Here's why:

* Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* Acceleration is the rate of change of velocity. This change can be in magnitude (speeding up or slowing down) or direction (changing direction).

In simpler terms:

* If you're driving a car and you press the gas pedal, you increase your speed (magnitude of velocity). This is acceleration.

* If you turn the steering wheel, you change your direction (even if you maintain the same speed). This is also acceleration.

Important Note: Acceleration is a vector quantity too. Its direction is the same as the change in velocity.