Knot (speed)
From Freepedia
A knot is a unit of speed, abbreviated kt or kn. It is not an SI unit. It is accepted (although discouraged) for use with the SI. It is used around the world for maritime and aviation purposes.
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Definition
1 knot = 1 nautical mile/hour = 1.852 km/h. This is the definition used in most, if not all, modern circumstances.
Conversions
1 knot is equivalent to:
- 0.51444 m/s
- 1.852 km/h
- 1.15 mi/h
Origin
In some sailing ships, speed was measured by casting the log from the stern. The log was relatively immobile, and attached by line to a reel. Some sources suggest that knots placed at a distance of 47 feet 3 inches (14.4018 m) passed through a sailor's fingers, while another used a 28 second sandglass to time the operation. The knot count would be reported and used in the sailing master's dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, or 1851.66 m/h. The difference from the accepted value today is a bit less than 0.02%.
Discussion
Because a knot is already a measure of speed, the expression "knots per hour" is a solecism. Taken literally (nautical mile/hour²), it would be a measure of acceleration.
Terms
- KTAS is "knots true airspeed", a measure of an aircraft's true airspeed through the air
- KIAS is "knots indicated airspeed", meaning the airspeed shown on the airspeed indicator
- KCAS is "knots calibrated airspeed", or indicated airspeed corrected for position error
- KEAS is "knots equivalent airspeed", which is calibrated airspeed corrected for compressibility effects.
External links
- Official SI website: Table 8. Other non-SI units currently accepted for use with the International System Their use is not encouraged.
- Conversion Calculator for Units of SPEED
