Starting from this chapter and to the end of the first part we are building a
closed system of equations of a fluid model. Firstly, we discuss differential
conservation laws, and related balance equations. All previously obtained expressions
are applied then to the mass of a body, and this gives the first equation of the fluid
model, the continuity equation.
Keywords: Balance equation, Compressibility, Continuity equation, Differential
conservation law, Flow through a surface, Flux, Levi-Civita symbol, Mass flux
density, Rate of volume expansion.
