According to Newton's third law of motion, whenever two objects interact, they exert equal and opposite forces on each other.
This is often worded as 'every action has an equal and opposite reaction'. However, it is important to remember that the forces act on two different objects at the same time.
Newton's third law can be applied to examples of equilibrium situations.
When drawing force diagrams, the size of the force is represented by the length of an arrow. A longer arrow indicates a larger force. Forces are vectors. This means they have both size and direction. The direction of the arrow shows the direction in which the force is acting.
There are contact forces between the person and the pram:
There are contact forces between the box and the table:
There are non-contact gravitational forces between Earth and the satellite: