On the Rotation and Translation of an Incompressible

are satisfied. In (1), S, is the stress tensor, p the density, f is the body force per unit mass, and a7 is the acceleration. In (2), V is the velocity field. Consider the plane motion in a second frame, denoted by 77, which is obtained from 7 by a three-dimensional translation and a superposed rigid rotation a> = const, normal to the plane of motion. If the translation is dependent on time only, but independent of the spatial co-ordinates, then by the principle of frame indifference [1, Sec. 19], the extra stresses in the fluid are equal in I and 77; or