Velocity can be defined as the rate of change of displacement. Velocity may not always be constant it may vary with time. In this case, we define average velocity. If an object travels a total displacement, ∆x, in a time interval, ∆t , its average velocity, , is defined as

Since displacement is a vector, velocity is also a vector quantity. It is basically speed in a specific direction. The SI unit of velocity is meter per second (m/s), which is the same as the unit of speed.

In the previous lesson, you have learnt that distance traveled can be different from the magnitude of displacement. In the same way, speed can be different from the magnitude of velocity. For example, you run to a shop and return home in 30 minutes. If the total distance you traveled was 1.6 km, then your average speed was
3.2 km/h. Your average velocity, however, was zero because your displacement for the round trip was zero.