Average speed
Now consider data for a different object.
| Time t (s) | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Distance d (m) | 0 | 3 | 5 | 9 | 12 | 16 | 18 |
Second by second
First second 3 m · second second 2 m · third second 4 m
The distance moved in each second is not the same, so the object is not travelling at a uniform speed.
So what do we do?
When an object moves with a speed that is not uniform like this, it is useful to calculate its average speed over a given time.
Average speed
average speed = total distance ÷ total time taken
Total distance in 6 s = 18 m
Average speed = 18 m ÷ 6 s = 3 m s−1
Be careful
An average speed of 3 m s−1 does not mean the object was going at 3 m s−1 at every moment. It is simply the one steady speed that would have covered the same journey.
An everyday example
Consider a vehicle that travels 100 km from a point near Colombo to Peradeniya in 2 hours.
On a journey like that, a vehicle cannot possibly hold one speed the whole way — there are stops, traffic and bends. But the average speed is still easy to work out:
100 km ÷ 2 h = 50 kilometres per hour