What are forces?

A force is a push or a pull.

Contact forces arise between two objects which are in contact.

Non-contact forces act between two objects which are not in contact.

Contact forces

Contact forces are forces that act between two objects which are physically touching each other.

Example: Force of friction

Two objects sliding past each other experience friction forces.

For example, a box sliding down a slope.

A box rests on an incline. There are three arrows; one acting vertically downwards from the centre of the box’s base. One arrow acts perpendicular to the incline. One arrow acts up the incline.
Friction is a force that always opposes motion. It acts in the opposite direction to the one in which the box is moving.