speed
Average speed is calculated by dividing the total distance travelled by the time interval. For example, someone who takes 40 minutes to drive 20 miles north and then 20 miles south to end up at the same place , has an average speed of 40 miles divided by 40 minutes, or 1 mile per minute 60 mph . Average velocity, however, involves total displacement, instead of distance. It is calculated by dividing the total displacement by the time interval. In this example, the driver's displacement is zero, which makes the average velocity zero mph.