# Speed: Formula and units

## In a nutshell

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

## Formula for speed

The formula to calculate speed is:

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

Or, more simply:

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

## Units of speed, distance and time

#### 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 ($h$) |

## Solving speed problems

To solve problems involving speed, follow this procedure:

#### 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. |

##### Example

*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:*

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