Which of the following is not an example of $acceleration$?

• A. A ball slowing down as it rolls to a stop
• B. A car moving at a constant $speed$ in a straight line
• C. An elevator speeding up as it begins to ascend
• D. A runner changing direction while maintaining $speed$

Answer: (B)

Verified step by step guidance

1. Recall the definition of acceleration: acceleration is the rate of change of velocity with respect to time. Velocity includes both speed and direction, so acceleration occurs if either speed or direction changes.
2. Analyze each option to determine if there is a change in velocity (speed or direction):
3. Option 1: A ball slowing down as it rolls to a stop — the speed decreases, so there is acceleration.
4. Option 2: A car moving at a constant speed in a straight line — speed is constant and direction is constant, so velocity does not change, meaning no acceleration.
5. Option 3: An elevator speeding up as it begins to ascend — speed increases, so there is acceleration; Option 4: A runner changing direction while maintaining speed — direction changes, so velocity changes, meaning there is acceleration.