User:Milton Beychok/Sandbox2: Difference between revisions

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A '''kilogram-force''' ('''kgf''') is a unit of [[force]] which will [[acceleration|accelerate]] 1 [[kilogram]] of [[mass]] to 9.80665 [[metre|m]]/[[second|s]]<sup>2</sup>, the standard average [[acceleration due to gravity]] on [[Earth]]'s surface (referred to as '''''g<sub>n</sub>''''').<ref name=NIST-gravity/> Since a [[Newton (unit)|newton]] is defined<ref name=NASA/><ref name=NIST-newton/> as the force which will accelerate 1 kilogram  of mass to 1 m/s<sup>2</sup>, one  kilogram-force is by definition equal to 9.80665 [[newton (unit)|newtons]].  
The '''pound-force''' (symbol: '''lbf''' from the Latin ''libra'' for [[Pound (mass)|pound]] and the symbol ''f'' for [[force]]) is a [[measurement]]|unit of force used primarily in the [[United States]].  It is equivalent to exactly 4.4482216152605 [[newton]]s. In most contexts, the shorter name '''"pound"''' is used, but this can introduce confusion with the [[pound (mass)|mass unit of the similar name]].


The kilogram-force was not very well defined until the 3rd [[General Conference on Weights and Measures]] (Conférence Générale des Poids et Mesures, CGPM) defined '''''g<sub>n</sub>''''', the standard gravity, to be 9.80665 m/s<sup>2</sup> in 1901.<ref name=GCPM3/> Although it was once widely used, it has never been part of the [[International System of Units]] (SI) introduced in 1960 by the 11th GCPM.<ref name=GCPM11/>
== Definitions ==
The pound-force is equal to the gravitational force exerted on a mass of one [[Pound_(mass)#Avoirdupois_pound|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 [[gravity (Earth)|Earth's gravity]] (which varies from place to place by up to half a percent) can safely be neglected.


The kilogram-force is still used to some extent in a few countries, but it is generally considered to be obsolete in most countries.
The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. Today, in accordance with the [[General Conference on Weights and Measures]], [[standard gravity]] is usually taken to be 9.80665&nbsp;m/s<sup>2</sup> (32.174 049&nbsp;ft/s<sup>2</sup>).
 
==Equivalent units of force==
 
*1 kgf ≡ 9.80665 newton (symbol: '''N''')
*1 kgf ≡ 980,665 dyne (symbol: '''dyn''')
*1 kgf ≡ 1 kilopond (symbol: '''kp''')
*1 kgf ≡ 9.80665×10<sup>-3</sup> sthène (symbol: '''sn''')
*1 kgf ≈ 2.20462 pound-force (symbol: '''lbf''')
*1 kgf ≈ 2.20462×10<sup>-3</sup> kip (symbol: '''kip''')
*1 kgf ≈ 70.93164 poundal (symbol: '''pdl''')
 
==References==
{{Reflist|refs=
 
<ref name=NIST-gravity>[http://physics.nist.gov/Pubs/SP330/sp330.pdf The International System of Units (SI), NIST Special Publication 330, 2008 Edition] (pdf page 57 of 77 pdf pages)</ref>
 
<ref name=NASA>[http://www-istp.gsfc.nasa.gov/stargaze/Sgloss.htm#q56 Glossary] From the website of [[NASA]]'s [[Goddard Space Flight Center]].</ref>
 
<ref name=NIST-newton>[http://physics.nist.gov/Pubs/SP330/sp330.pdf The International System of Units (SI), NIST Special Publication 330, 2008 Edition] (pdf page 30 of 77 pdf pages)</ref>
 
<ref name=GCPM3>[http://www.bipm.org/en/CGPM/db/3/2/ Resolution of the 3rd meeting of the CGPM (1901)]</ref>
 
<ref name=GCPM11>[http://www.bipm.org/en/CGPM/db/11/12/ Resolution 12 of the 11th meeting of the CGPM (1960)]</ref>
}}

Revision as of 12:24, 5 July 2011

The pound-force (symbol: lbf from the Latin libra for pound and the symbol f for force) is a measurement|unit of force used primarily in the United States. It is equivalent to exactly 4.4482216152605 newtons. In most contexts, the shorter name "pound" is used, but this can introduce confusion with the mass unit of the similar name.

Definitions

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 place to place by up to half a percent) can safely be neglected.

The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. Today, in accordance with the General Conference on Weights and Measures, standard gravity is usually taken to be 9.80665 m/s2 (32.174 049 ft/s2).

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