Velocity is the time rate of change of the position of a body. Mathematically, velocity is a vector quantity having direction as well as magnitude. Speed, on the other hand, is a scalar quantity which has only magnitude. The magnitude of velocity is expressed in units such as miles per hour or meters per second when describing motion along a straight or curved path. A body which is rotating about an axis has angular velocity. Angular velocity is also a vector quantity and is expressed as units of angular rotation per unit of time such as revolutions per minute or radians per second.