# Speed and Velocity

In order to understand the difference between speed and velocity, you must first understand the difference between distance and displacement.  (visit that lesson if needed)

Speed

The rate of change in distance with respect to time.   Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity.  This means it carries no direction information with it.

(the bar indicates average and the delta means change)

Velocity
The rate of change in displacement with respect to time.  Since displacement is a vector quantity, then velocity is also a vector quantity.  It has both magnitude and direction.

This formula is considered the definition formula for average velocity.
Both speed and velocity are typically measured in units of miles per hour, kilometers per hour (Km/hr), or meters per second (m/s).