What is displacement?
Whichever route the child chose, the end result is the same: they are now some distance from the starting point, in some direction.
Displacement
The straight-line change of position from one place to another, in a given direction, is called displacement.
The magnitude of the displacement is the straight-line distance between the two places.
In the example on the previous page, whether the child took P, Q or R, the displacement is the same: 160 m east.
The direction is essential
When writing a displacement, giving the magnitude alone is not enough. The direction has to be written too.
Example — a running track
A runner going from A to B on a 200 m track covers a distance of 200 m. But the straight-line distance between A and B is only 160 m.
So the displacement is written like this:
160 m, 70° west of north
Distance and displacement compared
| Distance | Displacement | |
|---|---|---|
| Depends on | The route taken | Only the start and end points |
| Has a direction? | No | Yes |
| Can it be zero? | Not if you moved | Yes — if you came back |
One more example
A child walking a winding path from A to B covers 400 m. But the magnitude of the displacement is 120 m, in the direction AB.