When you know both speed and direction of a motion, you know the velocity of the object.

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 elements. It's a vector quantity, meaning it has both magnitude (speed) and direction.

For example:

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

* A car traveling at 60 mph north describes its velocity.