Define acceleration as the rate of change of velocity.

Acceleration is defined as the rate of change of velocity, indicating how quickly an object's velocity changes over time. It can be positive, meaning the object speeds up, or negative, indicating deceleration. This concept is crucial in understanding motion, as it relates directly to the forces acting on an object. For example, when a car accelerates, its velocity increases, demonstrating a positive acceleration. Conversely, when it slows down, it experiences negative acceleration. Understanding acceleration helps in analyzing various physical scenarios, such as vehicles in motion or objects in free fall.