In physics, velocity is efined as the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI (metric) system, it is measured in metres per second: (m/s) or ms-1. The scalar absolute value (magnitude) of velocity is speed. For example, "5 metres per second" is a scalar and not a vector, whereas "5 metres per second east" is a vector. The average velocity v of an object moving through a displacement during a time interval (Δt) is described by the formula: