Velocity

Velocity is defined as the rate of change of displacement:

$v = \frac{\Delta s}{\Delta t}$

Velocity is a vector (magnitude and direction). Speed is the scalar equivalent (magnitude only).

An object moving at constant speed in a circle has a changing velocity because its direction is changing. This means it is accelerating, even though its speed is constant.

On a displacement-time graph, velocity equals the gradient. On a velocity-time graph, the area under the curve equals the displacement.