# What is speed?

• Speed is a measure of how fast something or somebody is moving.

• The units of speed are linked to the units of the distance and time being used.

• A formula triangle is a quick way to calculate the speed, distance or time.

## How do we calculate speed?

If we know the distance something has moved and the time it has taken, we can calculate its speed. We can calculate each using the triangle opposite.

Speed, distance and time are called variables. This is because they are affected by each other and therefore change as another changes. When using the triangle we cover the variable that we are calculating. Variables that are next to each other are then multiplied. Variables that are under each other are divided.

For example:

D = S × T
S = D ÷ T
T = D ÷ S

### Units of speed

The unit used for speed depends on the units for distance and time. For example:

• Distance = m (metres); Time = s (seconds); Speed = m/s (metres per second)

• Distance = km (kilometres); Time = h (hours); Speed = km/h (kilometres per hour)