  We argue that certain materials exhibit asymmetry of their mechanical and
conducting properties with respect to clockwise/counterclockwise rotation. We
show that a cylinder made of a suitably chosen semiconductor coated in a
metallic film and placed in the magnetic-field background can serve as a
"rotational diode" which conducts electricity only at a specific range of
angular frequencies. The critical angular frequency and the direction of
rotation can be tuned with the magnetic field's strength. Mechanically, the
rotational diode possesses different moments of inertia when rotated in
clockwise and counterclockwise directions. These effects emerge as a
particularity of the Fermi-Dirac statistics of electrons in rotating
conductors.
