Unit of length

Source: Wikipedia, the free encyclopedia.

A ruler, depicting two customary units of length, the centimeter and the inch

A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the

U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.[1][2][3]

Metric system

Main article: Metric system

SI

Main article: International System of Units
See also: Orders of magnitude (length)

The

kilometer
is 1000 m.

Non-SI

In the

centimeter
, or 1⁄100 of a meter. Other non-SI units are derived from decimal multiples of the meter.

Name Symbol SI value
fermi fm
femtometer
ångström
 Å 100
picometers
micron μm 1 micrometer
myriameter
 10,000 meters
x unit xu 0.1 picometer

Imperial/U.S.

Main articles: Imperial units, United States customary units, and English units § length

The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959.[2][5]

Common imperial units and U.S. customary units of length include:[6]

  • thou
    or mil (1⁄1000 of an inch)
  • inch (25.4 mm)
  • foot (12 inches, 0.3048 m)
  • yard (3 feet, 0.9144 m)
  • (terrestrial) mile (5280 feet, 1609.344 m)
  • (land) league 3 miles (4,800 m)

Marine

In addition, the following are used by sailors:

  • fathom (for depth; only in non-metric countries) (2 yards = 1.8288 m)
  • nautical mile (one minute of arc of latitude = 1852 m)

Aviation

Aviators use feet for altitude worldwide (except in Russia and China) and nautical miles for distance.[citation needed
]

Surveying

Determination of the rod, using the length of the left foot of 16 randomly chosen people coming from church service

Surveyors in the United States continue to use:

  • chain (22 yards, or 20.1168 m)
  • rod (also called pole or perch) (quarter of a chain, 51⁄2 yards, or 5.0292 m)

Building trades

The Australian building trades adopted the

plans. For example, the length two and a half meters is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm.[7][8]

Surveyor's trade

American surveyors use a decimal-based system of measurement devised by Edmund Gunter in 1620. The base unit is Gunter's chain of 66 feet (20 m) which is subdivided into 4 rods, each of 16.5 ft or 100 links of 0.66 feet. A link is abbreviated "lk", and links "lks", in old deeds and land surveys done for the government.

Science

Astronomy

Main article: Astronomical system of units

Astronomical measure uses:

Physics

In atomic physics, sub-atomic physics, and cosmology, the preferred unit of length is often related to a chosen fundamental physical constant, or combination thereof. This is often a characteristic radius or wavelength of a particle. Some common natural units of length are included in this table:

Atomic property Symbol Length, in meters Reference
The classical electron radius re 2.817940285(31)×10−15 [13]
The Compton wavelength of the electron λC 2.426310215(18)×10−12 [13]
The reduced Compton wavelength of the electron λC 3.8615926764(18)×10−13 [14]
The Compton wavelength (or reduced Compton wavelength) of any fundamental particle λx
The
Atomic unit
of length) 		a0 5.291772083(19)×10−11 [13]
The reduced wavelength of hydrogen radiation 1 / R∞ 9.112670505509(83)×10−8 [13]
The
Planck length
 𝓁P 1.616199(97)×10−35 [15]
Stoney unit of length lS 1.381×10−35
Quantum chromodynamics (QCD) unit of length lQCD 2.103×10−16
Natural units based on the electronvolt 1 eV−1 1.97×10−7

Archaic

See also: English units of length

Archaic units of distance include:

Informal

See also: List of humorous units of measurement and List of unusual units of measurement

In everyday conversation, and in informal literature, it is common to see lengths measured in units of objects of which everyone knows the approximate width. Common examples are:

Other

Horse racing and other equestrian activities keep alive:

See also

References

  1. ISBN 9781852336820
    .
  2. ^
    ISBN 9781885073723
    .
  3. ^ Judson, Lewis Van Hagen (1960). Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents, Issue,233. U.S. Department of Commerce, National Bureau of Standards. pp. 3–4. Retrieved 16 October 2012.
  4. ^ "17th General Conference on Weights and Measures (1983), Resolution 1". Retrieved 2012-09-19.
  5. ISBN 978-0198605225
    . Retrieved 8 January 2012.
  6. ^ Cardarelli 2003, pp. 29–30
  7. OCLC 27702954
    .
  8. ^ "Metrication in Australia" (PDF).
  9. S2CID 195290884
    .
  10. JSTOR 10.1086/596748
    .
  11. ^ Geoff Brumfiel (14 Sep 2012). "The astronomical unit gets fixed: Earth–Sun distance changes from slippery equation to single number". Retrieved 14 Sep 2012.
  12. ^ The IAU and astronomical units, International Astronomical Union, retrieved 2008-07-05
  13. ^
    ISBN 9781586031671
    .
  14. ^ "Compton wavelength over 2 pi". The NIST Reference on Constants, Units, and Uncertainty. NIST. Retrieved 15 October 2012.
  15. NIST
    . Retrieved 15 October 2012.

Further reading

  • Whitelaw, Ian (2007). A Measure of All Things: The Story of Man and Measurement. Macmillan.
    ISBN 9780312370268
    .
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