Page "Continuum mechanics" Paragraph 1

Modeling an object as a continuum assumes that the substance of the object completely fills the space it occupies.

Modeling objects in this way ignores the fact that matter is made of atoms, and so is not continuous ; however, on length scales much greater than that of inter-atomic distances, such models are highly accurate.

Fundamental physical laws such as the conservation of mass, the conservation of momentum, and the conservation of energy may be applied to such models to derive differential equations describing the behavior of such objects, and some information about the particular material studied is added through a constitutive relation.