When you know both the speed and direction of an object in motion, you know its velocity.

Here's why:

* Speed tells you how fast an object is moving.

* Direction tells you which way the object is moving.

Velocity combines both of these pieces of information, giving you a complete picture of the object's motion.

For example:

* A car traveling at 60 mph is describing its speed.

* A car traveling at 60 mph eastbound is describing its velocity.