Explain the difference between average speed and average velocity. The displacement is the difference between the average speed and the average velocity. Average speed is measured in meters per second, whereas average velocity is measured in miles per hour. The average speed, a scalar, is greater than or equal to the magnitude of the average velocity vector over the same time interval. There is no difference between average speed and average velocity; they are completely equivalent terms. The average speed, a scalar, equals the magnitude of the average velocity vector over the same time interval.