Average speed
Speed is not always the same during a journey.
Slow, then fast
A bus crawls through a busy town and then speeds up on an open road. Its speed is not the same all the time.
How do we give one speed for the whole journey?
What this lesson covers
The idea
An object may move slower or faster at different times, so total distance divided by total time gives its average speed; in this chapter, 'speed' means average speed.
Slow, then fast
A bus crawls through a busy town and then speeds up on an open road. Its speed is not the same all the time.
How do we give one speed for the whole journey?
- Divide the total distance by the total time
- Take the highest speed seen
- Take the lowest speed seen
Ride the bus
Press Start the trip. Watch the speedometer change.
One speed for all
The bus went 60 km in the first 2 h and 60 km in the last hour: 120 km in 3 h. Dividing gives 40 km/h. This is the average speed.
An object may move slower or faster at different times, so total distance ÷ total time gives its average speed; in this chapter, 'speed' means average speed.
Notes
An object may move slower or faster at different times, so total distance ÷ total time gives its average speed; in this chapter, 'speed' means average speed.
Check yourself
A bus covers 150 km in 3 h. What is its average speed?
Answer: 50 km/h
150 km ÷ 3 h = 50 km/h.
A car sometimes moves slowly and sometimes fast. The speed we find by total distance divided by total time is the …
A runner covers 400 m in 100 s. What is the average speed?
Answer: 4 m/s
400 m ÷ 100 s = 4 m/s.
In this chapter, the word 'speed' means …
- highest speed. The highest speed is the fastest the car went at one moment.
- lowest speed. The lowest speed is the slowest the car went at one moment.
- average speed — correct. Yes!
- average speed — correct. Yes!
- the speed at one moment. In this chapter, speed means average speed.
- the top speed. In this chapter, speed means average speed.