Pound-force should not be confused with pound-mass (lb), often simply called pound, which is a unit of mass, nor should these be confused with foot-pound (ft⋅lbf), a unit of energy, or pound-foot (lbf⋅ft), a unit of torque.
The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from equator to pole by up to half a percent) can safely be neglected.[4]
The 20th century, however, brought the need for a more precise definition, requiring a standardized value for acceleration due to gravity.
The standard values of acceleration of the standard gravitational field (gn) and the international avoirdupois pound (lb) result in a pound-force equal to 4.4482216152605 N.[b]
This definition can be rephrased in terms of the slug. A slug has a mass of 32.174049 lb. A pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s2, so:
In some contexts, the term "pound" is used almost exclusively to refer to the unit of force and not the unit of mass. In those applications, the preferred unit of mass is the slug, i.e. lbf⋅s2/ft. In other contexts, the unit "pound" refers to a unit of mass. The international standard symbol for the pound as a unit of mass is lb.[8]
Three approaches to units of mass and force or weight[9][10]
In the "engineering" systems (middle column), the weight of the mass unit (pound-mass) on Earth's surface is approximately equal to the force unit (pound-force). This is convenient because one pound mass exerts one pound force due to gravity. Note, however, unlike the other systems the force unit is not equal to the mass unit multiplied by the acceleration unit[11]—the use of Newton's second law, F = m ⋅ a, requires another factor, gc, usually taken to be 32.174049 (lb⋅ft)/(lbf⋅s2). "Absolute" systems are coherent systems of units: by using the slug as the unit of mass, the "gravitational" FPS system (left column) avoids the need for such a constant. The SI is an "absolute" metric system with kilogram and meter as base units.
The term pound of thrust is an alternative name for pound-force in specific contexts. It is frequently seen in US sources on jet engines and rocketry, some of which continue to use the FPS notation. For example, the thrust produced by each of the Space Shuttle's two Solid Rocket Boosters was 3,300,000 pounds-force (14.7 MN), together 6,600,000 pounds-force (29.4 MN).[12][13]
^IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1™-2004 (Revision of IEEE Std 260.1-1993)
^Fletcher, Leroy S.; Shoup, Terry E. (1978), Introduction to Engineering, Prentice-Hall, ISBN978-0135018583, LCCN 77024142, from the original on 2019-12-06, retrieved 2017-08-03.: 257
^"Mass and Weight". engineeringtoolbox.com. from the original on 2010-08-18. Retrieved 2010-08-03.
^Acceleration due to gravity varies over the surface of the Earth, generally increasing from about 9.78 m/s2 (32.1 ft/s2) at the equator to about 9.83 m/s2 (32.3 ft/s2) at the poles.
^BS 350 : Part 1: 1974 Conversion factors and tables, Part 1. Basis of tables. Conversion factors. British Standards Institution. 1974. p. 43.
^In 1901 the third CGPM 2012-02-07 at the Wayback Machine declared (second resolution) that:
The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980.665 cm/s2, value already stated in the laws of some countries.
This value was the conventional reference for calculating the kilogram-force, a unit of force whose use has been deprecated since the introduction of SI.
^Barry N. Taylor, Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811, Appendix B note 24
^IEEE Std 260.1™-2004, IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units)
^Comings, E. W. (1940). "English Engineering Units and Their Dimensions". Industrial & Engineering Chemistry. 32 (7): 984–987. doi:10.1021/ie50367a028.
^Klinkenberg, Adrian (1969). "The American Engineering System of Units and Its Dimensional Constant gc". Industrial & Engineering Chemistry. 61 (4): 53–59. doi:10.1021/ie50712a010.
^The acceleration unit is the distance unit divided by the time unit squared.
^"Space Launchers - Space Shuttle". www.braeunig.us. from the original on 6 April 2018. Retrieved 16 February 2018. Thrust: combined thrust 29.36 MN SL (maximum thrust at launch reducing by 1/3 after 50 s)
^Richard Martin (12 January 2001). "From Russia, With 1 Million Pounds of Thrust". wired.com. from the original on 25 September 2019. Retrieved 25 November 2019.
General sources
Obert, Edward F. (1948). Thermodynamics. New York: D. J. Leggett Book Company. Chapter I "Survey of Dimensions and Units", pp. 1-24.
April 21, 2023
pound, force, look, pound, force, pound, wiktionary, free, dictionary, redirects, here, airport, north, platte, nebraska, assigned, iata, code, north, platte, regional, airport, unit, mass, pound, mass, basis, weight, paper, paper, density, monetary, unit, pou. Look up pound force or pound in Wiktionary the free dictionary lbf redirects here For the airport in North Platte Nebraska assigned the IATA code LBF see North Platte Regional Airport For the unit of mass see Pound mass For the basis weight of paper see Paper density For the monetary unit see Pound currency The pound of force or pound force symbol lbf 1 sometimes lbf 2 is a unit of force used in some systems of measurement including English Engineering units a and the foot pound second system 3 Pound forceUnit systemEnglish Engineering units British Gravitational SystemSymbollbfConversions1 lbf in is equal to SI units 4 448222 N CGS units 444 822 2 dyn Absolute English System 32 17405 pdlPound force should not be confused with pound mass lb often simply called pound which is a unit of mass nor should these be confused with foot pound ft lbf a unit of energy or pound foot lbf ft a unit of torque Contents 1 Definitions 1 1 Product of avoirdupois pound and standard gravity 2 Conversion to other units 3 Foot pound second FPS systems of units 4 Pound of thrust 5 See also 6 Notes and references 7 General sourcesDefinitions EditThe pound force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth Since the 18th century the unit has been used in low precision measurements for which small changes in Earth s gravity which varies from equator to pole by up to half a percent can safely be neglected 4 The 20th century however brought the need for a more precise definition requiring a standardized value for acceleration due to gravity Product of avoirdupois pound and standard gravity Edit The pound force is the product of one avoirdupois pound exactly 0 45359237 kg and the standard acceleration due to gravity 9 80665 m s2 32 174049 ft s2 5 6 7 The standard values of acceleration of the standard gravitational field gn and the international avoirdupois pound lb result in a pound force equal to 4 4482216152605 N b 1 lbf 1 lb g n 1 lb 9 80665 m s 2 0 3048 m ft 1 lb 32 174049 f t s 2 32 174049 f t l b s 2 1 lbf 1 lb 0 45359237 kg lb g n 0 45359237 kg 9 80665 m s 2 4 4482216152605 N displaystyle begin aligned 1 text lbf amp 1 text lb times g text n amp 1 text lb times 9 80665 tfrac text m text s 2 0 3048 tfrac text m text ft amp approx 1 text lb times 32 174049 mathrm tfrac ft s 2 amp approx 32 174049 mathrm tfrac ft cdot lb s 2 1 text lbf amp 1 text lb times 0 45359237 tfrac text kg text lb times g text n amp 0 45359237 text kg times 9 80665 tfrac text m text s 2 amp 4 4482216152605 text N end aligned This definition can be rephrased in terms of the slug A slug has a mass of 32 174049 lb A pound force is the amount of force required to accelerate a slug at a rate of 1 ft s2 so 1 lbf 1 slug 1 ft s 2 1 slug ft s 2 displaystyle begin aligned 1 text lbf amp 1 text slug times 1 tfrac text ft text s 2 amp 1 tfrac text slug cdot text ft text s 2 end aligned Conversion to other units EditUnits of force vte newton dyne kilogram force kilopond pound force poundal1 N 1 kg m s2 105 dyn 0 10197 kp 0 22481 lbf 7 2330 pdl1 dyn 10 5 N 1 g cm s2 1 0197 10 6 kp 2 2481 10 6 lbf 7 2330 10 5 pdl1 kp 9 80665 N 980665 dyn gn 1 kg 2 2046 lbf 70 932 pdl1 lbf 4 448222 N 444822 dyn 0 45359 kp gn 1 lb 32 174 pdl 1 pdl 0 138255 N 13825 dyn 0 014098 kp 0 031081 lbf 1 lb ft s2The value of gn as used in the official definition of the kilogram force 9 80665 m s2 is used here for all gravitational units Foot pound second FPS systems of units EditMain article Foot pound second system In some contexts the term pound is used almost exclusively to refer to the unit of force and not the unit of mass In those applications the preferred unit of mass is the slug i e lbf s2 ft In other contexts the unit pound refers to a unit of mass The international standard symbol for the pound as a unit of mass is lb 8 Three approaches to units of mass and force or weight 9 10 vte Base Force Weight Mass2nd law of motion m F a F W a g F m aSystem BG GM EE M AE CGS MTS SIAcceleration a ft s2 m s2 ft s2 m s2 ft s2 Gal m s2 m s2Mass m slug hyl pound mass kilogram pound gram tonne kilogramForce F weight W pound kilopond pound force kilopond poundal dyne sthene newtonPressure p pound per square inch technical atmosphere pound force per square inch standard atmosphere poundal per square foot barye pieze pascalIn the engineering systems middle column the weight of the mass unit pound mass on Earth s surface is approximately equal to the force unit pound force This is convenient because one pound mass exerts one pound force due to gravity Note however unlike the other systems the force unit is not equal to the mass unit multiplied by the acceleration unit 11 the use of Newton s second law F m a requires another factor gc usually taken to be 32 174049 lb ft lbf s2 Absolute systems are coherent systems of units by using the slug as the unit of mass the gravitational FPS system left column avoids the need for such a constant The SI is an absolute metric system with kilogram and meter as base units Pound of thrust EditFurther information thrust The term pound of thrust is an alternative name for pound force in specific contexts It is frequently seen in US sources on jet engines and rocketry some of which continue to use the FPS notation For example the thrust produced by each of the Space Shuttle s two Solid Rocket Boosters was 3 300 000 pounds force 14 7 MN together 6 600 000 pounds force 29 4 MN 12 13 See also EditFoot pound energy Ton force Kip unit Mass in general relativity Mass in special relativity Mass versus weight for the difference between the two physical properties Newton Poundal Pounds per square inch a unit of pressureNotes and references Edit Despite its name this system is based on United States customary units and is only used in the US The international avoirdupois pound is defined to be exactly 0 453592 37 kg IEEE Standard Letter Symbols for Units of Measurement SI Units Customary Inch Pound Units and Certain Other Units IEEE Std 260 1 2004 Revision of IEEE Std 260 1 1993 Fletcher Leroy S Shoup Terry E 1978 Introduction to Engineering Prentice Hall ISBN 978 0135018583 LCCN 77024142 archived from the original on 2019 12 06 retrieved 2017 08 03 257 Mass and Weight engineeringtoolbox com Archived from the original on 2010 08 18 Retrieved 2010 08 03 Acceleration due to gravity varies over the surface of the Earth generally increasing from about 9 78 m s2 32 1 ft s2 at the equator to about 9 83 m s2 32 3 ft s2 at the poles BS 350 Part 1 1974 Conversion factors and tables Part 1 Basis of tables Conversion factors British Standards Institution 1974 p 43 In 1901 the third CGPM Archived 2012 02 07 at the Wayback Machine declared second resolution that The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth s gravity is 980 665 cm s2 value already stated in the laws of some countries This value was the conventional reference for calculating the kilogram force a unit of force whose use has been deprecated since the introduction of SI Barry N Taylor Guide for the Use of the International System of Units SI 1995 NIST Special Publication 811 Appendix B note 24 IEEE Std 260 1 2004 IEEE Standard Letter Symbols for Units of Measurement SI Units Customary Inch Pound Units and Certain Other Units Comings E W 1940 English Engineering Units and Their Dimensions Industrial amp Engineering Chemistry 32 7 984 987 doi 10 1021 ie50367a028 Klinkenberg Adrian 1969 The American Engineering System of Units and Its Dimensional Constant gc Industrial amp Engineering Chemistry 61 4 53 59 doi 10 1021 ie50712a010 The acceleration unit is the distance unit divided by the time unit squared Space Launchers Space Shuttle www braeunig us Archived from the original on 6 April 2018 Retrieved 16 February 2018 Thrust combined thrust 29 36 MN SL maximum thrust at launch reducing by 1 3 after 50 s Richard Martin 12 January 2001 From Russia With 1 Million Pounds of Thrust wired com Archived from the original on 25 September 2019 Retrieved 25 November 2019 General sources EditObert Edward F 1948 Thermodynamics New York D J Leggett Book Company Chapter I Survey of Dimensions and Units pp 1 24 Retrieved from https en wikipedia org w index php title Pound force amp oldid 1118709172, wikipedia, wiki, book, books, library,
