Law. The sole of the shoe on grass creates a force pushing backwards, and while the push from grass on the sole of the shoe creates a force pushing forward.

For example, when you are walking along the grass you push backwards on the grass and the grass pushes forwards on you. These two pushing forces are the result of the friction force between the sole of your shoe and the grass . When you take a step forwards the sole of your shoe pushes backwards on the grass. By Newton's Third Law the grass pushes forwards on the sole of your shoe. It is this frictional push from the grass that enables you to move forwards. Walking would be impossible without this force of friction, between the grass and the sole of your shoe, pushing on you.

This video explains how friction works, and demonstrates how surprisingly strong a force it can be.

Video: Friction

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A picture of a boy.

Class Clips

An astronaut describes being weightless in space.

This video explains more about weight and gravity:

Weight and gravitational field strength


A picture of Mia Cadaver

Tombstone Timeout

Test out your knowledge of physics with Mia Cadaver's physics game - it's serious fun!

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