Torsional locomotion

One edge of an elastic rod is inserted into a friction-less and fitting socket head, whereas the otheredge is subjected to a torque, generating a uniformtwisting moment. It is theoretically shown andexperimentally proved that, although perfectlysmooth, the constraint realizes an expulsive axialforce on the elastic rod, which amount is independentof the shape of the socket head. The axial forceexplains why screwdrivers at high torque havethe tendency to disengage from screw heads anddemonstrates torsional locomotion along a perfectlysmooth channel. This new type of locomotion findsdirect evidence in the realization of a ‘torsional gun’,capable of transforming torque into propulsive force.