The slug is a derived unit of
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
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 mass-based system). A slug is defined as a mass that is accelerated by 1 ft/s
2 when a net force of one
pound (lbf) is exerted on it.
:
One slug is a mass equal to based on
standard gravity
The standard acceleration of gravity or standard acceleration of free fall, often called simply standard gravity and denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is a constant ...
, 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. .] In other words, at the Earth's surface (in standard gravity), an object with a mass of 1 slug
weighs approximately .
[Shevell, R.S. ''Fundamentals of Flight'', Second ed, p. xix. Prentice-Hall, 1989.]
History
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.
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" (cf.
"slug" fake coin or
"slug" projectile), not from the
slug
Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...
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.
Related units
The
inch
The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
version of the slug (equal to 1 lbf⋅s
2/in, or 12slugs) has no official name,
[ but is commonly referred to as a ''blob'', ''slinch'' (a ]portmanteau
In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together. of the words slug and inch),[
Similar (but long-obsolete) metric units included the ''glug'' (980.665 g) in a gravitational system related to the centimetre–gram–second system, and the ''mug'', '' hyl'', ''par'', or ''TME'' (, 9.80665 kg) in a gravitational system related to the metre–kilogram–second system.]
See also
* British Engineering Units
References
External links
"What is a Slug?" on phy-astr.gsu.edu
{{Imperial units
Imperial units
Units of mass
Customary units of measurement in the United States