Idea 3of 11Builds onHow fast, and which way
How fast the speed changes
2 m/s became 6 m/s. What changed?
Today you'll discover
- a cart whose velocity grows by the same amount every second
- how to measure how fast the velocity changes
- what 1 m/s² means in plain words
Think firstPress play: the cart speeds up
t = 0.0 s the cart: 0 m, 2 m/s [E]
How fast the speed changes: as the clock runs, the dot traces the velocity–time line and the area under it is shaded; the shaded area is the ground covered so far, printed beside it.
Watch the dot. What does it do each second?
Press play, then answer. Count how much the dot climbs from one second to the next.
A player: as the clock runs, a cart moves along a ground line faster and faster while a dot on a velocity–time graph climbs a straight line from 2 to 6 metres per second over four seconds. Then five dots, one each second, labelled 2, 3, 4, 5 and 6, with plus one printed between each pair. Then a shaded triangle under the line reading four seconds passed, changed by plus 4 metres per second, plus 1 metre per second each second. The last step shows a scooter's line and asks for its rate.
See the whole ideathe big idea and the key word, in one place
The big idea
Acceleration: how much the velocity changes each second.
Compare themVelocity says how fast the cart moves. Acceleration says how fast that is changing. A cart at a steady 6 m/s has none.
Key words
- acceleration
- the change in velocity divided by the time taken, in metres per second each second (m/s²); a vector
- velocity–time graph
- a graph with time along the bottom and velocity up the side; its slope is the acceleration and the area under it is the displacement
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?
- Work out an acceleration from two velocities and a time.