Speed is the measurement of how far an object travels in a specific time. So, to determine the speed of an object, there are two measurements that are required:

**The distance that the object has travelled.**

**The time taken to cover this distance. **

When these measurements have been taken, then the speed can be calculated using the following equation.

__Example 1__

A car travelling on a motorway covers a distance of 200 metres in 4 seconds.

How fast is the car travelling?

**speed = distance ÷ time**

Distance = 200 metres

Time = 4 seconds

So all we need to do is substitute these numbers into our equation to solve:

Speed = 200 m ÷ 4 s = __ 50 m/s__ (metres per second)

__Example 2__

A motorbike travels a distance of 150 miles at an average speed of 60 mph.

How long does this journey take?

This time, we need to rearrange the equation to make **time** the subject:

**speed = distance ÷ time**

becomes

**time =** **distance ÷ speed**

And then we just substitute our numbers into the correct places:

Distance = 150 miles

Speed = 60 mph

**Time = 150 mph ÷ 60 miles = 2.5 hours**

We can double-check our answer with a reverse calculation:

The speed is equal to **150 ÷ 2.5 = 60 mph** (miles per hour)

Metres per second (m/s) is a commonly used unit to measure speed, but you are probably more familiar with miles per hour (mph) or kilometres per hour (km/h) when referring to the speed of cars. All of the units for speed are a distance unit divided by a time unit.

Are you ready to have a go at some questions now?