Yard

1 yard =
SI units
0.91440 m 914.40 mm
US customary / Imperial units
3.0000 ft 36.000 in
Standard lengths on the wall of the Royal Observatory, Greenwich, London - 1 yard (3 feet), 2 feet, 1 foot, 6 inches (1/2 foot), and 3 inches. The separation of the inside faces of the markers is exact at an ambient temperature of 60 °F (16 °C) and a rod of the correct measure, resting on the pins, will fit snugly between them.[1][2]
This derivation of the Vitruvian Man by Leonardo da Vinci, depicts nine historical units of measurement: the yard, the span, the cubit, the Flemish ell, the English ell, the French ell, the fathom, the hand, and the foot. The Vitruvian Man was drawn to scale, so the units depicted are displayed with their proper historical ratios.

A yard (abbreviation: yd) is a unit of length in several different systems, including English units, Imperial units, and United States customary units. It is equal to 3 feet or 36 inches, although its length in SI units varied slightly from system to system. The most commonly used yard today is the international yard, which is defined to be exactly 0.9144 metre.

Contents

Equivalence to other units of length

1 international yard is equal to:

The early yard was divided by the binary method into two, four, eight, and sixteen parts called the half-yard, span, finger, and nail. Two yards are a fathom.

Historical origin

The yard derives its name from the word for a straight branch or rod,[4] although the precise origin of the measure is not definitely known. Some believe it derived from the double cubit, or that it originated from cubic measure, others from its near equivalents, like the length of a stride or pace. One postulate was that the yard was derived from the girth of a person's waist, while another claim held that the measure was invented by Henry I of England as being the distance between the tip of his nose and the end of his thumb.[5] It was first defined in law by Edward I of England in 1305,[6][7][8] and again by Edward III of England in 1353.[9]

Following the destruction of the British Standard Yard in the 1834 fire at the Palace of Westminster, consideration was given to a reproducible standard should the physical measure be lost again. The Weights and Measures Act 1855 Act was passed defining the standard yard based upon the length of a seconds pendulum.[10] This is 39.1392 inches, and can be derived from the number of beats (86,400) between two meridians of the sun. The 36-inch yard was defined accordingly. The temperature compensated pendulum was to be held in a vacuum at sea level in Greenwich, London to give the length of the standard yard.[11] However, a new physical Imperial Standard Yard was authorised by the Weights and Measures Act 1878,[12] and was the legal standard in the United Kingdom until 1964. The "United Kingdom primary standard of the yard" (the old "Imperial Standard Yard") was measured as 0.914 396 9 metres in May 1963, one part in 300,000 shorter than the international yard that became the new legal standard, and was found to be shortening at a rate of about one part per million every 23 years.[13]

Current use

The yard is used as the standard unit of field-length measurement in American,[14]Canadian,[15]Association football,[16] and Cricket.[17]

There are corresponding units of area and volume, the square yard and cubic yard respectively, and these are sometimes referred to simply as "yards" when no ambiguity is possible. For example, an American or Canadian concrete mixer marked with a capacity of "11 yards" or "1.5 yards", where cubic yards are obviously referred to.

Yards are also used in road signs on roads in the United Kingdom[18] and the United States to specify short distances.

See also

References

  1. ↑ Bennett, Keith (2004), Bucher, Jay L., ed., The Metrology Handbook, Milwaukee, WI: American Society for Quality Measurement, p. 8, ISBN 978-0-87389-620-7 .
  2. ↑ Walford, Edward (1878), Old and New London, VI, http://www.british-history.ac.uk/report.aspx?compid=45276 .
  3. ↑ A. V. Astin & H. Arnold Karo, (1959), Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)
  4. ↑ "yard2", A New Dictionary of English on Historical Principles, 10b, Oxford: University Press, 1928, pp. 16–17 .
  5. ↑ Hone, William (1839), The Every-day Book and Table Book, London: R. Griffin & Co., p. 378, http://books.google.com/?id=IzoHAAAAQAAJ .
  6. ↑ 33 Edw. I, c. 6.
  7. ↑ Bigg, P. H.; Anderton, Pamela (1963), "The Yard Unit of Length", Nature 200: 730–32, doi:10.1038/200730a0 
  8. ↑ Watson, C. M. (1910), British Weights and Measures, London: John Murray, pp. 36–39, http://www.archive.org/details/britishweightsme00watsuoft .
  9. ↑ 27 Edw. III, c. 10.
  10. ↑ 18&19 Vic., c. 72.
  11. ↑ Bunch, Bryan H.; Hellemans, Alexander (1988), The Timetables of Science, Simon & Schuster, ISBN 0671621300, http://books.google.com/?id=qg0PAAAACAAJ .
  12. ↑ Glazebrook, Richard (1922), "Measurement, Units of", Dictionary of Applied Physics, 1, pp. 580–88, http://www.archive.org/details/dictionaryofappl025484mbp .
  13. ↑ Bigg, P. H.; Anderton, Pamela (1964), "The United Kingdom standards of the yard in terms of the metre", Br. J. Appl. Phys. 15: 291, doi:10.1088/0508-3443/15/3/308 .
  14. ↑ American Football pitch dimensions
  15. ↑ Canadian Football Pitch dimensions
  16. ↑ Association Football pitch dimensions
  17. ↑ Cricket pitch dimesions
  18. ↑ Driving Standards Agency (1999), The Highway Code, London: The Stationery Office, ISBN 0 11 551977 7, pp. 74–75