# Contact and non-contact forces

## Contact forces

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

## 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.

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 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.

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)