Atomic scale engines: Cars and wheels

We introduce a new approach to build microscopic engines on the atomic scal e that move translationally or rotationally and can perform useful function s such as the pulling of a cargo. Characteristic of these engines is the po ssibility to determine dynamically the directionality of the motion. The ap proach is based on the transformation of the fed energy to directed motion through a dynamical competition between the intrinsic lengths of the moving object and the supporting carrier.