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The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, 1⁄640 of a square mile, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. One recognised symbol for the acre is ac, but the word "acre" is also used as the symbol.
The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments. The imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. The system came into official use across the British Empire in 1826. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement but imperial units are still used in the United Kingdom, Canada and other countries formerly part of the British Empire. The imperial system developed from what were first known as English units, as did the related system of United States customary units.
United States customary units are a system of measurements commonly used in the United States since it was formalized in 1832. The United States customary system developed from English units which were in use in the British Empire before the U.S. became an independent country. However, the United Kingdom's system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.
The pascal is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as one newton per square metre. The unit of measurement called standard atmosphere (atm) is defined as 101325 Pa.
The pound of force or pound-force is a unit of force used in some systems of measurement including English Engineering units and the foot–pound–second system. Pound-force should not be confused with foot-pound, a unit of energy, or pound-foot, a unit of torque, that may be written as "lbf⋅ft"; nor should these be confused with pound-mass, often simply called pound, which is a unit of mass.
The foot (pl. feet), abbreviation and IEEE standard symbol: ft, is a unit of length in the imperial and US customary systems of measurement. The prime symbol, ′, is a customarily used alternative symbol. Since the International Yard and Pound Agreement of 1959, one foot is defined as 0.3048 meters exactly. In customary and imperial units, one foot comprises 12 inches and one yard comprises three feet.
The foot-pound force is a unit of work or energy in the engineering and gravitational systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule.
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 U.S. customary units in the United States and metric units elsewhere. 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.
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 use include the International System of Units (SI), the modern form of the metric system, the imperial system, and United States customary units.
The link, sometimes called a Gunter’s link, is a unit of length formerly used in many English-speaking countries. In US customary units modern definition, the link is exactly 66⁄100 of a US survey foot, or exactly 7.92 inches or approximately 20.12 cm.
The spread of metrication around the world in the last two centuries has been met with both support and opposition.
Both the imperial and United States customary systems of measurement derive from earlier English systems used in the Middle Ages, that were the result of a combination of the local Anglo-Saxon units inherited from German tribes and Roman units brought by William the Conqueror after the Norman Conquest of England in 1066.
Height above mean sea level is a measure of the vertical distance of a location in reference to a historic mean sea level taken as a vertical datum. The combination of unit of measurement and the physical quantity (height) is called metres above mean sea level in the metric system, while in United States customary and imperial units it would be called feet above mean sea level.
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can be expressed as a multiple of the unit of measurement. For example, a length is a physical quantity. The metre is a unit of length that represents a definite predetermined length. When we say 10 metres, we actually mean 10 times the definite predetermined length called "metre". Measurement is a process of determining how large or small a physical quantity is as compared to a basic reference quantity of the same kind.
Some fields of engineering in the United States use a system of measurement of physical quantities known as the English Engineering Units. Despite its name, the system is based on United States customary units of measure.
In Nepal, some customary units of measurement are still used, although the metric system has been the official standard since 1968.
The Imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.
Several units of measurements are used in Puerto Rico. The metric system has been compulsory since 1860 in Puerto Rico. One notable exception are public roadway speed limits: whereas distances are shown in the metric system (kilometers), speed limits are posted in the United States customary units.
References
- ↑ "Pau". sizes.com. 8 March 2008.
- ↑ Gyllenbok, Jan (2018-04-12). Encyclopaedia of Historical Metrology, Weights, and Measures. Birkhäuser. ISBN 9783319667126.
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