Editing Slug (unit)

{{for|the railway locomotive|Slug (railroad)}}
{{Short description|Unit of mass}}
{{Infobox unit
 |name       = slug
 |image      = 
 |caption    = 
 |standard   = British Gravitational system
 |quantity   = Mass
 |symbol     = slug
 |symbol2    = 
 |namedafter = 
 |extralabel = 
 |extradata  = 
 |units1     = BGS base units
 |inunits1   = 1 ft<sup>−1</sup>⋅lbf⋅s<sup>2</sup>
 |units2     = SI units
 |inunits2   = 14.59390&nbsp;kg
 |units3     = US customary units
 |inunits3   = {{cvt|14.59390|kg|disp=out|sigfig=7}}
}}

The '''slug''' is a derived unit of [[mass]] in a weight-based [[Units of measurement|system of measures]], most notably within the British [[Imperial units|Imperial measurement system]] and the United States [[United States customary units|customary measures system]]. Systems of measure either define mass and derive a force unit ''or'' define a base force and derive a mass unit<ref>See Elementary High School physics and chemistry text books/fundamentals.</ref> (cf. ''[[poundal]]'', a derived unit of force in a mass-based system). A slug is defined as a mass that is accelerated by 1&nbsp;ft/s<sup>2</sup> when a net force of one [[pound (force)|pound]] (lbf) is exerted on it.<ref>{{cite web |last1=Collins |first1=Danielle |title=How to convert between mass and force — in metric and English units |url=https://www.linearmotiontips.com/how-to-convert-between-mass-and-force-in-metric-and-english-units/ |website=Linear Motion Tips |date=May 2019 |access-date=18 January 2021}}</ref>

:<math>
 1~\text{slug}= 1~\text{lbf}{\cdot}\frac{\text{s}^2}{\text{ft}}
 \quad\Longleftrightarrow\quad
 1~\text{lbf}= 1~\text{slug}{\cdot}\frac{\text{ft}}{\text{s}^2}
</math>

One slug is a mass equal to {{convert|32.17405|lb|kg|lk=on|abbr=on}} based on [[standard gravity]], the [[Foot (unit)#International foot|international foot]], and the [[Pound (mass)#Avoirdupois pound|avoirdupois pound]].<ref name=Shigley>Shigley, Joseph E. and Mischke, Charles R. ''Mechanical Engineering Design'', Sixth ed, pp. 31–33. McGraw Hill, 2001. {{ISBN|0-07-365939-8}}.</ref>  In other words, at the Earth's surface (in standard gravity), an object with a mass of 1 slug [[weight|weighs]] approximately {{cvt|32.17405|lbf|N|disp=or}}.<ref>Beckwith, Thomas G., Roy D. Marangoni, et al. ''Mechanical Measurements'', Fifth ed, pp. 34-36. Addison-Wesley Publishing, 1993. {{ISBN|0-201-56947-7}}.</ref><ref name=Shevell>Shevell, R.S. ''Fundamentals of Flight'', Second ed, p. xix. Prentice-Hall, 1989.</ref>

== History ==
The ''slug'' is part of a subset of units known as the [[Foot–pound–second system#Variants|gravitational FPS system]], one of several such specialized systems of mechanical units developed in the late 19th and the early 20th century. ''Geepound'' was another name for this unit in early literature.<ref>[http://www.unit2unit.eu/lb_gee.html gee] {{Webarchive|url=https://web.archive.org/web/20180127202421/http://unit2unit.eu/lb_gee.html |date=2018-01-27 }}. unit2unit.eu</ref>

The name "slug" was coined before 1900 by British physicist [[Arthur Mason Worthington]],<ref>{{cite book |author= Worthington, Arthur Mason |title= Dynamics of Rotation: An Elementary Introduction to Rigid Dynamics |publisher= Longmans, Green, and Co. |year= 1900 |edition= 3rd |page= 9 |url= https://archive.org/stream/dynamicsofrotati00wortuoft#page/8/mode/2up}}</ref> but it did not see any significant use until decades later.<ref>{{Cite book|url=https://books.google.com/books?id=XnRVDwAAQBAJ&q=%22Arthur+Mason+Worthington%22+slug&pg=PA207|title=Encyclopaedia of Historical Metrology, Weights, and Measures: Volume 1|first=Jan|last=Gyllenbok|date=April 11, 2018|publisher=Birkhäuser|isbn=9783319575988|via=Google Books}}</ref> It is derived from the meaning "solid block of metal" (cf. [[Slug (coin)|"slug" fake coin]] or [[Slug (projectile)|"slug" projectile]]), not from the [[slug]] mollusc.<ref>{{Cite web|url=https://books.google.com/books?id=9E4gAQAAIAAJ&q=%22solid+block+of+metal.%22+slug|title=Papers and Presentations|first=Digital Equipment Computer Users|last=Society|date=September 4, 1965|via=Google Books}}</ref> A 1928 textbook says:
{{quote|text=No name has yet been given to the unit of mass and, in fact, as we have developed the theory of dynamics no name is necessary.  Whenever the mass, ''m'', appears in our formulae, we substitute the ratio of the convenient force-acceleration pair ''(w/g)'', and measure the mass in lbs. per ft./sec.<sup>2</sup> or in grams per cm./sec.<sup>2</sup>.|author=Noel Charlton Little, ''College Physics'', Charles Scribner's Sons, 1928, p. 165.}}

{{GravEngAbs}}

The slug is listed in the Regulations under the Weights and Measures (National Standards) Act, 1960. This regulation defines the units of weights and measures, both regular and metric, in Australia.

== Related units ==
The [[inch]] version of the slug (equal to 1&nbsp;lbf⋅s<sup>2</sup>/in, or 12{{nbsp}}slugs) has no official name,<ref name=Shigley/> but is commonly referred to as a ''blob'',<ref>Norton, Robert L. [https://books.google.com/books?id=fK_Q3XNEpMAC&q=blob+mass&pg=PA13 ''Cam Design and Manufacturing Handbook'', p. 13.] Industrial Press Inc., 2009. {{ISBN|0831133678}}.</ref> ''slinch'' (a [[portmanteau]] of the words slug and inch),<ref>[http://www.diracdelta.co.uk/science/source/s/l/slug/source.html Slug] {{Webarchive|url=https://web.archive.org/web/20161130034640/http://www.diracdelta.co.uk/science/source/s/l/slug/source.html |date=2016-11-30 }}. DiracDelta Science & Engineering Encyclopedia</ref><ref name=Wolframblob>{{cite web |title=1 blob |url=http://www.wolframalpha.com/input/?i=1+blob&lk=1 |work=Wolfram Alpha Computational Knowledge Engine |access-date=27 October 2011}}</ref> ''slugette'',<ref>Celmer, Robert. ''Notes to Accompany Vibrations II''. Version 2.2. 2009.</ref> or ''snail''.<ref>Rowlett, Russ. [http://www.unc.edu/~rowlett/units/dictS.html "How Many? A Dictionary of Units of Measurement"]. unc.edu, September 1, 2004. Retrieved January 26, 2018.</ref> It is equivalent to {{convert|386.0886|lb}} based on standard gravity.<ref name=Shigley/>

Similar (but long-obsolete) metric units included the ''glug'' (980.665&nbsp;g) in a gravitational system related to the [[centimetre–gram–second system of units|centimetre–gram–second system]],<ref>{{cite book |last=Cardarelli |first=François |title=Encyclopaedia of Scientific Units, Weights and Measures |url=https://archive.org/details/encyclopaediaofs0000card |url-access=registration |pages=[https://archive.org/details/encyclopaediaofs0000card/page/358 358], 377 |year=1999 |publisher=Springer |isbn=1-85233-682-X}}</ref><ref>{{cite journal |title= Beware of the "Glug," a New Unit of Mass! |year= 1958 |last1= David |first1= A. |journal= American Journal of Physics |volume= 26 |issue= 1 |page= 41 |department= Letters to the Editor |doi= 10.1119/1.1934599 }}</ref> and the ''mug'', ''[[hyl (unit)|hyl]]'', ''par'', or ''TME'' ({{Langx|de|technische Masseneinheit|lit=technical mass unit}}, 9.80665&nbsp;kg) in a [[Gravitational metric system|gravitational system]] related to the [[MKS system of units|metre–kilogram–second system]].<ref>{{cite book |last=Cardarelli |first=François |title=Encyclopaedia of Scientific Units, Weights and Measures |url=https://archive.org/details/encyclopaediaofs0000card |url-access=registration |pages=[https://archive.org/details/encyclopaediaofs0000card/page/470 470], 497 |year=1999 |publisher=Springer |isbn=1-85233-682-X}}</ref>

==See also==
* [[English Engineering Units#British Engineering Units|British Engineering Units]]

== References ==
{{Reflist}}

==External links==
* [http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/slug.html "What is a Slug?" on phy-astr.gsu.edu]

{{Imperial units}}

[[Category:Imperial units]]
[[Category:Units of mass]]
[[Category:Customary units of measurement in the United States]]