Editing Displacement (geometry) (section)

==Discussion==
In considering motions of objects over time, the instantaneous [[velocity]] of the object is the rate of change of the displacement as a function of time. The instantaneous [[speed]], then, is distinct from velocity, or the [[time rate]] of change of the distance travelled along a specific path. The velocity may be equivalently defined as the time rate of change of the position vector. If one considers a moving initial position, or equivalently a moving origin (e.g. an initial position or origin which is fixed to a train wagon, which in turn moves on its rail track), the velocity of P (e.g. a point representing the position of a passenger walking on the train) may be referred to as a ''[[relative velocity]]''; this is opposed to an ''[[absolute velocity]]'', which is computed with respect to a point and coordinate axes which are considered to be at rest (a [[inertial frame of reference]] such as, for instance, a point fixed on the floor of the train station and the usual vertical and horizontal directions).