* Speed is a scalar quantity, meaning it only describes how fast something is moving.
* Velocity is a vector quantity, meaning it describes both how fast something is moving *and* in what direction.
Example:
* A car traveling at 60 mph in a straight line has constant speed and constant velocity.
* A car traveling at 60 mph around a circular track has constant speed, but its velocity is constantly changing because its direction is changing.
In summary:
* Constant speed means the magnitude of the velocity is constant.
* Constant velocity means both the magnitude and direction of the velocity are constant.
