Friction Wheel
in machinery, a wheel, the motion of which is caused by the friction of a moving body, or, conversely, which communicates motion to a body by frictional contact. In one variety, one wheel being driven becomes a motor to the other, their perimeters being in contact. The surface is usually clothed with leather, rubber, or some sufficiently elastic material which does not polish too readily, and thus induce slipping. By grooving the perimeters of the wheels, the contact may be made more intimate, as the surface engaged is increased, and the elastic material of the respective faces caused to bind. In another form a collar fastened to the central shaft has four pivoted arms. When the rim turns in one direction, the arms turn on their pivots, leaving the rim and failing to transfer the motion to the shaft. When the rim turns in the contrary direction, the arms catch against it and are rotated by the contact, turning the shaft also. Another form has an upper india-rubber wheel with Vedge, clamped between two metallic plates. By screwing up the nut which holds the parts together, the disk is made to expand radially, and thus increase the tractive power on the lower driving wheel. The term friction wheel is often, but erroneously, applied to wheels which diminish friction; these are properly called anti-friction wheels.
FRIENDLY ISLANDS. See TONGA.