A SYSTEM OF MEASUREMENT is a collection of units of measurement and
rules relating them to each other. Systems of measurement have
historically been important, regulated and defined for the purposes of
science and commerce . Systems of measurement in modern use include
the metric system , the imperial system , and
CONTENTS * 1 History * 1.1 Current practice * 2
* 5 Non-standard units * 5.1 Area
* 5.2
* 6 Units of currency * 7 Historical systems of measurement * 7.1 Africa * 7.2 Asia * 7.3 Europe * 7.4 North America * 7.5 Oceania * 7.6 South America * 8 See also * 8.1 Conversion tables * 9 Notes and references * 10 Bibliography * 11 External links HISTORY Main article:
The
Later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. (However, electrical units are not necessary for such a set. Gaussian units , for example, have only length, mass, and time as base quantities, and the ampere is defined in terms of other units.) Other quantities, such as power and speed , are derived from the base set: for example, speed is distance per unit time. Historically a wide range of units was used for the same type of quantity: in different contexts, length was measured in inches , feet , yards , fathoms , rods , chains , furlongs , miles , nautical miles , stadia , leagues , with conversion factors which were not powers of ten. Such arrangements were satisfactory in their own contexts. The preference for a more universal and consistent system (based on more rational base units) only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained from using a more rational system. However pressure built up, including from scientists and engineers for conversion to a more rational, and also internationally consistent, basis of measurement. In antiquity, _systems of measurement_ were defined locally: the different units might be defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm, or maybe the weight of water in a keg of specific size, perhaps itself defined in _hands_ and _knuckles_. The unifying characteristic is that there was some definition based on some standard. Eventually _cubits _ and _strides _ gave way to "customary units" to met the needs of merchants and scientists. In the metric system and other recent systems, a single basic unit is used for each base quantity. Often secondary units (multiples and submultiples) are derived from the basic units by multiplying by powers of ten, i.e. by simply moving the decimal point . Thus the basic metric unit of length is the metre ; a distance of 1.234 m is 1,234 millimetres, or 0.001234 kilometres. CURRENT PRACTICE Main article:
A number of other jurisdictions have laws mandating or permitting other systems of measurement in some or all contexts, such as the United Kingdom – whose road signage legislation , for instance, only allows distance signs displaying imperial units (miles or yards) – or Hong Kong. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a commonly used unit for volume, especially on bottles of beverages, and milligrams, rather than grains, are used for medications. Some other standard non-SI units are still in international use, such as nautical miles and knots in aviation and shipping. METRIC SYSTEM Main articles:
Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795. During this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries. Multiples and submultiples of metric units are related by powers of ten and their names are formed with prefixes . This relationship is compatible with the decimal system of numbers and it contributes greatly to the convenience of metric units. In the early metric system there were two base units, the metre for length and the gram for mass. The other units of length and mass, and all units of area, volume, and derived units such as density were derived from these two base units.
A number of variations on the metric system have been in use. These include gravitational systems , the centimetre–gram–second systems (cgs) useful in science, the metre–tonne–second system (mts) once used in the USSR and the metre–kilogram–second system (mks). The current international standard metric system is the International
The SI includes two classes of units which are defined and agreed internationally. The first of these classes includes the seven SI base units for length, mass, time, temperature, electric current, luminous intensity and amount of substance. The second class consists of the SI derived units . These derived units are defined in terms of the seven base units. All other quantities (e.g. work, force, power) are expressed in terms of SI derived units. IMPERIAL AND US CUSTOMARY UNITS Main articles:
Both imperial units and
While imperial and US customary systems are closely related, there
are a number of differences between them . Units of length and area
(the inch , foot , yard , mile etc.) are identical except for
surveying purposes. The
Where these systems most notably differ is in their units of volume. A US fluid ounce (fl oz), about 29.6 millilitres (ml), is slightly larger than the imperial fluid ounce (about 28.4 ml). However, as there are 16 US fl oz to a US pint and 20 imp fl oz per imperial pint, the imperial pint is about 20% larger. The same is true of quarts , gallons , etc. Six US gallons are a little less than five imperial gallons. The
NATURAL UNITS
Some other examples are as follows: * Geometric unit systems are useful in relativistic physics . In
these systems the base physical units are chosen so that the speed of
light and the gravitational constant are set equal to unity.
*
NON-STANDARD UNITS Non-standard measurement units , sometimes found in books, newspapers etc., include: AREA * The American football field , which has a playing area 100 yards (91.4 m) long by 160 feet (48.8 m) wide. This is often used by the American public media for the sizes of large buildings or parks. It is used both as a unit of length (100 yd or 91.4 m, the length of the playing field excluding goal areas) and as a unit of area (57,600 sq ft or 5,350 m2), about 1.32 acres (0.53 ha ). * British media also frequently uses the football pitch for equivalent purposes, although soccer pitches are not of a fixed size, but instead can vary within defined limits (100–130 yd or 91.4–118.9 m long, and 50–100 yd or 45.7–91.4 m wide, giving an area of 5,000 to 13,000 sq yd or 4,181 to 10,870 m2). However the UEFA Champions League field must be exactly 105 by 68 m (114.83 by 74.37 yd) giving an area of 7,140 m2 (0.714 ha) or 8,539 sq yd (1.764 acres ). Example: HSS vessels are aluminium catamarans ABOUT THE SIZE OF A FOOTBALL PITCH... - Belfast Telegraph 23 June 2007 * Larger areas are sometimes expressed as a multiple of the areas of certain American states, or subdivisions of the UK etc. ENERGY * A ton of
UNITS OF CURRENCY A unit of measurement that applies to money is called a unit of account in economics and unit of measure in accounting. This is normally a currency issued by a country or a fraction thereof; for instance, the US dollar and US cent ( 1⁄100 of a dollar), or the euro and euro cent.
HISTORICAL SYSTEMS OF MEASUREMENT Main article:
Throughout history, many official systems of measurement have been used. While no longer in official use, some of these CUSTOMARY SYSTEMS are occasionally used in day-to-day life, for instance in cooking . AFRICA * Algerian * Egyptian * Ethiopian * Eritrean * Guinean * Libyan * Malagasy * Mauritian * Mozambican * Moroccan * Seychellois * Somalian * Tunisian * South African * Tanzanian ASIA See also:
* Arabic * Afgan * Cambodian * Chinese * Hebrew (Biblical and Talmudic ) * Hindu * Indonesian * Japanese * Omani * Philippine * Mesopotamian * Persian * Singaporean * Sri Lankan * Syrian * Taiwanese * Tamil * Thai * Vietnamese * Nepalese EUROPE * Belgian * Czech * Cypriot * Danish * Dutch * English * Estonian * Finnish * French (now) * French (to 1795) * German * Greek * Hungary * Icelandic * Italian * Latvian * Luxembourgian * Maltese * Norwegian * Polish * Portuguese * Roman * Romanian * Russian * Scottish * Serbian * Slovak * Spanish * Swedish * Switzerland * Tatar * Welsh NORTH AMERICA * Costa Rican * Cuban * Haitian * Honduran * Mexico * Nicaraguan * Puerto Rican OCEANIA * Australian SOUTH AMERICA * Argentine * Bolivian * Brazilian * Chilean * Colombian * Paraguayan * Peruvian * Uruguayan * Venezuelan SEE ALSO *
CONVERSION TABLES NOTES AND REFERENCES * ^ "Statutory Instrument 2002 No. 3113 The Traffic Signs Regulations and General Directions 2002". Her Majesty's Stationery Office (HMSO). 2002. Retrieved 18 March 2010. * ^ HK Weights and Measures Ordinance * ^ Financial Accounting Standards Research Initiative: The Unit of Account Issue * ^ M. Ismail Marcinkowski, _Measures and Weights in the Islamic World. An English Translation of Professor Walther Hinz's Handbook "Islamische Maße und Gewichte"_, with a foreword by Professor Bosworth, F.B.A. Kuala Lumpur, ISTAC, 2002, ISBN 983-9379-27-5 . This work is an annotated translation of a work in German by the late German orientalist Walther Hinz, published in the _Handbuch der Orientalistik_, erste Abteilung, Ergänzungsband I, Heft 1, Leiden, The Netherlands: E. J. Brill, 1970. BIBLIOGRAPHY * Tavernor, Robert (2007), _Smoot's Ear: The Measure of Humanity_, ISBN 0-300-12492-9 EXTERNAL LINKS * CLDR - Unicode |