In Newtonian mechanics '''displacement''' is one of two subtly different quantities measuring distance and direction

along a path

(a)

**Displacement** in the sense of

**position vector** is a vector quantity which expresses position by the length and direction of a straight line from one

place to another (as opposed to the scalar quantity

distance which expresses only the length) The SI unit for either

distance or displacement is the metre

(b)

**Displacement** in the sense of movement is a vector quantity which expresses the

distance and direction (in a straight line) from the starting to the finishing point

The two meanings are not the same as the table shows:

| (a) | (b) |
---|

Where are you? | **displacement** | Position |
---|

Where are you relative to the starting point? | Change of **displacement** | **displacement** (= change in position) |
---|

Velocity | Rate of change of **displacement** | Rate of **displacement** |
---|

By plotting the

**displacement** (relative to the starting point) against

time on a position vs.

graph] the average

velocity or the instantaneous

velocity can be found by

taking the

slope of the graph or the

derivative of the graph respectively