Speed is the measurement of distance travelled over a unit of time. The distance travelled is divided by the time taken to travel that distance: 30 metres travelled in 2 seconds is `frac(30)(2)` = 15 metres per second.

Because the time is dividing into the distance, the units are also shown as dividing: the units are shown as `frac(m)(s)`, or ms^-1.

For transport and other uses, the speed is shown as mph or kph, where mph is miles per hour, and kph is kilometres per hour.

The formula for speed is `text(speed) = frac(text(distance))(text(time))`, or `S = frac(D)(T)`.

Speed can vary on a journey: speed will be slower in town than on a motorway. The Average Speed is the speed between two points over a given amount of time even although the vehicle may have been going faster or slower at different parts of the journey.

Note for Higher students: Velocity has both a speed AND a direction (it is a vector).