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A pound-foot (lb⋅ft), abbreviated from pound-force foot (lbf · ft), is a unit of torque representing one pound of force acting at a perpendicular distance of one foot from a pivot point. [2] Conversely one foot pound-force (ft · lbf) is the moment about an axis that applies one pound-force at a radius of one foot.
In the US, torque is most commonly referred to as the foot-pound (denoted as either lb-ft or ft-lb) and the inch-pound (denoted as in-lb). [ 17 ] [ 18 ] Practitioners depend on context and the hyphen in the abbreviation to know that these refer to torque and not to energy or moment of mass (as the symbolism ft-lb would properly imply).
Both energy and torque can be expressed as a product of a force vector with a displacement vector (hence pounds and feet); energy is the scalar product of the two, and torque is the vector product. Although calling the torque unit "pound-foot" has been academically suggested, both are still commonly called "foot-pound" in colloquial usage.
Torque; system unit code symbol or abbrev. notes conversion factor/N⋅m combinations Industrial: SI: Newton-metre: Nm N⋅m 1 Nm lbft; Nm lbfft; Non-SI metric: kilogram-metre: kgm kg·m 9.80665 Imperial & US customary: pound-foot: lbft lb⋅ft Pound-inch (lb.in) is also available 1.3558 Scientific: SI: newton metre: Nm N⋅m 1 Nm lbft; Nm ...
As the unit name suggests, it is the product of pounds for the unit of force and feet for the unit of displacement. One joule is approximately equal to 0.7376 ft-lbs. [13] [14] Non-SI units of work include the newton-metre, erg, the foot-pound, the foot-poundal, the kilowatt hour, the litre-atmosphere, and the horsepower-hour.
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).
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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.-specific: US standard clothing size