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Velocity Versus Speed

How fast an object moves is measured by its velocity. Velocity is calculated by dividing the distance traveled (a length) by the time it takes to traverse the distance. The units of velocity are length per time: for example, meters per second (m/s) or feet per minute (ft/min). If a person runs 5 kilometers in 1/2 hour, his or her velocity is 10 kilometers per hour (km/hr). If an airplane travels from Los Angeles, CA, to San Diego, CA, a distance of 120 miles, in 1 hour, its velocity is 120 miles per hour (mph).

When engineers work with velocities, they must know the direction of the motion as well as the numerical value. They will sometimes call the numerical value the rate or speed, and then define a direction: the box was moved at a rate of 3 ft/s to the right, or the rocket traveled upwards at a speed of 120 m/s. Velocity is composed of both a speed and a direction.

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