Foot-pound force
Encyclopedia
The foot-pound force, or simply foot-pound (symbol: 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 on applying a force
of 1 pound-force
(lbf) through a displacement
of 1 foot. The corresponding SI
unit is the joule
.
of a bullet
in small arms
ballistics
, particularly in the United States
.
"Foot-pound" is sometimes also used as a unit of torque
(see Pound-foot (torque)
). In the United States this unit is often used to specify, for example, the tightness of a bolt
or the output of an engine
. Although they are dimensionally
equivalent, energy (a scalar
), and torque (a 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
of the two, and torque is the cross product
.
s erg
s British Thermal Unit
s gram calorie
s kilogram calories or food calories
Mechanical work
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...
or energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
in the Engineering
English Engineering Units
Some fields of engineering in the United States use a system of measurement of physical quantities known as the English Engineering Units. The system is based on English units of measure.-Definition:...
and Gravitational Systems in United States customary
United States customary units
United States customary units are a system of measurements commonly used in the United States. Many U.S. units are virtually identical to their imperial counterparts, but the U.S. customary system developed from English units used in the British Empire before the system of imperial units was...
and Imperial units of measure. It is the energy transferred on applying a force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
of 1 pound-force
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
(lbf) through a displacement
Displacement (vector)
A displacement is the shortest distance from the initial to the final position of a point P. Thus, it is the length of an imaginary straight path, typically distinct from the path actually travelled by P...
of 1 foot. The corresponding SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
unit is the joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
.
Usage
The foot-pound is often used to specify the muzzle energyMuzzle energy
Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is often used as a rough indication of the destructive potential of a given firearm or load...
of a bullet
Bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...
in small arms
Small arms
Small arms is a term of art used by armed forces to denote infantry weapons an individual soldier may carry. The description is usually limited to revolvers, pistols, submachine guns, carbines, assault rifles, battle rifles, multiple barrel firearms, sniper rifles, squad automatic weapons, light...
ballistics
Ballistics
Ballistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.A ballistic body is a body which is...
, particularly in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
"Foot-pound" is sometimes also used as a unit of torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
(see Pound-foot (torque)
Pound-foot (torque)
A pound-foot is a unit of torque . One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point....
). In the United States this unit is often used to specify, for example, the tightness of a bolt
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
or the output of an engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
. Although they are dimensionally
Dimensional analysis
In physics and all science, dimensional analysis is a tool to find or check relations among physical quantities by using their dimensions. The dimension of a physical quantity is the combination of the basic physical dimensions which describe it; for example, speed has the dimension length per...
equivalent, energy (a scalar
Scalar (physics)
In physics, a scalar is a simple physical quantity that is not changed by coordinate system rotations or translations , or by Lorentz transformations or space-time translations . This is in contrast to a vector...
), and torque (a 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
Dot product
In mathematics, the dot product or scalar product is an algebraic operation that takes two equal-length sequences of numbers and returns a single number obtained by multiplying corresponding entries and then summing those products...
of the two, and torque is the cross product
Cross product
In mathematics, the cross product, vector product, or Gibbs vector product is a binary operation on two vectors in three-dimensional space. It results in a vector which is perpendicular to both of the vectors being multiplied and normal to the plane containing them...
.
Energy units
1 foot-pound is equivalent to: jouleJoule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
s erg
Erg
An erg is the unit of energy and mechanical work in the centimetre-gram-second system of units, symbol "erg". Its name is derived from the Greek ergon, meaning "work"....
s British Thermal Unit
British thermal unit
The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...
s gram calorie
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
s kilogram calories or food calories
Power Units
- 1 wattWattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
≈ ft-lbf/min - 1 horsepowerHorsepowerHorsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
(mechanical) = 33,000 ft-lbf/min = 550 ft-lbf/s
See also
- Pound-foot (torque)Pound-foot (torque)A pound-foot is a unit of torque . One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point....
- PoundalPoundalThe poundal is a unit of force that is part of the foot-pound-second system of units, in Imperial units introduced in 1877, and is from the specialized subsystem of English Absolut ....
- Slug (mass)
- Units of energyUnits of energyBecause energy is defined via work, the SI unit for energy is the same as the unit of work – the joule , named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat...
- Conversion of units