AQA A Level Physics

Revision Notes

4.4.3 Newton's Third Law

Newton's Third Law

  • Newton’s Third Law states:

If body A exerts a force on body B, then body B will exert a force on body A of equal magnitude but in the opposite direction

  • This means that every force has a paired equal and opposite force
    • Newton’s Third Law force pairs must act on two different objects
    • Newton’s Third Law force pairs must also be of the same type e.g. gravitational or frictional

Worked Example

Using Newton’s third law describe why when a balloon is united, it travels in the opposite direction.

WE - Newtons third law question image, downloadable AS & A Level Physics revision notesWE - Newtons third law answer image, downloadable AS & A Level Physics revision notes

Exam Tip

You may have heard Newton’s Third Law as: ‘For every action is an equal and opposite reaction’. However, try and avoid using this definition since it is unclear on what the forces are acting on and can be misleading.

Worked example - Newton's third law pairs, downloadable AS & A Level Physics revision notes

Newton’s Third Law force pairs are only those that act on different objects

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