Slug
The slug is a unit of mass used primarily in the U.S. customary system and British engineering contexts.
1 slug = 32.174 pounds (lb) (mass)
Equivalent to approximately 14.5939 kilograms (kg)
Defined so that when a force of one pound-force (lbf) acts on a mass of one slug, it accelerates at 1 ft/s² (using F=ma in imperial units).
Key Facts:
Used mainly in physics and engineering for calculations involving Newton’s second law in imperial units
Allows consistent use of pound-force and pound-mass without extra conversion factors
Useful in dynamics, ballistics, and engineering mechanics
The slug bridges the gap between force and mass in the imperial system, making calculations easier when using pound-force units.
Grain [gr]
The grain (gr) is one of the oldest units of mass, traditionally used in various weight systems including troy, apothecary, and avoirdupois.
One grain is defined as exactly 64.79891 milligrams (0.0648 grams). It was originally based on the weight of a single grain of barley or wheat.
Grains are still commonly used today to measure small quantities such as the weight of bullets, arrows, and some pharmaceuticals.
Summary:
1 grain = 64.79891 milligrams (0.0648 grams)
Used in troy, apothecary, and avoirdupois systems
Common in ammunition and medicine measurements