the bulk viscosity (also called volume viscosity) expresses a type of internal friction that resists the shearless compression or expansion of a fluid. knowledge of formula_28 is frequently not necessary in fluid dynamics problems. for example, an incompressible fluid satisfies formula_33 and so the term containing formula_28 drops out. moreover, formula_28 is often assumed to be negligible for gases since it is formula_2 in a monoatomic ideal gas. one situation in which formula_28 can be important is the calculation of energy loss in sound and shock waves, described by stokes' law of sound attenuation, since these phenomena involve rapid expansions and compressions.