Inertial reference frames for subsystems of deformable bodies

In the framework of classical continuum mechanics, for the frame of reference being inertial for a certain system of moving and interacting bodies (a large system) the necessary and sufficient conditions are formulated for the existence of an inertial frame of reference for the subsystem of the bodies considered as an independent large system. The motion of such a reference frame relative to the old reference frame (with the accuracy up to the Galilean transformations) is specified.