How fast on average?
Average speed is total distance divided by time.
Two runners
One runner covers 160 m in 16 s. Another covers the same 160 m in 32 s.
How would you compare how fast they went?
What this lesson covers
The idea
Average speed = total distance travelled ÷ time interval; since distance travelled has no direction, average speed has only a numerical value and no direction.
Two runners
One runner covers 160 m in 16 s. Another covers the same 160 m in 32 s.
How would you compare how fast they went?
- Divide the distance by the time for each
- Add the distance and the time for each
- Use the distance, the time does not matter
Distance and time
Set the numbers asked for and read the average speed.
Distance per second
With 160 m in 16 s, each second of the run covered 10 m on average. With 100 m in 20 s, each second covered 5 m on average. Notice that the readout is just a number: nothing in it points left or right.
Average speed = total distance travelled ÷ time interval. Since distance travelled has no direction, average speed has only a numerical value and no direction.
Notes
Average speed = total distance travelled ÷ time interval. It has a numerical value only.
Check yourself
A girl runs 160 m in 16 s. What is her average speed?
Answer: 10 m s⁻¹
160 m ÷ 16 s = 10 m s⁻¹.
A cyclist travels 90 m in 15 s. What is her average speed?
Answer: 6 m s⁻¹
90 m ÷ 15 s = 6 m s⁻¹.
Average speed has…
Which is the formula for average speed?
- both a numerical value and a direction. Distance travelled has no direction, so the average speed calculated from it has none either.
- a numerical value only, with no direction — correct. Yes!
- a direction only. Average speed is a numerical value. It has no direction.
- Displacement ÷ time interval. That is the average velocity, which is found from displacement.
- Time interval ÷ total distance travelled. This is upside down. Speed is the distance covered per unit time.
- Total distance travelled ÷ time interval — correct. Yes!