Speed and Velocity

For average speed, add all distances and divide by total time. For average velocity, find displacement from start to finish and divide by total time with direction.

A circular track or back-and-forth line diagram can show non-zero distance with zero displacement.

Writing average velocity as 5 m/s in the worked example is wrong because that uses distance instead of displacement.

Speed is the distance travelled per unit time. Velocity is the displacement per unit time in a specified direction.

Speed is the distance travelled per unit time. Velocity is the displacement per unit time in a specified direction. Average speed = total distance / total time. Average velocity = displacement / total time. SI unit for both is metre per second, written as m/s. If a runner completes one round of a circular track and returns to the start, average speed is not zero, but average velocity is zero.

Average speed depends on total distance, while average velocity depends on total displacement. Both have SI unit m/s, but velocity can be positive, negative, or zero depending on direction and displacement. Average speed = total distance / total time. Average velocity = displacement / total time. SI unit for both is metre per second, written as m/s. A cyclist travels 100 m east in 20 s and then 100 m west in 20 s. Total distance = 200 m, time = 40 s, average speed = 5 m/s. Displacement = 0, so average velocity = 0 m/s. Questions often give a round trip, a return journey, or a direction change and ask for average speed and average velocity. Writing average velocity as 5 m/s in the worked example is wrong because that uses distance instead of displacement.