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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 ).
Systems of measure either define mass and derive a force unit or define a base force and derive a mass unit [1] (cf. poundal, a derived unit of force in a mass-based system). A slug is defined as a mass that is accelerated by 1 ft/s 2 when a net force of one pound (lbf) is exerted on it. [2]
In engineering and physics, g c is a unit conversion factor used to convert mass to force or vice versa. [1] It is defined as = In unit systems where force is a derived unit, like in SI units, g c is equal to 1.
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 conversion for the poundal is given by 1 pdl = 1 lb·ft/s 2 = 0.138 254 954 376 N (precisely). [1] To convert between the absolute and gravitational FPS systems one needs to fix the standard acceleration g which relates the pound to the pound-force. [citation needed] =
A force capable of giving a mass of one kilogram an acceleration of one metre per second per second. [32] = 1 N = 1 kg⋅m/s 2: ounce-force: ozf ≡ g 0 × 1 oz = 0.278 013 850 953 781 25 N: pound-force: lbf: ≡ g 0 × 1 lb = 4.448 221 615 2605 N: poundal: pdl ≡ 1 lb⋅ft/s 2 = 0.138 254 954 376 N: short ton-force: tnf [citation needed] ≡ ...
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.
Force required to accelerate a mass of one pound-mass by 1 ft/s 2: 0.1383 N Force pound force: lbf BGS, EEU: Force exerted on a mass of one pound due to gravity 4.448 N Mass slug: BGS mass which, when subjected to a force of one pound-force, accelerates by 1 ft/sec 2: 14.59 kg Mass pound-mass: lbm EEU