Contact and non-contact forces

Contact forces

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

Non-contact forces

Non-contact forces are forces that act between two objects that are not physically touching each other.

When the wind pushes against an umbrella, it can change the shape of the umbrella and/or the speed of the umbrella.

Three people walking through snow and strong winds.

What happens depends on which direction the wind is blowing and how strongly it is blowing.

A measurement that needs both a size and a direction to describe it is called a vector. Vector quantities have both magnitude and an associated direction.

Some examples of vector quantities include:

  • force - 20 newtons (N) to the left
  • velocity - 11 metres per second (m/s) upwards
  • acceleration - 9.8 metres per second squared (m/s²) downwards

The direction of a vector can be given in a written description, or drawn as an arrow. The length of an arrow represents the magnitude of the quantity. The diagrams show three examples of vectors, drawn to different scales.

Examples of vectors

A measurement that doesn't have a direction is called a scalar. Scalar quantities only have a magnitude or size.

Some examples of scalar quantities include:

  • temperature - 10 degrees Celsius (°C)
  • mass - 5 kilograms (kg)
  • energy - 2,000 joules (J)