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 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. The speed at which a person can walk, run or cycle depends on many factors including:

- age
- terrain
- fitness
- distance travelled

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

Method of travel | Typical speed in 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. The speed of a gentle breeze is about 4 m/s. The speed of a gale can be between 20 m/s and 30 m/s.

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

This is when:

- distance travelled (s) is measured in metres (m) or kilometres (km)
- speed (v) is measured in metres per second (m/s) or kilometres per hour (km/h)
- time (t) is measured in seconds (s) or hours (h)

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 (s):**

500 + 1,500 = 2,000 m

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

50 + 75 = 125 s

**Then rearrange s = v t to find (v):**

A train travels 50 km in 15 min, and then 30 km in a further 15 min. Calculate its average speed for the whole journey in km/h.

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

50 + 30 = 80 km

**Then calculate total time taken in hours, (t):**

15 min + 15 min = 30 min = 0.5 h

**Then rearrange s = v t to find (v):**