Kilometres per hour explained

kilometre per hour
Standard:derived
Quantity:speed
Symbol:km/h
Units1:mph
Inunits1:0.621371
Units2:m/s
Inunits2:0.277778
Units3:kn
Inunits3:0.539957
Units4:ft/s
Inunits4:0.911344

The kilometre per hour (SI symbol: km/h; non-SI abbreviations: kph, km/hr) is a unit of speed, expressing the number of kilometres travelled in one hour.

History

Although the metre was formally defined in 1799, the term "kilometres per hour" did not come into immediate use – the myriametre and myriametre per hour were preferred to kilometres and kilometres per hour. In 1802 the term "myriamètres par heure" appeared in French literature.[1] The Dutch on the other hand adopted the kilometre in 1817 but gave it the local name of the mijl (Dutch mile).[2]

Notation history

The SI representations, classified as symbols, are "km/h", "" and "". Several other abbreviations of "kilometres per hour" have been used since the term was introduced and many are still in use today; for example, dictionaries list "kph",[3] [4] [5] "kmph" and "km/hr"[6] as English abbreviations. While these forms remain widely used, the International Bureau of Weights and Measures uses "km/h" in describing the definition and use of the International System of Units. The entries for "kph" and "kmph" in the Oxford Advanced Learner's Dictionary state that "the correct scientific unit is km/h and this is the generally preferred form".[7]

Abbreviations

Abbreviations for "kilometres per hour" did not appear in the English language until the late nineteenth century.

The kilometre, a unit of length, first appeared in English in 1810,[8] and the compound unit of speed "kilometers per hour" was in use in the US by 1866.[9] "Kilometres per hour" did not begin to be abbreviated in print until many years later, with several different abbreviations existing near-contemporaneously.

  • 1910: "km ph"[17]
  • 1911: "K.P.H."[18]
  • 1914: "km. hr."[19]
  • 1915: "km/hour"[20]
  • 1915: "km.-hr."
  • 1916: "km. per hour"[21]
  • 1921: "kms/hr."[22]

With no central authority to dictate the rules for abbreviations, various publishing houses and standards bodies have their own rules that dictate whether to use upper-case letters, lower-case letters, periods and so on, reflecting both changes in fashion and the image of the publishing house concerned,[28] In contrast to the "symbols" designated for use with the SI system, news organisations such as Reuters[29] and The Economist[30] require "kph".

In informal Australian usage, km/h is more commonly pronounced "kays" or "kays an hour". In military usage, "klicks" is used, though written as km/h.[31]

Unit symbols

In 1879, four years after the signing of the Treaty of the Metre, the International Committee for Weights and Measures (CIPM) proposed a range of symbols for the various metric units then under the auspices of the General Conference on Weights and Measures (CGPM). Among these were the use of the symbol "km" for "kilometre".[32]

In 1948, as part of its preparatory work for the SI, the CGPM adopted symbols for many units of measure that did not have universally agreed symbols, one of which was the symbol "h" for "hours". At the same time the CGPM formalised the rules for combining units quotients could be written in one of three formats resulting in, and being valid representations of "kilometres per hour". The SI standards, which were MKS-based rather than CGS-based, were published in 1960 and have since then have been adopted by many authorities around the globe including academic publishers and legal authorities.

The SI explicitly states that unit symbols are not abbreviations and are to be written using a very specific set of rules. M. Danloux-Dumesnils[33] provides the following justification for this distinction:

SI, and hence the use of (or or) has now been adopted around the world in many areas related to health and safety[34] and in metrology[35] in addition to the SI unit metres per second (or). SI is also the preferred system of measure in academia and in education.[36]

Non-SI abbreviations in official use

Regulatory use

During the early years of the motor car, each country developed its own system of road signs. In 1968 the Vienna Convention on Road Signs and Signals was drawn up under the auspices of the United Nations Economic and Social Council to harmonise road signs across the world. Many countries have since signed the convention and adopted its proposals. Speed limits signs that are either directly authorised by the convention or have been influenced by the convention are shown below:

In 1972 the EU published a directive[37] (overhauled in 1979 to take British and Irish interests into account) that required member states to abandon CGS-based units in favour of SI. The use of SI implicitly required that member states use "km/h" as the shorthand for "kilometres per hour" on official[38] documents.

Another EU directive, published in 1975, regulates the layout of speedometers within the European Union, and requires the text "km/h" in all languages,[39] even where that is not the natural abbreviation for the local version of "kilometres per hour". Examples include:

In 1988 the United States National Highway Traffic Safety Administration promulgated a rule stating that "MPH and/or km/h" were to be used in speedometer displays. On May 15, 2000, this was clarified to read "MPH, or MPH and km/h".[40] However, the Federal Motor Vehicle Safety Standard number 101 ("Controls and Displays") allows "any combination of upper- and lowercase letters" to represent the units.[41]

Conversions

See also

Notes and References

  1. Book: Develey, Emmanuel . Physique d'Emile: ou, Principes de la science de la nature . 1 . 1802 . Paris .
  2. Book: de Gelder, Jacob . Allereerste Gronden der Cijferkunst . 's-Gravenhage and Amsterdam . nl . 1824. 155–156 . de Gebroeders van Cleef . Introduction to Numeracy . 2 March 2011.
  3. 18 May 2022.
  4. https://www.merriam-webster.com/dictionary/kph "kph."
  5. https://www.collinsdictionary.com/dictionary/english/kph "kph."
  6. https://books.google.com/books?id=hCs6AAAAIAAJ&dq=km/hr&pg=PA126 Journal of Research of the National Bureau of Standards: Radio propagation. D, Volume 65, pp. 122–126. 1961.
  7. Web site: kph abbreviation . Oxford Advanced Learner's Dictionary.
  8. Web site: The Oxford English Dictionary . 13 July 2012.
  9. Book: Frazer, John F. . Journal of the Franklin Institute of the State of Pennsylvania for the Promotion of the Mechanic Arts . Franklin Institute . November 1866 . Philadelphia . 314 . LII . 5.
  10. Book: American meteorological journal: A monthly review of meteorology, medical climatology and geography . Meteorological Journal Company . Harrington . Mark W. . Rotch . A. Lawrence . Herdman . W. J. . May 1889 . 226 . 6 .
  11. Power consumed on electric railways . The Street Railway Journal . February 1895 . 11 . 2 . 116–117.
  12. Book: Bulletin – United States Geological Survey, Volumes 151–152 . USGS . 1898 . ix .
  13. The Stability of the Motion of a Bicycle . Whipple . F. J. W. . The Quarterly Journal of Pure and Applied Mathematics . 1899 . 30 . 342.
  14. Book: Launhardt, Wilhelm . The Theory of the Trace: Being a Discussion of the Principles of Location . Lawrence Asylum Press . Madras . 1900 .
  15. The Electric Problem of Railways . The Railway Engineer . 23 . Saunders . Lawrence . Blundstone . S. R. . 207 . July 1902 . Swinburne . J.
  16. Book: Figee, S. . Observations Made at the Royal Magnetical and Meteorological Observatory at Batavia . Government of Netherlands East India . 1903 . 24 . 196.
  17. Book: Hobart, H. M. . Electric Trains . D. Van Nostrand Company . New York . 1910 . xix.
  18. Foreign Notes on Aviation . Ball . Jack . Town & Country . August 1911 . 26 .
  19. A Review of Some European Electric Locomotive Designs . Dodd . S. T. . General Electric Review . January 1914 . 17 . 1 . 1141.
  20. Data on Mixed Motor Fuels of Interest for American Export Trade . The Automobile . October 1915 . 33 . 15 . 709.
  21. Tractive resistance tests with an electric motor truck . Engineering and Contracting . December 1916 . 46 . 25 . 560.
  22. Book: al-Jawwīyah, Maṣlaḥat al-Arṣād . Meteorological Report for the Year [1916?] ]. Ministry of Public Works, Egypt . xvii . 1921 .
  23. French Railway Begins Electrification Program . Railway Electrical Engineer . 13 . 392 . Candee . A. H. . Lynde . L. E. . Simmons Boardman . 1922.
  24. Book: Blakemore, Thos. L. . Pressure Airships . 1927 . 230 . Ronald Press.
  25. Book: Aircraft Year Book . Aerospace Industries Association of America, Manufacturers Aircraft Association, Aeronautical Chamber of Commerce of America . 1933 . 391–393 . 15.
  26. Book: Bulletin . Central Electric Railfans' Association . 1939 . cxii.
  27. Book: Thompson, Francis R. . Electric Transportation . 1940 . 165 .
  28. Book: Truss, Lynne . Eats Shoots and Leaves . Profile Books . 2003 . 188–189 . 1-86197-6127 . registration .
  29. Book: Reuters Handbook of Journalism . 278 . April 2008 . Reuters . 2012-08-06 . https://web.archive.org/web/20160518015851/http://handbook.reuters.com/extensions/docs/pdf/handbookofjournalism.pdf . 2016-05-18 . dead .
  30. Web site: The Economist Style Guide, 12th Edition .
  31. Web site: June 2012 . klick . . 9 July 2012.
  32. Book: Quinn, Terry . From Artefacts to Atoms: The BIPM and the Search for Ultimate Measurement Standards . 2012 . 978-0-19-530786-3 . 132 . Oxford . Oxford University Press.
  33. Book: The Metric System: A Critical Study of its Principles and Practice . The Athlone Press of the University of London . Danloux-Dumesnils . 1969 . 32.
  34. Web site: RLO: SI Units . 21 July 2012 . School of Nursing and Academic Division of Midwifery; University of Nottingham . 1 December 2006 . dead . https://archive.today/20121223075728/http://intralibrary.rlo-cetl.ac.uk:8080/intralibrary/open_virtual_file_path/i1405n24399t/2.html . 23 December 2012 .
  35. Web site: Information and Harmonization . . 20 July 2012.
  36. OLA Editorial Style Guide . Open Learning Agency (OLA), Government of British Columbia . 2000 . Burnaby, British Columbia . 26 July 2012.
  37. 71/354/EEC . 18 October 1971 . on the approximation of laws of Member States relating to units of measurement . 31971L0354.
  38. Until 2010, the directive covered "economic, public health, public safety or administrative purposes"; since then of the EU internal market.
  39. 75/443/EEC . 26 June 1975 . on the approximation of the laws of the Member States relating to the reverse and speedometer equipment of motor vehicles . 31975L0443.
  40. Federal Motor Vehicle Safety Standards; FMVSS 101--Technical Correction--Speedometer Display . National Highway Traffic Safety Administration . Federal Register . May 2000 . 64 . 94 . 30915–30918.
  41. Book: Federal Motor Vehicle Safety Standard (101: Controls and Displays) . National Highway Traffic Safety Administration . 237 .

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