**Definition:**Velocity is a vector measurement of the rate and direction of motion or, in other terms, the rate and direction of the change in the position of an object. The scalar (absolute value) magnitude of the velocity vector is the speed of the motion. In calculus terms, velocity is the first derivative of position with respect to time.

The most common way to calculate the constant velocity of an object moving in a straight line is with the formula:

r=d/twhere

ris the rate, or speed (sometimes denoted asv, for velocity, as in this kinematics article)dis the distance movedtis the time it takes to complete the movement

The SI units for velocity are m / s (meters per second).