Periodic movements in the fluid of a body controlled by the force of its interaction with the internal mass

Progressive motion in the fluid of a body (housing) with an internal movable mass is considered. The external resistance is proportional to the squared velocity of the body and depends on the direction of motion. The control is implemented by the force of interaction of the internal body with the housing. Motions with periodic change of the velocities are obtained an analyzed. The average speed of the motion of the system is evaluated.