Question

An incomprehensible liquid flows

Answer 1

In  fluid mechanics or more generally continuum mechanics, incompressible flow(isochoric flow) refers to a flow in which the material density is constant within a fluid parcel—an infinitesimal volume that moves with the flow velocity. An equivalent statement that implies incompressibility is that the divergence of the flow velocity is zero (see the derivation below, which illustrates why these conditions are equivalent).