Here's why:

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

* Acceleration is the rate of change of velocity over time. This means that acceleration occurs when:

* Speed changes: The object is speeding up or slowing down.

* Direction changes: The object is changing its direction of motion, even if its speed remains constant.

So, whether an object is speeding up, slowing down, or changing direction, it is undergoing acceleration.