Speed — putting a number on motion
Speed tells you how far something travels in each unit of time.
In Grade 6 you described things as fast or slow. Now you can put a number on it.
Speed is how far something travels in a certain time. The equation is:
If you walk in , your speed is — two metres every second.
The standard unit of speed is metres per second (), although you also see kilometres per hour () on road signs.
You can rearrange the equation to find any one of the three quantities:
- to find distance: ,
- to find time: .
Most journeys are not at one steady speed — you speed up and slow down. So we often use average speed: the total distance divided by the total time. A cyclist who covers in has an average speed of , even if parts of the ride were faster or slower.
- Speed = distance ÷ time, measured in .
- Rearrange the equation to find distance or time.
- Average speed uses the total distance and total time.
- Real journeys mix faster and slower parts.