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Miles per hour (mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour.It is used in the United Kingdom, the United States, and a number of smaller countries, most of which are UK or US territories, or have close historical ties with the UK or US.
The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).
0.51444 metres per second (approximately), 1.15078 miles per hour (approximately), 20.25372 inches per second (approximately) 1.68781 feet per second (approximately). The length of the internationally agreed nautical mile is 1 852 m. The US adopted the international definition in 1954, having previously used the US nautical mile (1 853.248 m). [6]
kilometres per hour (symbol km/h); miles per hour (symbol mi/h or mph); knots (nautical miles per hour, symbol kn or kt); feet per second (symbol fps or ft/s); Mach number (dimensionless), speed divided by the speed of sound; in natural units (dimensionless), speed divided by the speed of light in vacuum (symbol c = 299 792 458 m/s).
To help compare different orders of magnitude, the following list describes various speed levels between approximately 2.2 × 10 −18 m/s and 3.0 × 10 8 m/s (the speed of light). Values in bold are exact.
The Jiffy is the amount of time light takes to travel one femtometre (about the diameter of a nucleon). The Planck time is the time that light takes to travel one Planck length. The TU (for time unit) is a unit of time defined as 1024 μs for use in engineering. The svedberg is a time unit used for sedimentation rates (usually
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It is defined as the distance that light travels in free space in one second, and is equal to exactly 299 792 458 m (approximately 983 571 055 ft or 186 282 miles). Just as the second forms the basis for other units of time, the light-second can form the basis for other units of length, ranging from the light-nanosecond (299.8 mm or just under ...