Foot-pound (energy) Foot-pound (energy) The foot pound-force (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 upon applying a force of one pound-force (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule. The foot-pound is often used to specify the muzzle energy of a bullet in small arms ballistics, particularly in the United States. "Foot-pound" is also used as a unit of torque (see "pound-foot (torque)"). In the United States this unit is often
Elastic energy of compressible fluids, and especially gases, demonstrates the essence of elastic energy with negligible complication. The simple thermodynamic formula: formula_2 where dU is an infinitesimal change in recoverable internal energy "U", "P" is the uniform pressure (a force per unit area) applied to the material sample of interest, and "dV" is the infinitesimal change in volume that corresponds to the change in internal energy. The minus sign appears because "dV" is negative under compression by a positive applied pressure which also increases the internal energy. Upon reversal, the work that is done "by" a system is the negative of the