Main Page | See live article | Alphabetical index 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: slang for amphetamines an American film: see Speed (movie). This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.