Here's why:

* Velocity is a measure of how fast an object is moving *and* in what direction.

* Acceleration is the change in velocity over a period of time. It describes how quickly the object's speed or direction is changing.

Key points about acceleration:

* Units: Acceleration is measured in units of distance per time squared, such as meters per second squared (m/s²).

* Positive and negative: Positive acceleration means the object is speeding up, while negative acceleration means it's slowing down (also known as deceleration).

* Change in direction: Even if an object's speed is constant, it can still be accelerating if its direction is changing (like an object moving in a circle).

Let me know if you'd like more information about acceleration!