platform tennis, version of lawn tennis played on an elevated wooden or aluminum court that is one fourth the size of a standard court, usually by doubles teams. Unlike lawn tennis, platform tennis allows only one serve, and balls may be played off the 12-ft-high (3.7-m) wire-mesh screen that completely enclose the court. A perforated wooden paddle is used instead of a racquet, and the ball is smaller, solid, and made of sponge rubber. The game was devised in 1928 to provide for winter tennis, the platform being more easily cleared of snow than a regular court.

diving, springboard and platform, sport of entering the water from a raised position, often while executing tumbles, twists, and other acrobatic maneuvers. In most dives the upper part of the body enters the water first, and the arms are extended straight over the head. The earliest recorded major diving competition took place in 1871 off the London Bridge. Since then diving has become part of most aquatic meets and is a U.S. intercollegiate event. Men's diving became part of the Olympic games in 1904, when it was called fancy diving. Women's diving joined the program in 1912; synchronized diving became a medal event in 2000.

Springboard diving is done from a flexible plank made of aluminum or steel and measuring 16 ft (4.9 m) long by 20 in. (51 cm) wide. It extends horizontally over the water at a height of 1 m (about 3 ft 3 in.) or 3 m (about 9 ft 10 in.). The flexibility of the board allows the diver to jump high into the air to execute various maneuvers before entering the water. Platform diving (also called high diving) is usually done from a tower 10 m (32 ft 10 in.) high that is not flexible and that projects nearly five feet (1.5 m) over the water. The height of the tower permits more involved acrobatics during descent; it also poses considerable danger as divers enter the water at speeds of 40 mi (60 km) per hr or more.

Both types of diving are done from standing and walking starts, and in competition judges score on the basis of form, execution, and degree of difficulty. There are six groups of dives (forward, backward, reverse, inward, twisting, and armstand) and four basic midair body positions: tuck (bending at both the knees and the hips so that the body assumes a ball shape), pike (bending at the hips but not at the knees), straight (body rigidly extended at all times), and free (combination of two or more of above body positions). On springboard, divers usually perform five dives with degree-of-difficulty limits—one dive from each group except armstand—and five dives (six for men) with no limits. On platform, divers perform four dives with difficulty limits from the six groups. Women then perform four dives, men six, without limits. In all dives the final entry position should be rigid and vertical—the less splash the better.

Siberian Platform or Angara Shield, large, geologically stable area of Precambrian rocks, N Asia, comprising much of Siberia, Russia. It is bounded, in general, on the west by the Yenisei River, on the east by the Lena River, on the north by the Arctic Ocean, and on the south by the general latitude of Lake Baykal. Most of the region is covered by strata of lower Paleozoic sediments and it is thought that since the early Paleozoic era it has remained above the level of invading seas that flooded most continental land masses. Tundra and taiga cover the region, which also has a rich variety of minerals.

Saybrook Platform: see Cambridge Platform.

Russian Platform: see Baltic Shield.

Cambridge Platform, declaration of principles of church government and discipline, forming in fact a constitution of the Congregational churches. It was adopted (1648) by a church synod at Cambridge, Mass., and remains the basis of the temporal government of the churches. It had little to do with matters of doctrine and belief. The Congregationalists of Connecticut later subscribed (1708), in the Saybrook Platform, to a more centralized church government, resembling Presbyterianism. See also Congregationalism.

or abrasion platform

Gently sloping rock ledge that extends from the high-tide level at a steep cliff base to below the low-tide level. It develops as a result of wave abrasion; beaches protect the shore from abrasion and therefore prevent the formation of platforms. A platform is broadened as waves erode a notch at the base of the sea cliff, causing overhanging rock to fall. As the sea cliffs are attacked, weak rocks are quickly eroded, leaving the more resistant rocks as protrusions.

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Variation of paddle tennis, played on a platform enclosed by a wire fence. It was devised in 1928 in Scarsdale, N.Y., U.S. The short-handled oval paddles are made of perforated plywood; the balls are made of sponge rubber. The rules are the same as for tennis, except that balls may be played off back or side walls after first striking inside the court.

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