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Circular motion can occur in two possible directions. A clockwise (typically abbreviated as CW) motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite sense of rotation or revolution is (in Commonwealth English) anticlockwise (ACW), or (in North American English) counterclockwise (CCW). In a mathematical sense, a circle defined parametrically in a positive Cartesian plane by the equations and is traced counterclockwise as ''t'' increases in value. ==Origin of the term== Before clocks were commonplace, the terms "sunwise" and "deasil", "deiseil" and even "deocil" from the Scottish Gaelic language and from the same root as the Latin "dexter" ("right") were used for clockwise. "Widdershins" or "withershins" (from Middle Low German "weddersinnes", "opposite course") was used for counterclockwise. The terms clockwise and counterclockwise can only be applied to a rotational motion once a side of the rotational plane is specified, from which the rotation is observed. For example, the daily rotation of the Earth is counterclockwise when viewed from above the North Pole, and clockwise when viewed from above the South Pole. Clocks traditionally follow this sense of rotation because of the clock's predecessor: the sundial. Clocks with hands were first built in the Northern Hemisphere (see ''main article''), and they were made to work like sundials. In order for a horizontal sundial to work (in the Northern Hemisphere), it must be placed looking southward. Then, when the Sun moves in the sky (east to south to west), the shadow cast on the opposite side of the sundial moves with the same sense of rotation (west to north to east). This is why hours were drawn in sundials in that manner, and why modern clocks have their numbers set in the same way. Note, however, that on a vertical sundial (such as those placed on the walls of buildings), the shadow moves in the opposite direction, and some clocks were constructed to mimic this. The best-known surviving example is the astronomical clock in the Münster Cathedral, whose hands move counterclockwise. Occasionally, clocks whose hands revolve counterclockwise are nowadays sold as a novelty. Historically, some Jewish clocks were built that way, for example in some synagogue towers in Europe. This was done in accordance with the right-to-left reading direction of the Hebrew language. Bolivia, under the presidency of Evo Morales, shifted in 2014 to counterclockwise the clock that adorns the Plurinational Legislative Assembly in Plaza Murillo, La Paz to promote indigenous values. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「clockwise」の詳細全文を読む スポンサード リンク
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