Idea 5of 11Builds onSteady change, straight lineThe whole trip, or one moment
The average sits halfway
What is the cart's average velocity?
Today you'll discover
- where the average of a steady change sits
- why the two halves balance
- a rule you can use without the graph
Think first2 m/s rising steadily to 6 m/s
Over the four seconds, what was the cart's average velocity?
Decide first, then press Next. A level line appears across the middle of the slope; read its height.
The cart's velocity–time graph: a straight line rising from 2 to 6 metres per second over four seconds. After a prediction, two small shaded triangles appear, one between the slope and a level middle line on the left and one on the right, the same size. Then the middle line's height, 4 metres per second, labelled average. The last step shows a scooter's line and asks for its average.
See the whole ideathe big idea and the key word, in one place
The big idea
Steady change: the average sits halfway between start and end.
Why it happens
The cart spent as much time below 4 m/s as above it, and by the same amounts. The two halves balance, so the average is the midline.
Key word
- halfway rule
- under uniform acceleration the average velocity is the start velocity plus the end velocity, divided by two
About this modelBelow the line means moving the other way, not slowing down.
Below the line means moving the other way, not slowing down.
Ready to use it?
- Find the average velocity of a steady speed-up.