The force that a mass m experiences due to gravity of another mass,

where g is the acceleration due to gravity. (Note that this formula is a special case of Newton's second law.) The weight is therefore an extrinsic property depending on the strength of gravitational acceleration to which a body is subjected (and so would be smaller at the top of a mountain than at the mountain's foot), while mass is an intrinsic property. While no less an authority than the National Institute of Standards and Technology notes that "in commercial and everyday one, and especially in common parlance, weight is usually used as a synonym for mass" (Taylor 1995, p. 24), this extremely confusing practice should be universally discouraged.

The unit of force in the MKS system is the newton. The foot-pound-second system of units defines a weight, the pound (or, more explicitly, the pound-force), as the basic unit, with mass (measured in slugs, or occasionally pound-masses) a derived unit. Other units of weight include the kilopond and poundal.

Bag, Force, Gravity, Kilopond, Mass, Metric Ton, Pound, Poundal, Pound-Force, Pound-Mass, Slug, Stone, Ton, Weight