Here's why:

* Velocity: Measures both speed and direction.

* Acceleration: Describes how quickly the velocity changes over time. This change could be in speed, direction, or both.

Examples:

* A car speeding up: The car's velocity increases, resulting in positive acceleration.

* A car slowing down: The car's velocity decreases, resulting in negative acceleration (also called deceleration).

* A car turning: The car's direction changes, even if its speed remains constant, resulting in acceleration because its velocity is changing.