Speed

Speed is the rate of distance travelled. That is how much distance is being travelled in a bit of time. To be moving fast is to cover a distance in a period of time. While to be moving slowly is to cover a distance in a period of time.

Velocity is speed in a direction and so in some circumstances the words are interchangeable. We use the letter 'v' to represent both speed and velocity.

Rearrange the equation to fill in the gaps below:

so...

Distance, d	=
Velocity, v	=
Time, t	=

The SI units of length (distance) are ,() and the SI units of time are ,() so the SI units of speed are per ,( ms^-1).

If the speed changes during a period of motion then we must make sure we use the mean speed.