Speed
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Abstract from DBPedia 
速度（そくど、英: velocity）は、単位時間当たりの物体の位置の変化量である（位置の時間微分）。 (Source: http://dbpedia.org/resource/Speed) In everyday use and in kinematics, the speed (commonly referred to as v) of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero. Speed is as velocity. Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph). For air and marine travel, the knot is commonly used. The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c = 299792458 metres per second (approximately 1079000000 km/h or 671000000 mph). Matter cannot quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed.物理学の運動学における速さ（はやさ、英: speed）は、速度ベクトルの大きさを指す用語である。各時刻の位置が特定できるような何らかの'もの'があって、その'もの'が時間とともに移動していく場合に、その（道のりとしての）移動距離が時間的に増していく変化のすばやさ（変化率）を表す量である。速度が一定の場合は、単位時間あたりの移動距離である。 (Source: http://dbpedia.org/resource/Speed) 