User:Milton Beychok/Sandbox2: Difference between revisions

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The '''pound-force''' (symbol: '''lbf'''&thinsp;<ref name=lbf group=note/>&thinsp;) is a [[measurement]] unit of [[force]] which will [[acceleration|accelerate]] 1 [[Pound (mass)|pound]] of [[mass]] to 9.80665 [[metre|m]]/[[second|s]]<sup>2</sup> (≈&thinsp;32.17405 [[foot|ft]]/[[second|s]]<sup>2</sup>), the standard average [[acceleration due to gravity]] on [[Earth]]'s surface (referred to as '''''g<sub>n</sub>'''''&thinsp;<ref name=GCPM3/>). It is used primarily in the [[United States]] and is equivalent to exactly 4.4482216152605 [[newton]]s.<ref name=NIST-lbf/>


In common usage and other contexts, it is most often referred to in the United States as a '''''pound''''' or as '''''lb''''', but this can lead to  confusion with the [[pound (mass)|pound-mass]].
==Definition in terms of the SI unit of force==
The newton (symbol: N) is the unit of force named in the [[International System of Units]] (SI). Using the standard average acceleration due to gravity, denoted '''''g<sub>n</sub>''''', as being 9.80665 m/s<sup>2</sup> and the internationally agreed upon definition of the pound-mass, denoted as '''''lbm''''', as being 0.45359237 [[Kilogram|kg]],<ref name=GCPM3/><ref name=NBS/> we can determine the number of newtons exactly equivalent to a pound-force:
:<math>\begin{align}1\,\mathrm{lbf} &\equiv 1\,\mathrm{lbm} \cdot g_n \\
&\equiv 0.45359237\,\mathrm{kg} \cdot 9.80665\,\mathrm{{m}/{s^2}}\\
&\equiv 4.4482216152605\,\mathrm{N} \end{align}</math>
==Equivalent units of force==
*1 lbf &asymp; 4.448221 newton (symbol: '''N''')
*1 lbf &asymp; 4448822 [[dyne]] (symbol: '''dyn''')
*1 lbf &asymp; 0.453592 [[kilogram-force]] (symbol: '''kgf''')
*1 lbf &asymp; 0.453592 [[Kilogram-force|kilopond]] (symbol: '''kp''')<ref name=kp group=note/>
*1 lbf &asymp; 4.448221×10<sup>−3</sup> [[sthène]] (symbol: '''sn''')
*1 lbf &asymp; 32.17405 [[poundal]] (symbol: '''pdl''')
*1 lbf &equiv; 0.001 [[kip]]  (symbol: '''kip''')<ref name=kip group=note/>
==Notes==
{{reflist|group=note|refs=
<ref name=lbf group=note>The symbol '''lbf''' is derived from the Latin ''libra'' for "pound" and the symbol ''f'' for "force")</ref>
<ref name=kp group=note> Another name for a kilogram-force. Not to be confused with "kilopounds", meaning 1,000 pounds of mass.</ref>
<ref name=kip group=note>A non-SI unit of force equal to 1,000 pound-force.</ref>
}}
==References==
{{Reflist|refs=
<ref name=GCPM3>[http://www.bipm.org/en/CGPM/db/3/2/ Resolution of the 3rd meeting of the CGPM (1901)] Definition of the standard average acceleration due to gravity</ref>
<ref name=NBS>[http://physics.nist.gov/Pubs/SP447/app8.pdf Appendix 8, Customary System of Weights and Measures] [[U.S. Dept. of Commerce]], July 15, 1968. Definition of the pound-mass.</ref>
<ref name=NIST-lbf>[http://wtc.nist.gov/progress_report_june04/metric_conversion.pdf Metric Conversion Table] Scroll down to "Force"</ref>
}}

Revision as of 15:59, 6 July 2011

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