supersonic speed: see aerodynamics.

speed, change in distance with respect to time. Speed is a scalar rather than a vector quantity; i.e., the speed of a body tells one how fast the body is moving but not the direction of the motion. If during time t a body travels over a distance s, then the average speed of that body is equal to s/t. The speed and direction of a body's motion together determine the body's velocity.

hypersonic speed: see aerodynamics.

ground speed indicator: see air navigation.

Speed, John, 1552?-1629, English historian and cartographer. He abandoned his trade as a tailor to engage in mapmaking. Many of his maps of parts of England and Wales were published in The Theatre of the Empire of Great Britain (1611). His major work, The History of Great Britain, and his Genealogies Recorded in Sacred Scripture were published c.1611; they are based largely on earlier work.

Sport of racing on ice skates. The blade of the speed skate is longer and thinner than that of the hockey or figure skate. Two types of track are used in international competition. The long track is a 400-m (about one-quarter mile) flattened oval (straight sides and curved ends) on which two skaters race simultaneously. In long track the race is against the clock rather than the opponent. The short track, a more recent development, is a 111-m (364-ft) oval on which four to six skaters race during each heat. Short track is a race to the finish line. Long-track speed skating was included in the first Winter Olympics in 1924; short-track skating was added in 1992.

Learn more about speed skating with a free trial on Britannica.com.