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. The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... ...

Definition

1 knot = 1 nautical mile/hour = 1.852 km/h. This is the definition used in most, if not all, modern circumstances. A nautical mile is a unit of length. ...

Conversions

1 knot is equivalent to:

• 0.51444 m/s
• 1.852 km/h
• 1.15 mi/h
• 1 minute of 1 degree of longitude traveled east or westbound at the equator, per hour
• 6,076 feet/hour

Origin

In some sailing ships, speed was measured by casting the chip 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%. A chip log is a navigational tool used by mariners to determine speed through the water. ... A log is a device used in navigation to measure the speed of a ship. ... Some knots: 1. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ... Hourglass An hourglass, also known as a sandglass or sand timer, is a device for the measurement of time. ... Dead reckoning is the process of estimating a global position of a vehicle by advancing a known position using course, speed, time and distance to be traveled. ... There are several traditions of navigation. ...

Discussion

Because a knot is defined as a nautical mile/hour, the expression "knots per hour" is considered incorrect as a unit of speed, since this suggests (nautical mile/hour²), which would be a measure of acceleration. Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ...

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.

True airspeed is the actual speed of an aircraft through the airmass in which it flys. ... Aircraft display an Indicated Airspeed (abbreviated IAS) on an instrument called an airspeed indicator. ... Airspeed Indicator The airspeed indicator is an instrument used in an aircraft to display the crafts airspeed, typically in knots, to the pilot. ... Calibrated airspeed (CAS) is the speed theoretically shown by a simple airspeed indicator that is free from instrument error and position error. ... Most aircraft have an inherent difference between (theoretical) calibrated airspeed (CAS) and the airspeed actually shown on the instrument (indicated airspeed, or IAS). ... Equivalent airspeed (EAS) is the airspeed which represents the same dynamic pressure at altitude that would be generated by flying at the corresponding true airspeed (TAS) at sea level. ... A compressible flow is a situation in which the compressibility of a fluid must be taken into account. ...

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