In this paper, the rotary oscillation of a rigid sphere in an incompressible couple stress fluid is studied. The classical no slip boundary conditions are imposed on spherical boundary. Moreover, it is assumed that the couple stresses on the boundary of the sphere vanish. In the present study, the motion is generated by a sudden rotary oscillation of the rigid sphere about an axe passing through its center with a time-dependent angular velocity. Stokasian assumption is taken into consideration so that the non-linear terms are neglected in the equation of motion. The torque experienced by the couple stress fluid on the spherical body is obtained using an integral formula. Exact solutions are obtained and results are illustrated through graphs.
