Speed and Velocity: how fast we're going

Speed is simply how fast something is going.

In Science, we measure it in metres per second (written as m/s or ms)

We work out speed using

 Example: if I walk 6m and it takes me 3 seconds, what is my speed? Answer: speed = distance divided by time, = 6 divided by 3, = 2 metres per second

So long as you remember to show your working and get the units right, that's pretty much it for GCSE - apart from one thing: average speed.

If we think about the speed of a car during a journey from town to town, it'll vary hugely throughout the journey. Sometimes the car will be stopped at traffic lights, other times it'll be whizzing along a motorway. However, it's useful to be able to work out the average speed over the whole journey.

 Average speed is really easy to work out: total distance divided by total time for the journey.

Sometimes we're only interested in how fast something's going, other times we need to know which way it's going too. So physicists came up with the idea of velocity.

 Velocity is speed in a particular direction.

Thus we could say that a car has a speed of 10 m/s, and go on to say that it's velocity is 10 m/s northwards. if he car goes round a corner without speeding up or slowing down, then it's speed hasn't changed - but it's velocity has.