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The pound per square inch (abbreviation: psi) or, more accurately, pound-force per square inch (symbol: lbf/in2 ), [ 1] is a unit of measurement of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force with magnitude of one pound-force applied to an area of one square inch.
The unit, named after Blaise Pascal, is an SI coherent derived unit defined as one newton per square metre (N/m 2). [1] It is also equivalent to 10 barye (10 Ba) in the CGS system. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar , and the kilopascal (1 kPa = 1000 Pa), which is equal to ...
This is convenient because one pound mass exerts one pound force due to gravity. Note, however, unlike the other systems the force unit is not equal to the mass unit multiplied by the acceleration unit [ 11 ] —the use of Newton's second law , F = m ⋅ a , requires another factor, g c , usually taken to be 32.174049 (lb⋅ft)/(lbf⋅s 2 ).
The English Engineering Units is a system of coherent units used in the United States. The set is defined by the following units, [3] and definitive conversions to the International System of Units. [4] Units for other physical quantities are derived from this set as needed. In English Engineering Units, the pound-mass and the pound-force are ...
The unit of substance in the FPS system is the pound-mole (lb-mol) = 273.16 × 1024. Until the SI decided to adopt the gram-mole, the mole was directly derived from the mass unit as (mass unit)/ (atomic mass unit). The unit (lbf⋅s 2 /ft)-mol also appears in a former definition of the atmosphere.
The poundal (symbol: pdl) is a unit of force, introduced in 1877, that is part of the Absolute English system of units, which itself is a coherent subsystem of the foot–pound–second system . The poundal is defined as the force necessary to accelerate 1 pound-mass at 1 foot per second squared. [ 1]: 54 1 pdl = 0.138 254 954 376 N exactly.
Mass 1 slug = 1 lbf⋅s 2 /ft ≈ 14.59390 kg; Force 1 poundal = force to accelerate 1 pound mass 1 foot/second/second ≈ 0.138 newtons. 1 kip = 1000 lbf ≈ 4.44822 kN; Energy 1 foot-pound ≈ 1.356 J; 1 British thermal unit (Btu) ≈ 1.055 kJ (1,054–1,060 J, depending on which of several definitions of BTU is used)
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 ).