What is speed?
Speed tells us how fast something moves. A fast car has a high speed; a slow snail has a low speed. Speed depends on the distance travelled and the time taken.
The speed formula
We find speed by dividing distance by time:
Key idea
Speed = distance ÷ time
Units: metres per second (m/s) or kilometres per hour (km/h).
If distance is in metres and time in seconds, the speed is in m/s. If distance is in kilometres and time in hours, the speed is in km/h.
A worked example
Example
A boy cycles 100 metres in 20 seconds.
Speed = distance ÷ time = 100 ÷ 20 = 5 m/s.
So he moves 5 metres every second.
Another example: a car travels 120 km in 2 hours. Speed = 120 ÷ 2 = 60 km/h. The larger the number, the faster the object moves.