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One slug is a mass equal to 32.17405 lb (14.59390 kg) based on standard gravity, the international foot, and the avoirdupois pound. [3] In other words, at the Earth's surface (in standard gravity), an object with a mass of 1 slug weighs approximately 32.17405 lbf or 143.1173 N. [ 4 ] [ 5 ]
The unit of substance in the FPS system is the pound-mole (lb-mol) = 273.16 × 10 24. 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.
Since a pound of force (pound force) accelerates a pound of mass at 32.174 049 ft/s 2 (9.80665 m/s 2; the acceleration of gravity, g), we can scale down the unit of force to compensate, giving us one that accelerates 1 pound mass at 1 ft/s 2 rather than at 32.174 049 ft/s 2; and that is the poundal, which is approximately 1 ⁄ 32 pound force.
The pound-force is the product of one avoirdupois pound (exactly 0.45359237 kg) and the standard acceleration due to gravity, approximately 32.174049 ft/s 2 (9.80665 m/s 2). [ 5 ] [ 6 ] [ 7 ] The standard values of acceleration of the standard gravitational field ( g n ) and the international avoirdupois pound (lb) result in a pound-force equal ...
1 pound per square inch (psi) ≈ 6,895 Pa; Torque 1 pound-foot ≈ 1.356 N⋅m; Insulation 1 R-value (ft 2 ⋅°F⋅h/Btu) ≈ 0.1761 R SI (K⋅m 2 /W) Various combination units are in common use; these are straightforwardly defined based on the above basic units. Sizing systems are used for various items in commerce, several of which are U.S ...
In unit systems where force is a derived unit, like in SI units, g c is equal to 1. In unit systems where force is a primary unit, like in imperial and US customary measurement systems , g c may or may not equal 1 depending on the units used, and value other than 1 may be required to obtain correct results. [ 2 ]
≡ 1 g⋅cm 2 /s 2 = 10 −7 J foot-pound force: ft lbf ≡ g 0 × 1 lb × 1 ft = 1.355 817 948 331 4004 J: foot-poundal: ft pdl ≡ 1 lb⋅ft 2 /s 2 = 4.214 011 009 380 48 × 10 −2 J: gallon-atmosphere (imperial) imp gal atm ≡ 1 atm × 1 gal (imp) = 460.632 569 25 J: gallon-atmosphere (US) US gal atm ≡ 1 atm × 1 gal (US) = 383.556 849 ...
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).