Inertial Reference Frames for Subsystems of Deformable Bodies

It is assumed that a certain reference frame is inertial for a system of moving and interacting bodies called a large system. In the framework of classical continuum mechanics, some necessary and sufficient conditions are obtained for the existence of a reference frame for a subsystem of this large system considered as an independent large system. The motion of such a new reference frame with respect to the old reference frame (with the accuracy up to the Galilean transformations) is specified.