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 (cf. ''poundal
'', a derived unit of force in a force-based system). A slug is defined as the mass that is accelerated by 1 ft/s2
when a net force of one pound
(lbf) is exerted on it.
One slug is a mass equal to based on standard gravity
, the international foot
, and the avoirdupois pound
[Shigley, Joseph E. and Mischke, Charles R. ''Mechanical Engineering Design'', Sixth ed, pp. 31–33. McGraw Hill, 2001. .]
At the Earth's surface, an object with a mass of 1 slug exerts a force downward of approximately 32.2 lbf or .
[Shevell, R.S. ''Fundamentals of Flight'', Second ed, p. xix. Prentice-Hall, 1989.]
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 20th century. ''Geepound'' was another name for this unit in early literature.
The name "slug" was coined before 1900 by British physicist Arthur Mason Worthington
, but it did not see any significant use until decades later. It is derived from the meaning "solid block of metal", not from the slug
mollusc. A 1928 textbook says:
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.
The ''blob'' is the inch
version of the slug (1blob is equal to 1 lbf⋅s2
/in, or 12slugs)
[ or equivalent to . This unit is also called ''slinch'' (a portmanteau of the words slug and inch).] Similar terms include ''slugette'' and ''snail''.
Similar metric units include the ''glug'' in the centimetre–gram–second system, and the ''mug'', ''par'', or ''MTE'' in the metre–kilogram–second system.
* British Engineering Units
"What is a Slug?" on phy-astr.gsu.edu
Category:Units of mass