Which statement correctly contrasts average velocity and average speed?

• A. They are always equal regardless of path
• B. Average speed is not the magnitude of the average velocity unless the object has moved in a straight line
• C. Average velocity equals distance over time
• D. Average speed equals displacement over time

Answer: (B)

Average speed and average velocity come from two different ways of measuring motion. Average speed uses total distance traveled divided by total time, while average velocity uses displacement—the straight-line distance from where you started to where you ended—divided by total time.

If you move along a straight line in one direction without turning back, distance and displacement are the same, so the magnitudes of average speed and average velocity match. But for any curved or back-and-forth path, the distance traveled is greater than the straight-line displacement, so the average speed will be larger than the magnitude of the average velocity. That’s why this statement is correct: average speed is not the magnitude of the average velocity unless the motion is along a straight line.

The other ideas don’t fit because velocity uses displacement over time (not distance), and speed uses distance over time (not displacement).