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The foot-pound force (symbol: ft⋅lbf,  ft⋅lbf, or ft⋅lb ) is a unit of work or energy in the engineering and gravitational systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule.
|Unit system||English engineering units and British gravitational system|
|Symbol||ft⋅lbf or ft⋅lb|
|1 ft⋅lbf in ...||... is equal to ...|
|SI units||1.355818 J|
|CGS units||13,558,180 erg|
The term foot-pound is also used as a unit of torque (see pound-foot (torque)). In the United States this is often used to specify, for example, the tightness of a fastener (such as screws and nuts) or the output of an engine. Although they are dimensionally equivalent, energy (a scalar) and torque (a Euclidean vector) are distinct physical quantities. 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. To avoid confusion, it is not uncommon for people to specify each as "foot-pound of energy" or "foot-pound of torque" respectively.
1 foot pound-force is equivalent to:
- 1.355 817 948 331 400 4 joules
- 13558179.483314004 ergs
- about 1.285×10−3 British thermal units
- 0.323832 calories
- 8.462238×10+18 eV = 8.462238 EeV = 8.462238×10+9 GeV
1 foot pound-force per second is equivalent to:
- IEEE Std 260.1™-2004, IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units)
- Fletcher, Leroy S.; Shoup, Terry E. (1978), Introduction to Engineering, Prentice-Hall, ISBN 978-0135018583, LCCN 77024142.: 257
- Budynas, Richard G.; Nisbett, J. Keith (2014-01-27). Mechanical Engineering Design. McGraw Hill Education. ISBN 978-0073529288.