Here's why:

* Velocity is the speed and direction of an object.

* Acceleration measures how quickly an object's velocity changes. This change can be in speed, direction, or both.

Think of it this way:

* If you're driving a car and you increase your speed, you are accelerating.

* If you're driving around a corner at a constant speed, you are still accelerating because your direction is changing.

* If you slam on your brakes, you are decelerating (negative acceleration) because your speed is decreasing.