Key points
A force is a push or pull that causes a change in speed, direction or shape.
Newton鈥檚 third law says that for every action there is an equal and opposite reaction.
This means that when one object pushes on another with a force, the other object pushes back on the first object with the same force.
Video: How to explain forces
Have a go
Image caption, WHAT YOU NEED: Some sticky tape, a long piece of thread, a balloon and a straw.
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Forces
Newton鈥檚 third law says that for every action there is an equal and opposite reaction.
In the case of the balloon in the video, the action is the balloon pushing the air backwards; the reaction is the air pushing the balloon forwards. It is this force that makes the balloon move.
How does Newton's Third Law apply to us?
We cannot move independently. We require a force acting upon us from elsewhere.
When we want to move, our feet try to push the ground backwards. But it is the A force which acts against the movement of an object. from the ground that pushes us forwards.
Who needs to know about forces?
Engineers designing transport need to consider forces. Something always needs to be pushed backwards if the vehicle is to move forwards.
An aeroplane鈥檚 The force which acts on a moving object to cause it to move. Thrust is often generated by an engine, for example in a car, rocket or aeroplane. depends on how much and how quickly its engines can push back the air. Boats need to consider how much and how quickly water can be forced backwards.
Quiz - Test your knowledge
Play the Atomic Labs game! game
Try out practical experiments in this KS3 science game.
More on Forces and movement
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