Here's why:

* Velocity is a measure of how fast an object is moving and in what direction. It's a vector quantity.

* Acceleration describes how the velocity of an object changes over time. It's also a vector quantity, meaning it has both magnitude (how much the velocity changes) and direction (whether the velocity is increasing, decreasing, or changing direction).

In simpler terms:

* If you're driving a car and you speed up, you're accelerating.

* If you're driving and you slow down, you're also accelerating (but in the opposite direction).

* If you're driving at a constant speed and turn a corner, you're accelerating because your direction is changing.

The formula for acceleration is:

* a = (v_f - v_i) / t

Where:

* a is acceleration

* v_f is final velocity

* v_i is initial velocity

* t is time