Acceleration is any change in ______.

• A. Speed
• B. Velocity
• C. Speed or direction
• D. Direction

Answer: (C)

Acceleration is the rate at which velocity changes. Velocity includes both how fast you’re moving and the direction you’re moving in. So any change in speed or any change in direction, or both, means velocity has changed and there is acceleration. For example, speeding up on a straight road, slowing down while going straight, or turning a corner at a constant speed all involve acceleration. The best choice is the one that says speed or direction because it captures both ways velocity can change. Saying just speed misses changes in direction, and saying just direction misses changes in speed; saying velocity isn’t quite right since acceleration is the rate of change of velocity, not velocity itself.