The movement of objects can be described using motion graphs and numerical values. These are both used to help in the design of faster and more efficient vehicles.

Distance is how far an object moves. It does not include an associated direction, so distance is a scalar quantity.

Speed is the rate of change of distance – it is the distance travelled per unit of time. Like distance, speed also does not have an associated direction, so it is a scalar quantity.

When people walk, run, or travel in a car their speed will change. They may speed up, slow down or pause for traffic.

Some typical values for speed in metres per second (m/s) include:

Method of travel | Typical speed (m/s) |
---|---|

Walking | 1.5 |

Running | 3 |

Cycling | 6 |

Car | 13 - 30 |

Train | 50 |

Aeroplane | 250 |

It is not only moving objects that have varying speed. The speed of the wind and the speed of sound also vary. A typical value for the speed of sound in air is about 330 m/s. A light breeze moves at perhaps 3 m/s, but a gale would be more than 20 m/s.

The speed of an object can be calculated using the equation:

The distance travelled by an object moving at constant speed can be calculated using the equation:

distance travelled = average speed × time taken

This is when:

- distance travelled (
*x*) is measured in metres (m) - speed (
*v*) is measured in metres per second (m/s) - time taken (
*t*) is measured in seconds (s)

A car travels 500 m in 50 s, then 1,500 m in 75 s. Calculate its average speed for the whole journey.

**First calculate total distance travelled (x):**

500 + 1,500 = 2,000 m

**Then calculate total time taken (t): **

50 + 75 = 125 s

**Then find (v): **

v = 2000 ÷ 125

v = 16 m/s

To calculate the speed of an object two measurements are needed:

- how far it travels
- the time it takes to move that distance

These measurements can be made using different types of equipment:

Equipment | Distance measurement | Time measurement |
---|---|---|

Ruler and stopwatch | Ruler measures distance travelled | Stopwatch measures time taken |

Light gates | Size of object, measured with a ruler | Light gate connects to a timer, which gives the reading |

Video analysis | Distance moved from frame to frame observed on a ruler in the pictures | The time between frames is known |