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. At the Earth's surface, an object with a mass of 1 slug weighs approximately . 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 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. Related units 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 (but long-obsolete) metric units included the glug (980.665 g) in the centimetre–gram–second system, and the mug, hyl, par, or TME (, 9.80665 kg) in the metre–kilogram–second system. See also British Engineering Units References External links "What is a Slug?" on phy-astr.gsu.edu Imperial units Units of mass Customary units of measurement in the United States