Foot-pound force
In physics, a foot-pound force (symbol ft·lbf or ft·lbf), usually abbreviated to foot-pound, is an Imperial and U.S. customary unit of mechanical work, or energy, although in scientific fields one commonly uses the equivalent metric unit of the joule (J). There are approximately 1.356 J/ft·lbf, or exactly 1.355 817 948 331 400 4 J/ft·lbf.
To calculate a foot-pound, you can use this formula,
- W = F × D
where W is work (in foot-pounds), F is force (in pounds), and D is distance (in feet) over which the force is applied (measured in the direction of the force).
The foot-pound [force] is also the unit of torque, which is conventionally expressed in SI units as newton-meters rather than joules. Sometimes the order of the units is reversed for torque, expressed as pound-feet rather than foot pounds.
Doing 550 foot-pounds of work on an object in one second is equal to a horsepower, an Imperial and U.S. customary unit of power.
Strictly speaking, the foot-pound is a different unit, having the dimensions of length×mass, rather than the foot-pound force's length×mass×acceleration, but it has few applications, which is why the abbreviation of "foot-pound force" to "foot-pound" is rarely a problem.