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Speed (symbol: v) is the rate of motion, or equivalently the rate of change of position, expressed as distance d moved per unit of time t. Speed is a scalar quantity with dimensions Length/ Time; the equivalent vector quantity to speed is known as velocity. Speed is measured in the same physical units of measurement as velocity, but does not contain the element of direction that velocity has. Speed is thus the magnitude component of velocity.

Units of speed include:

• metre per second, (symbol m/s), the SI derived unit
• kilometres per hour, (symbol km/h)
• miles per hour, (symbol mph)
• knot ( nautical miles per hour)
• Mach, where Mach 1 is the speed of sound; Mach n is n times as fast.
• speed of light in vacuumThe article on the vacuum cleaner is located elsewhere. In physics, a vacuum is the absence of matter in a volume of space. A partial vacuum is expressed in units of pressure. The SI unit of pressure is the pascal (abbreviated to Pa in usage). It can also (symbol c) is one of the natural units

1 m/s = 3.6 km/h

1 mph = 1.609 km/h

1 knot = 1.852 km/h = 0.514 m/s

Mach 1 = 343 m/s (=speed of sound under average circumstances) = 1234.8 km/h

c = 299,792,458 m/s

Vehicles often have a speedometerA speedometer is a device for measuring and presenting to an operator the speed of a wheeled vehicle, such as an automobile. A sample point is selected, typically at the final output (the tailshaft) of the transmission, where a flexible rotating cable is to measure the speed.

The rate of change of speed with respect to time is termed accelerationIn physics, acceleration (symbol: a is defined as the rate of change (or time derivative) of velocity. It is thus a vector quantity with dimension length/ time². In SI units, this is metre/second². To accelerate an object is to change its velocity over a. Because speed has no direction, any acceleration derived from a speed will be a scalar quantity or magnitude, and will also have no direction.

1 See also

• Orders of magnitude (speed)Orders of magnitude for speed: average rate of the Moon receding from the Earth 1. 3 nm/s growth of hair 3 nm/s. walking 1-1. 5 m/s car 30 m/s (typical speed) train 40 m/s, high-speed train 90 m/s speed of sound 330 m/s low Earth orbit 7. 5 km/s Earth in

2 External link

• Conversion: speed - English and American units to metric units