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# Speed

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**Speed** is the distance that an object moves in a certain amount of time. Speed is a measure of how fast something is moving. The **average speed** of an object in a certain time is the distance the object traveled divided by the time. Speed is a scalar.

## Contents

## Finding speed

To find speed [math]s[/math],

[math]s =[/math][math] d \over t[/math]

where [math]d[/math] is the distance and [math]t[/math] is the time that has gone by.

## Units of measurement for speed

There are many units of measurement for speed. For example, an object's speed can be measured in

- miles per hour (mph),
- kilometers per hour (km/h)
- meters per second (m/s), which is the SI-unit for speed.

## Changing speed

When an object changes speed, it gets faster or slower. If the speed of the object increases, it is called acceleration. If the object gets slower, and the speed decreases, it is called deceleration, or negative acceleration.