Here's why:

* Speed tells you how fast an object is moving, but it doesn't say which way it's going.

* Direction tells you the path an object is moving along, but it doesn't say how fast it's moving.

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

For example:

* Speed: 50 mph

* Direction: North

* Velocity: 50 mph North