Idea 7of 11Builds onThe area under the lineA minus sign is a direction
Area below the line
What does area under the zero line count?
Today you'll discover
- what a line below zero means on the ground
- why that area counts against the other
- how two areas can cancel
Think firstAmara's walk: the line drops below zero
At four seconds the line drops below the zero line. Is she slowing down?
Decide first, then press Next. The shape above the dashed line is shaded, then the shape below it.
The velocity–time graph of Amara's walk: a flat piece above the dashed zero line, then a flat piece below it. After a prediction, the rectangle between the first piece and the zero line is hatched, labelled 6 metres east; then the rectangle below the zero line, labelled 6 metres west. The two together add to nothing. The last step shows a walk with 9 metres of area above and 3 below, and asks where it ends.
See the whole ideathe big idea and the key word, in one place
The big idea
Area below the line is ground covered the other way: negative.
Easy to get wrongA line below zero does not mean slowing down. It means moving the other way, and its area is ground covered the other way.
Key word
- negative area
- the area between a velocity–time line and the time axis when the line is below zero: displacement in the negative direction
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?
- Add two areas with their signs to find where a walk ends.