Knot ( unit ) - wikipedia Knot ( unit ) The knot ( / nɒt / ) is a unit of speed equal to one nautical mile per hour, exactly 1.852 km / h ( approximately 1.15078 mph ). The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers ( IEEE ) ; kt is also common. The knot is a non-SI unit that is `` accepted for use with the SI ''. Worldwide, the knot is used in meteorology, and in maritime and air navigation -- for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour. Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time. Contents 1 Definitions 2 Usage 3 Origin 4 Modern use 4.1 Aeronautical terms 5 See also 6 References 7 Further reading Definitions 1 international knot = 1 nautical mile per hour ( by definition ), 1.852 kilometres per hour ( exactly ), 0.51444 metres per second ( approximately ), 1.15078 miles per hour ( approximately ), 20.25372 inches per second ( approximately ) 1.68781 feet per second ( approximately ). 7003185200000000000 ♠ 1852 m is the length of the internationally agreed nautical mile. The US adopted the international definition in 1954, having previously used the US nautical mile ( 7003185324800000000 ♠ 1853. 248 m ). The UK adopted the international nautical mile definition in 1970, having previously used the UK Admiralty nautical mile ( 7003185318400000000 ♠ 6080 ft or 7003185318400000000 ♠ 1853. 184 m ). Conversions between common units of speed m / s km / h mph knot ft / s 1 m / s = 3.6 7000223693600000000 ♠ 2.236 936 7000194384400000000 ♠ 1.943 844 7000328084000000000 ♠ 3.280 840 1 km / h = 6999277778000000000 ♠ 0.277 778 6999621371000000000 ♠ 0.621 371 6999539957000000000 ♠ 0.539 957 6999911344000000000 ♠ 0.911 344 1 mph = 6999447040000000000 ♠ 0.447 04 7000160934400000000 ♠ 1.609 344 6999868976000000000 ♠ 0.868 976 7000146666700000000 ♠ 1.466 667 1 knot = 6999514444000000000 ♠ 0.514 444 1.852 7000115077900000000 ♠ 1.150 779 7000168781000000000 ♠ 1.687 810 1 ft / s = 6999304800000000000 ♠ 0.3048 7000109728000000000 ♠ 1.097 28 6999681818000000000 ♠ 0.681 818 6999592484000000000 ♠ 0.592 484 ( Values in bold face are exact. ) Usage The speeds of vessels relative to the fluids in which they travel ( boat speeds and air speeds ) are measured in knots. For consistency, the speeds of navigational fluids ( tidal streams, river currents and wind speeds ) are also measured in knots. Thus, speed over the ground ( SOG ) ( ground speed ( GS ) in aircraft ) and rate of progress towards a distant point ( `` velocity made good '', VMG ) are also given in knots. Origin Until the mid-19th century, vessel speed at sea was measured using a chip log. This consisted of a wooden panel, attached by line to a reel, and weighted on one edge to float perpendicularly to the water surface and thus present substantial resistance to the water moving around it. The chip log was cast over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 47 feet 3 inches ( 14.4018 m ) from each other, passed through a sailor 's fingers, while another sailor used a 30 - second sand - glass ( 28 - second sand - glass is the currently accepted timing ) 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 1.85166 km / h. The difference from the modern definition is less than 0.02 %. Derivation of knots spacing : 1 kn = 1852 m / h = 0.5144 m / s ( displaystyle 1 ( \textrm ( kn ) ) = 1852 ( \textrm ( m / h ) ) = 0.5144 ( \textrm ( m / s ) ) ), so in 28 ( displaystyle 28 ) seconds that is 14.40 ( displaystyle 14.40 ) meters per knot. Modern use Graphic scale from a Mercator projection world map, showing the change with latitude Although the unit knot does not fit within the SI system, its retention for nautical and aviation use is important because the length of a Nautical Mile, upon which the knot is based, is closely related to the size of the Earth. As a result, nautical miles and knots are convenient units to use when navigating an aircraft or ship. Standard nautical charts are on the Mercator projection and the horizontal ( East - West ) scale varies with latitude. On a chart of the North Atlantic, the scale varies by a factor of two from Florida to Greenland. A single graphic scale, of the sort on many maps, would therefore be useless on such a chart. Since the length of a nautical mile, for practical purposes, is equivalent to about a minute of latitude, a distance in nautical miles on a chart can easily be measured by using dividers and the latitude scales on the sides of the chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier. Speed is sometimes incorrectly expressed as `` knots per hour '', which is in fact a measure of acceleration. Aeronautical terms Prior to 1969, airworthiness standards for civil aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles, and speeds in miles per hour. In 1969, these standards were progressively amended to specify that distances were to be in nautical miles, and speeds in knots. The following abbreviations are used to distinguish between various measurements of airspeed : KTAS is `` knots true airspeed '', the airspeed of an aircraft relative to undisturbed air KIAS is `` knots indicated airspeed '', the speed shown on an aircraft 's pitot - static airspeed indicator KCAS is `` knots calibrated airspeed '', the indicated airspeed corrected for position error and instrument error KEAS is `` knots equivalent airspeed '', the calibrated airspeed corrected for adiabatic compressible flow for the particular altitude The indicated airspeed is close to the true airspeed only at sea level in standard conditions and at low speeds. At 11 000 m ( 36 000 ft ), an indicated airspeed of 300 kn may correspond to a true airspeed of 500 kn in standard conditions. See also Nautical portal Beaufort scale Hull speed, which deals with theoretical estimates of practical maximum speed of displacement hulls Knot count Knotted cord Metre per second Orders of magnitude ( speed ) Rope ( unit ) References Jump up ^ Bartlett, Tim ( July 2008 ) ( 2003 ). RYA Navigation Handbook. Southampton : Royal Yachting Association. Jump up ^ `` ISO 80000 - 3 : 2006 ''. International Organization for Standardization. Retrieved 20 July 2013. ^ Jump up to : `` Non-SI units accepted for use with the SI, and units based on fundamental constants ''. SI brochure ( 8th ed. ). International Bureau of Weights and Measures. The knot is defined as one nautical mile per hour. There is no internationally agreed symbol, but the symbol kn is commonly used. Jump up ^ Louis E. Barbow and Lewie V. Judson ( 1976 ). `` Appendix 4 The international nautical mile '' ( PDF ). Weights and Measures Standards of the United States, A brief history. NIST Physics Laboratory. Archived from the original ( PDF ) on 2007 - 09 - 26. Retrieved 2007 - 08 - 02. Jump up ^ Jacob Abbott ( 1858 ). Rollo on the Atlantic. DeWolfe, Fiske, & Co., Publishers. Retrieved 30 November 2011. Jump up ^ Oxford Companion to Ships and the Sea. p. 454. Jump up ^ e.g. BA Chart 73, Puerto de Huelva and Approaches, 2002 Jump up ^ Wilson, Alastair ( 22 July 2009 ). `` ' Knots an hour ' ''. The Kipling Society. Retrieved 1 December 2012. Since the 1890s or thereabouts, it has been drummed into the young seaman that a knot is a unit of speed, namely, one nautical mile per hour ; and that consequently only the uneducated speak of `` knots per hour '' or `` knots an hour ''. It was therefore inevitable that Kipling 's frequent use of this expression should grieve a number of seafaring readers, as the pages of the Kipling Journal testify. Jump up ^ For example, Part 23 of the Federal Aviation Regulations, amendment 23 -- 7, 14 September 1969 Jump up ^ `` Abbreviations and symbols ''. edocket.access.gpo.gov. Further reading Kemp, Peter ( editor ). The Oxford Companion to Ships and the Sea. Oxford university Press, 1976. ISBN 0 - 19 - 282084 - 2 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Knot_(unit)&oldid=837121502 '' Categories : Navigation Units of velocity Water transport Hidden categories : Use dmy dates from June 2017 Talk Navigation Contents About Wikipedia Afrikaans অসমীয়া Asturianu Azərbaycanca Беларуская Беларуская ( тарашкевіца ) ‎ Български Boarisch བོད ་ ཡིག Brezhoneg Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Íslenska Italiano עברית ქართული Қазақша Latviešu Lëtzebuergesch Lietuvių Македонски मराठी Nederlands 日本 語 Nordfriisk Norsk Norsk nynorsk Occitan ភាសា ខ្មែរ Piemontèis Polski Português Română Русский Scots Sicilianu Simple English سنڌي Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska ไทย Türkçe Українська Tiếng Việt Winaray 粵語 中文 59 more Edit links This page was last edited on 18 April 2018, at 21 : 06. 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Question: where does the nautical term knots come from
Answer: counting the number of knots in the line that unspooled from the reel of a chip log in a specific time