Acceleration is

• A. The speed of an object
• B. The average velocity of an object
• C. The rate at which velocity changes, and direction change
• D. The distance traveled over time

Answer: (C)

Acceleration is the rate at which velocity changes, and velocity includes both how fast something is moving and the direction it’s moving. So any change in speed or any change in direction produces acceleration. For example, speeding up or slowing down changes velocity, and moving around a curve at constant speed also changes velocity because the direction is changing, giving acceleration. If velocity doesn’t change at all, there is no acceleration.

This isn’t just about speed, which is only how fast something moves. It’s also not about average velocity (displacement over time) or distance traveled per time, which describe aspects of speed or how far something goes, not how its velocity changes.