The rate of change in velocity is called acceleration. In the study of mechanics, acceleration is computed as it relates to time with a final unit of distance over time squared.
To compute the rate of change in velocity, or acceleration, of an object, the initial speed is subtracted from the final speed. This rate is then divided by the total length of the time period for the acceleration. For example, if a car traveled on a road for two hours and was going 30 mph at the beginning of the road and 60 mph at the end of the road, the rate of change is calculated by subtracting 30 from 60 to get a 30 mph difference. Then, the 30 miles per hour is divided by the total time of 2 hours for an acceleration result of 15 miles per hour squared.