Speed, a scalar quantity, is the magnitude of the vector velocity:

$ v(t) = \left|\frac{d\vec r(t)}{dt}\right| $

where $ \vec r(t) $ is the three-dimensional vector displacement. The speed can be also be specified as an average speed or an instantaneous speed.

The speed is expressed in units of [distance/time], often m/s or km/h.

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