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The slug is a derived unit of mass in a weight-based system of measures, most notably within the British Imperial measurement system and the United States 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 ft/s2 when a net force of one pound (lbf) is exerted on it.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</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 Template:Convert based on standard gravity, the international foot, and the avoirdupois pound.<ref name=Shigley>Shigley, Joseph E. and Mischke, Charles R. Mechanical Engineering Design, Sixth ed, pp. 31–33. McGraw Hill, 2001. Template:ISBN.</ref> In other words, at the Earth's surface (in standard gravity), an object with a mass of 1 slug weighs approximately Template:Cvt.<ref>Beckwith, Thomas G., Roy D. Marangoni, et al. Mechanical Measurements, Fifth ed, pp. 34-36. Addison-Wesley Publishing, 1993. Template:ISBN.</ref><ref name=Shevell>Shevell, R.S. Fundamentals of Flight, Second ed, p. xix. Prentice-Hall, 1989.</ref>
HistoryEdit
The slug is part of a subset of units known as the 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>gee Template:Webarchive. unit2unit.eu</ref>
The name "slug" was coined before 1900 by British physicist Arthur Mason Worthington,<ref>Template:Cite book</ref> but it did not see any significant use until decades later.<ref>Template:Cite book</ref> It is derived from the meaning "solid block of metal" (cf. "slug" fake coin or "slug" projectile), not from the slug mollusc.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A 1928 textbook says: Template:Quote
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 unitsEdit
The inch version of the slug (equal to 1 lbf⋅s2/in, or 12Template:Nbspslugs) has no official name,<ref name=Shigley/> but is commonly referred to as a blob,<ref>Norton, Robert L. Cam Design and Manufacturing Handbook, p. 13. Industrial Press Inc., 2009. Template:ISBN.</ref> slinch (a portmanteau of the words slug and inch),<ref>Slug Template:Webarchive. DiracDelta Science & Engineering Encyclopedia</ref><ref name=Wolframblob>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> slugette,<ref>Celmer, Robert. Notes to Accompany Vibrations II. Version 2.2. 2009.</ref> or snail.<ref>Rowlett, Russ. "How Many? A Dictionary of Units of Measurement". unc.edu, September 1, 2004. Retrieved January 26, 2018.</ref> It is equivalent to Template:Convert based on standard gravity.<ref name=Shigley/>
Similar (but long-obsolete) metric units included the glug (980.665 g) in a gravitational system related to the centimetre–gram–second system,<ref>Template:Cite book</ref><ref>Template:Cite journal</ref> and the mug, hyl, par, or TME (Template:Langx, 9.80665 kg) in a gravitational system related to the metre–kilogram–second system.<ref>Template:Cite book</ref>