Kilometres per hour

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kilometers per hour (American English: kilometers per hour ) is the unit of speed, which represents the number of kilometers traveled in an hour.

SI unit symbol km/h . Around the world, this is the most common unit used for speed on road signs and car speedometers.

Video Kilometres per hour

Histori

Although the meter was officially defined in 1799, the term "kilometers per hour" is not directly used - miriametre ( 10,000 meters ) and myriametre per hour is preferred over kilometers and kilometers per hour. In 1802 the term "myriamÃÆ'¨tres par heure" appeared in French literature and many French maps printed in the first half of the nineteenth century had scales in the league and myriametre, but not within kilometers. The Dutch on the other hand adopted the kilometer in 1817 but gave it a local name mijl .

Maps Kilometres per hour

History of notation

Some representations of "kilometers per hour" have been used since the term was introduced and many are still in use today; for example, a list of dictionaries "km/h", "kmph" and "km/h" as English abbreviations. The SI representations, classified as symbols, are "km/h", " km h ^-1 " and " kmÃ, Â · h ^-1 ".

Abbreviation

Abbreviations for "kilometers per hour" did not appear in English until the end of the nineteenth century.

Kilometers, long units, first appeared in English in 1810, and a combined unit of "kilometer per hour" speed was used in the US in 1866. "Kilometers per hour" did not begin to be abbreviated in prints for many years later, with several different acronyms that exist almost simultaneously.

Without central authority to dictate rules for abbreviations, various publishers have their own rules that determine whether to use uppercase, lowercase, period and so on, reflecting changes in fashion and image of publishing houses concerned. For example, news organizations such as Reuters and The Economist require "kph".

In Australia's unofficial use, km/h is sometimes pronounced and written as klicks or click .

Unit symbol

The use of symbols to replace words back to at least the late Middle Ages when Johannes Widman, writing in German in 1486, used the symbols "" and "-" to represent "additions" and "subtractions". In the early 1800s Berzelius introduced a symbolic notation to the chemical elements derived from the Latin names of the elements. Usually, "Na" is used for sodium elements (Latin: sodium ) and H ₂ O for water.

In 1879, four years after the signing of the Meter Agreement, CIPM proposed various symbols for various metric units under the auspices of CGPM. Among these are the use of the "km" symbol for "kilometers".

In 1948, as part of its preparation for SI, CGPM adopted symbols for many units of measure that did not have universally agreed symbols, one of which is the symbol "h" for "clock". At the same time, CGPM formalizes the rules for combining units - quotients can be written in one of three formats that produce "km/h" , "km h ^-1 " and " kmÃ, Â · h ^-1 " is a valid representation of" kilometers per hour ". The SI standard, which is based on MKS rather than CGS-based, was published in 1960 and has since been adopted by many authorities worldwide including academic publishers and legal authorities.

SI explicitly states that the unit symbol is not an abbreviation and must be written using a very specific set of rules. M. Danloux-Dumesnils provides the following justification for this distinction:

It has been stated that, according to Maxwell, when we write the result of measurement, the numerical value multiplies the unit. Therefore the name of the unit can be replaced with algebraic type symbols, which are shorter and easier to use in formulas. This symbol is not just an abbreviation but a symbol which, like the chemical symbol, should be used in the appropriate and determined way.

SI, and hence the use of "km/h" (or "km h ^-1 " or "kmÃ, Â · h < soup> -1 ") has now been adopted worldwide in many areas related to health and safety and in metrology. It is also the preferred measurement system in academia and education.

Alternative abbreviations in official use

• km/j or km/h (Indonesia and Malaysia)
• km/t or km/team (Norway and Sweden; also use km/h )
• kmph (Sri Lanka)
• ??./?. (Thailand also uses km/h )

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Regulatory use

During the early years of the car, each country developed its own road sign system. In 1968 the Vienna Convention on Signs and Road Signals was made under the auspices of the United Nations Economic and Social Council to harmonize road signs throughout the world. Many countries have signed conventions and adopted proposals. Speed ​​limits, signs permitted directly by the convention or have been affected by the convention are shown below:

In 1972 the EU issued an order (overhauled in 1979 to consider British and Irish interests) which required member states to leave CGS-based units supporting the SI. The use of SI implicitly requires member states to use "km/h" as an abbreviation for "kilometers per hour" on official documents.

Another EU directive, published in 1975, regulates the layout of the speedometer within the EU, and requires the text "km/h" in all languages, even if it is not a natural abbreviation for the local version of "kilometers per hour". Examples include:

• Dutch: " kilometers per uur " ("clock" is spelled uur "- does not start with" h "),
• Portuguese: "quilÃÆ'³metro por hora " ("kilometers" spelled "quilÃÆ'³metro " - does not start with "k")
• Greek: " ????????????? " (different script).

In 1988, the National Highway Traffic Safety Agency of the United States announced a rule stating that "MPH and/or km/h" should be used in a speedometer display. On May 15, 2000 it was clarified to read "MPH, or MPH and km/h". However, the Federal Vehicle Security Standard number 101 ("Control and Display") allows "medium and lowercase combinations" to represent units.

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Conversions

• 3.6 km/h? 1 m/s, SI unit speed, meters per second
• 1 km/h? 0.277 78 m/s
• 1 km/h? 0.621 37 mph? 0.911 34 feet per second
• 1 knot? 1.852 km/h (to be exact)
• 1 mile per hour? 1.609344 km/h (~ 1.61 km/h)

(The value in bold face is correct.)

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See also

• Loop
• Meters per second
• Mil hourly
• Order size (speed)
• Speed ​​limit in Canada

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Note

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References

Source of the article : Wikipedia