User:Milton Beychok/Sandbox2: Difference between revisions

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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 '''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>'''''). It is used primarily in the [[United States]] and is equivalent to exactly 4.4482216152605 [[newton]]s.  


== Definitions ==
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].
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 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>).
 
 
 
 
==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>
}}
 
==References==

Revision as of 14:44, 5 July 2011

The pound-force (symbol: lbf [Note 1] ) is a measurement unit of force which will accelerate 1 pound of mass to 9.80665 m/s2 (≈ 32.17405 ft/s2), the standard average acceleration due to gravity on Earth's surface (referred to as gn). It is used primarily in the United States and is equivalent to exactly 4.4482216152605 newtons.

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].



Notes

  1. ↑ The symbol lbf is derived from the Latin libra for "pound" and the symbol f for "force")

References

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