ABSTRACT
There exists a large class of fluid flows in which the motion is caused by buoyancy in the fluid. Buoyancy is the force experienced in a fluid due to a variation ofdensity in the presence ofa gravitational field. According to the definition ofan incompressible fluid, as was presented in Sec. 1.6, variations in the density normally mean that the fluid is compressible, rather than incompressible. That being the case, one might expect that the material content ofthis chapter would be presented in Part IVofthe text, rather than Part III. The rationale for this apparent contradiction is discussed below.
