What does acceleration refer to in physics?

Acceleration in physics specifically refers to the rate of change of velocity over time. This means that whenever an object speeds up, slows down, or changes direction, it experiences acceleration. Velocity incorporates both magnitude (speed) and direction, so any alteration in either aspect signifies an acceleration.

For instance, if a car accelerates from a resting state to a higher speed, that increase in speed represents a change in velocity. Similarly, if the car navigates a curve, even though its speed might remain constant, the change in direction constitutes acceleration. Therefore, understanding acceleration is crucial as it allows us to analyze the motion of objects in a comprehensive manner.

The other options focus on concepts that do not capture the full essence of acceleration as defined in physics. Change in time does not directly relate to motion, while change in mass does not affect how an object accelerates according to Newton's second law. Change in direction is part of acceleration but does not encompass the entirety of what acceleration entails, including changes in speed.