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Speed | Convert from kilometer/hour to speed of light [air] |
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Common Speed Conversions Unit Definition (kilometer/hour) The kilometre per hour (American English: kilometer per hour) is a unit of both speed (scalar) and velocity (vector). The unit symbol is km/h or km·h−1; however, the colloquial abbreviations "kph" and "kmph" are sometimes also used in English-speaking countries, in analogy to mph, although these are not in accordance with international scientific standards. In North American slang and military usage, km/h (as well as km) is commonly pronounced, and sometimes even written, as klicks or kays (K's), although these may also be used to refer to kilometres.
The km/h is the worldwide most commonly used speed unit on road signs and car speedometers. Therefore, it is far more common in everyday usage than the proper SI unit of speed, m/s. Along with the kW·h, km/h is the most commonly used metric unit based on the hour, which is only a "non-SI unit accepted for use with the International System of Units" by the BIPM Unit Definition (speed of light [air]) The speed of light in a vacuum is exactly equal to 299,792,458 metres per second (approximately 186,282.4 miles per second). The speed of light is denoted by the letter c, reputedly from the Latin celeritas, "speed", and also known as Einstein's constant. This exact speed is a definition, not a measurement, as the metre itself is defined in terms of the speed of light and the second.
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