Speed: Formula and units

In a nutshell

Speed is a measure of how much distance is travelled within a certain amount of time.

The formula to calculate speed is:

$speed=\frac{distance}{time}$

Or, more simply:

$S=\frac{D}{T}$

measurement	units
Speed	metres per second ( $m/s$ ), kilometres per hour ( $km/h$ ), miles per hour $(mph)$
Distance	metres ( $m$ ), kilometres ( $km$ ), miles ( $miles$ )
Time	seconds ( $s$ ), hours ( $h$ )

To solve problems involving speed, follow this procedure:

1.	Identify what values you have and what variable you want to find.
2.	Rearrange the speed formula for the desired variable.
3.	Substitute in known values.
4.	Give the answer with the correct units.

A car has travelled 250 kilometres in 5 hours. What was the speed of the car?

From the given information, identify the distance and the time:

$D=250km,\,T=5$ hours

Write the speed formula (no need to rearrange as it's already given in terms of speed):

$S=\frac{D}{T}$ 

Substitute in the known values:

$S=\frac{250km}{5h}$ 

Give the answer with the correct units:

$\underline{S=50km/h}$