Foot-pound force
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The foot-pound force (symbol: ft·lbf) is an English unit of work or energy. Foot-pound force is the name given as the unit of measure for "kinetic energy" equation. Foot-pound force is frequently abbreviated to foot-pounds.
The foot-pound force equivalent in the international system is, for energy, the joule (J) or, for torque, the newton-meter (N·m). The foot-pound force also has a direct equivalent as a measurement of energy within the non-SI metric system of CGS called the erg.
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[edit] Conversions
1 foot-pound force is equal to:
- 1.355 817 948 331 400 4 joule (J) (exactly)
- 13 558 179.483 314 004 ergs (erg) (exactly)
- ~0.001 285 067 British Thermal Unit IT (BtuIT or BTUIT)
- ~0.323 832 calorie IT (calIT) or ~0.000 323 832 "food calorie" (kcal or Cal)
- ~32.174 049 foot-poundals (ft pdl)
- B*H= torque
[edit] Power
The foot-pound force per minute (ft·lbf/min) and foot-pound force per second (ft·lbf/s) are English units of power derived from the foot-pound force. The English horsepower is defined in terms of it.
- 1 watt (W) ≈ 44.253 728 96 ft·lbf/min
- 1 horsepower (hp) (Imperial mechanical) = 33000 ft·lbf/min = 550 ft·lbf/s
[edit] Unit of work or energy
To calculate a foot-pound force, you can use this formula,
- W = F · d
Where W is work, F is force, and d is distance over which the force is applied (measured in the direction of the force).
[edit] Origins of foot-pound force
The foot-pound force is derived from the original equation of
- Ekin = w · z.
Where Ekin is kinetic energy, w is the weight of the body and z is the average velocity of the falling body times the time of that fall.
These are the factors for w:
- w = m · g / gc
Where w is weight, m is mass, g is the local acceleration of gravity and gc is the dimensional constant.
These are the factors for z:
- z = ½ · v · t
Where as z is the average velocity of the falling body times the time of the fall, ½ is the coefficient to find the average velocity, v is the velocity and t is the time of fall.
When w·z is fully factored to its four units of measure (UOM) then reduced, the two remaining factors left are F and d. With these two variables left, this proves mathematically that energy of motion is force through distance, as in the original experiment of the two falling objects; force though distance
The four UOM are F [force (pound force)], d [distance (foot)], m [mass (pound mass)], t [time (second)].
[edit] Unit of torque
The foot-pound force is also the English unit of torque, which is conventionally expressed in SI units as newton metres rather than joules.
- 1.355 817 948 331 400 4 newton-meter (N·m) (exactly)
As a unit of torque, the order of the units is sometimes reversed, to distinguish from the energy units: pound force-foot (lbf·ft).
[edit] See also
[edit] References
- Sir Isaac Newton, Philosophiae Naturalis Principia Mathematica, Oxford University, July 5th 1686
- Edward F. Obert, Thermodynamics, Mc Graw-Hill Book Co., 1948
- Greg Glover, Terminal Performance, Greg G. Glover, August 2005
- Mc Graw-Hill encyclopedia of Science and Technology, volume ice-lev, 9th Edition, Mc Graw-Hill 2002
