Foot-pound (energy)

Not to be confused with Pound-foot (torque) or Foot-poundal.

The foot-pound force, or simply foot-pound (symbol: ft-lb_f or ft-lb) is a unit of work or energy in the English Engineering Units 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 (lb_f) through a displacement of 1 foot (ft). The corresponding SI unit is the Joule.

Usage

The foot-pound is a term used particularly in the United States. The foot-pound is often used to specify the muzzle energy of a bullet in small arm ballistics, the tightness of a bolt and the output of an internal combustion engine.

The foot-pound can be expressed either as energy or torque. Although they are dimensionally equivalent, energy (a scalar), and torque (a vector) are distinct physical quantities.

Energy

When the foot-pound is expressed as an integral of force and displacement it arises from a dot product. Muzzle energy and the chemical energy released by liquid fuel in an internal combustion engine are examples of the dot product.

Torque

The "Foot-pound" is also the name of a unit of torque (see Pound-foot (torque)). Torque is the product of a force vector with a displacement vector and is a cross product. The measurement of a torque wrench or engine torque are examples of the cross product.

Conversion to other units

Energy units

1 foot-pound is equivalent to:

• 1.3558179483314004 joules (exactly)^{[note 1]}
• 0.001285067 British thermal units
• 0.323832 gram calories
• 0.000323832 kilogram calories or food calories

Power units

• 1 watt ≈ 44.25372896 ft-lb_f/min
• 1 horsepower (mechanical) = 33,000 ft-lb_f/min = 550 ft-lb_f/s

See also

• Pound-foot (torque)
• Poundal
• Slug (mass)
• Units of energy
• Conversion of units

Notes

1. ^ This is the product of the international pound (0.45359237 kg), standard gravity (9.80665 m/s²) and the international foot (0.3048 m)