Speed is the rate of motion expressed as distance moved per unit time. Speed is a scalar; the equivalent vector quantity is known as velocity.
Units of speed include:
- metre per second (symbol m.s^{-1}), the SI derived unit
- kilometre per hour, km.h^{-1}
- mile per hour
- knot (nautical miles per hour)
- Mach, where Mach 1 is the speed of sound; Mach n is n times as fast.
- 1 m.s^{-1} = 3.6 km.h^{-1}
- 1 mph = 1.609 km.h^{-1}
- 1 knot = 1.852 km.h^{-1} = 0.514 m.s^{-1}.
- Mach 1 = ca. 1200 km.h^{-1} = ca. 330 m.s^{-1};
Speed is also:
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