Metre
This pageaboutmetre asunitmeasurement. For other uses see Metre (disambiguation)
The metre (symbol: m, spelled meterAmerican English) isSI base unitlength. Itdefined aslengthpath traveled by lightvacuum duringtime interval1/299,792,458 ofsecond. See 1 E0 mcomparisons oflength ofmetre.
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Multiples
SI prefixesusedname multiplessubdivisions ofmetre. The most commonly used ones are:
- kilometre = 1,000 metres
- decametre = 10 metres (rare)
- centimetre = 1/100 metre
- millimetre = 1/1000 metre
- micrometre (formerly micron) = 1 millionth ofmetre
- nanometre = 1 billionth ofmetre
- picometre = 10-12 ofmetre
- femtometre = 10-15 ofmetre
History
The metre was originally defined1791 byFrench AcademySciences as 1/10,000,000 ofdistance alongEarth's surface fromNorth Pole toEquator alongmeridianParison April 7, 1795 France adoptedmetre as its official unitlength. Uncertainty inmeasurementthat distance ledInternational BureauWeightsMeasures1889redefinemetre asdistance between two lines onstandard barplatinum-iridium kept at Sevres.
In 1960, as lasers had become available,11th General Conference on WeightsMeasures changeddefinitionmetrebelength1,650,763.73 wavelengthsvacuum oforange-red emission line inspectrumkrypton-86. In 1983General Conference on WeightsMeasures definedmetre asdistance traveled by light invacuum1/299,792,458 ofsecond (that is,speedlight invacuum was definedbe 299,792,458 metres per second). Sincespeedlightvacuumbelievedbesame everywhere, this definitioneasiermaintainmore consistent thanmeasurement based oncircumference ofEarth orlength ofspecific metal bar. Thus, shouldbar be destroyed or lost,standard meter can still be easily recreatedany laboratory. It also hasadvantage thatcan (at leasttheory) be measuredfar greater precision thancircumference ofearth ordistance between two lines.
See also: SI, conversionunits
