The present invention provides a new family of ultrasonically powered medical devices and systems for powering such devices. Disclosed are methods for improving the overall power transfer efficiency of devices according to the present invention, as well as a wide variety of medical uses for such devices and systems. Devices of the present invention comprise a transducer that, during operation, converts electrical energy into high frequency, low amplitude mechanical vibrations that are transmitted to a driven-member, such as a wheel, that produces macroscopic rotary or linear output mechanical motions. Such motions may be further converted and modified by mechanical means to produce desirable output force and speed characteristics that are transmitted to at least one end-effector that performs useful mechanical work on soft tissue, bone, teeth and the like. Power systems of the present invention comprise one or more such handheld devices electrically connected to a power generator. Examples of powered medical tools enabled by the present invention include, but are not limited to, linear or circular staplers or cutters, biopsy instruments, suturing instruments, medical and dental drills, tissue compactors, tissue and bone debriders, clip appliers, grippers, extractors, and various types of orthopedic instruments. Devices of the present invention may be partly or wholly reusable, partly or wholly disposable, and may operate in forward or reverse directions, as well as combinations of the foregoing. The devices and systems of the present invention provide a safe, effective, and economically viable alternative source for mechanical energy, which is superior to AC or DC (battery) powered motors, compressed air or compressed gas, and hand powered systems.