Compound Measurement

# Compound Measurement

GCSE(F),

Compound measures all involve measuring using more than one type of measurement.

An example of a compound measure is the speed of a car, which might be given in metres per second. This speed is the number of metres travelled in one second. So a speed of 8 metres per second is 8 metres travelled for each 1 second. The units are also divided: frac(m)(s), and will be written either as m/s or as 8ms-1 (the -1 suffix shows that the seconds are a divisor).

Density is another compound measure in common use. Density is the amount of something in something else: For example, population density is the number of people in an area: for example, 46.55 people / km2 or 46.55 people km-2. In science, engineering and other areas, density may refer to a gas, liquid or solid, and is the amount of mass for a unit of volume.

## Examples

1. A car is travelling at 50 kilometres per hour. What is the speed of the car in metres per second?

Calculate frac(50 000)(3 600) = frac(500)(36) = 13.9ms-1.