Speed is also known as velocity, and it is calculated by dividing the distance traveled by the amount of time it took to cover that distance. This is expressed as a standard equation: V = D / T.
When calculating this equation, as with many physics formulas, it is important to note the measuring unit used to gather the data. The International System of Units, or SI, for velocity is calculated in meters per second, or m/s. Once a person calculates velocity in m/s, that velocity can be translated into nearly any unit of distance and time.
By using conversion tables, it is easy to convert m/s into miles per hour. There are 1,609.34 meters in a mile and 3,600 seconds in an hour; thus, 1609.34/3600 = 0.447m/s. Therefore, 1 mph = 0.447m/s. If a person divides the original velocity, for example 8 m/s, by 0.447 m/s, he would get an answer in mph. In this case, the answer would be 17.89 mph. This equation is also used to determine the distance traveled by an object if its velocity and the time taken are known (D = V x T), as well as time traveled if the velocity and distance are known (T = D / V).