The foot-pound force (symbol: ft⋅lbf, ft⋅lb_f, or ft⋅lb ) is a unit of

work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking ** Working animal, an animal t ...

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...

in the

engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...

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 The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...

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 United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. The term ''foot-pound'' is also used as a unit of

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

(see ''

pound-foot (torque) A pound-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. Conversely one pound-foot is the moment about an axis that applies one pound-force at a radius of one ...

''). In the United States this is often used to specify, for example, the tightness of a

fastener A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...

(such as

screw A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to f ...

s and nuts) or the output of an

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

. Although they are dimensionally equivalent, energy (a scalar) and torque (a

Euclidean vector In mathematics, physics, and engineering, a Euclidean vector or simply a vector (sometimes called a geometric vector or spatial vector) is a geometric object that has magnitude (or length) and direction. Vectors can be added to other vectors ...

) 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 In mathematics, the dot product or scalar productThe term ''scalar product'' means literally "product with a scalar as a result". It is also used sometimes for other symmetric bilinear forms, for example in a pseudo-Euclidean space. is an alge ...

of the two, and torque is the

vector product In mathematics, the cross product or vector product (occasionally directed area product, to emphasize its geometric significance) is a binary operation on two vectors in a three-dimensional oriented Euclidean vector space (named here E), and is d ...

. 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: *

s * ergs * about British thermal units * calories * eV = EeV = GeV

Power

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

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...

s *

horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

Related conversions: * 1

≈ ft⋅lbf/min = ft⋅lbf/s * 1

(mechanical) = 33,000 ft⋅lbf/min = 550 ft⋅lbf/s

References

Customary units of measurement in the United States Imperial units Units of energy {{Engineering-stub

Usage

Conversion factors

Energy

Power

See also

References