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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.

Typical speeds

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:

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.

Learn more on displacement, distance and speed in this podcast

Listen to the full series on ����tv Sounds.

Calculations involving speed, distance and time

The average speed of a moving object can be calculated using the equation:

This is when:

• average speed (v) is measured in metres per second (m/s)
• distance travelled (s) is measured in metres (m)
• time (t) is measured in seconds (s)

Example

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:

Then calculate total time taken:

To find v:

Converting units

It is important in motion calculations to be able to easily convert between units, in particular between metres and kilometres, and seconds and hours.

1 metre is equal to 0.001 kilometres so to convert from metres to kilometres - divide by 1,000.

1 kilometre is equal to 1,000 metres so to convert from kilometres to metres - multiply by 1,000.

1 hour is equal to 3,600 seconds so to convert from hours to seconds - multiply by 3,600.

For example: