Inch-pound force

The foot-pound force (symbol: ft⋅lbf, ft⋅lb_f, or ft⋅lb ) is a unit of work or energy in the engineering and Foot–pound–second_system#force, gravitational systems in United States customary units, United States customary and Imperial units, imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement (vector), displacement of one foot (unit), foot. The corresponding SI unit is the joule.

Usage

The foot-pound is often used to specify the muzzle energy of a bullet in small arms ballistics, particularly in the United States.

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 nut (hardware), nuts) or the output of an engine. Although they are dimensional analysis, dimensionally equivalent, energy (a scalar (physics), 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 dot product, scalar product of the two, and torque is the cross product, 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.

Conversion factors

Energy

1 foot pound-force is equivalent to:
* joules
* ergs
* about British thermal units
* calories
* electronvolt, eV = exa-, EeV = electronvolt, GeV

Power

1 foot pound-force per second is equivalent to:
* 1.3558179483314 watts
* horsepower

Related conversions:
* 1 watt ≈ ft⋅lbf/min = ft⋅lbf/s
* 1 horsepower (mechanical) = 33,000 ft⋅lbf/min = 550 ft⋅lbf/s

See also

* Conversion of units#Energy, Conversion of units
* Pound-foot (torque)
* Poundal
* Slug (unit)
* Units of energy

References

Customary units of measurement in the United States
Imperial units
Units of energy

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