n. (Continuum mechanics) a primitive concept in mechanics, that is assumed to be additive for disjoint bodies and, in Newtonian dynamics, to be constant for a given set of particles that may either constitute a body or be discrete. It is standardly measured in kilograms, and in practice the mass of a body is found by measuring its weight. Formally, mass is a measure, and if the set of particles is a body it is required that the measure m(χ^-1(.)), where χ is a configuration, should be absolutely continuous with respect to Lebesgue measure.