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Units for other physical quantities are derived from this set as needed. In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form = where is the acceleration in ft/s 2 and g c = 32.174 lb·ft/(lbf·s 2).
The table of imperial avoirdupois mass is the same as the United States table up to one pound, but above that point, the tables differ. The imperial system has a hundredweight, defined as eight stone of 14 lb each, or 112 lb ( 50.802 345 44 kg ), whereas a US hundredweight is 100 lb ( 45.359 237 kg ).
The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth.Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from equator to pole by up to half a percent) can safely be neglected.
The unit of volume, the gallon, has different values in the United States and in the United Kingdom – the US fluid gallon being about 0.83 imperial gallons and the US dry gallon being about 0.97 imperial gallons. The US fluid gallon was based on the wine gallon used in England prior to 1826.
The kayser (K) is a unit of wavenumber equal to 1 cm −1 (100 m −1). The gal (Gal) is a unit of acceleration equal to 1 cm/s 2. [3] The dyne (dyn) is a unit of force equal to 1 g⋅cm⋅s −2 (10 μN). [3] The barye (Ba) is a unit of pressure equal to 1 dyn⋅cm −2 (100 mPa). The erg (erg) is a unit of energy equal to 1 dyn⋅cm (100 nJ). [3]
The avoirdupois pound is legally defined as a measure of mass, [25] but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force". The slug is another unit of mass derived from pound-force.
The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road). The imperial system of units, imperial system or imperial units (also known as British Imperial [1] or Exchequer Standards of 1826) 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 US fluid ounce is based on the US gallon, which in turn is based on the wine gallon of 231 cubic inches that was used in the United Kingdom prior to 1824. With the adoption of the international inch, the US fluid ounce became 1 ⁄ 128 gal × 231 in 3 /gal × (2.54 cm/in) 3 = 29.5735295625 mL exactly, or about 4% larger than the imperial unit.