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Columbia University Press
wheel and axle
simple machine consisting of a wheel mounted rigidly upon an axle or drum of smaller diameter, the wheel and the axle having the same axis. It is fundamentally a form of lever, the center common to both the wheel and the axle corresponding to the fulcrum, the radii of the two parts to the arms. The effort (applied to the wheel) needed to overcome the resistance (acting upon the axle) is relatively small. The mechanical advantage gained by the use of the wheel is equal to the ratio of the radius of the wheel to the radius of the axle. The wheel and axle is not as efficient as the lever, since a part of the effort must be used to overcome the resistance of friction. In common use, a crank or handle often takes the place of the wheel. Applications of the wheel and axle are numerous in everyday life; examples are the steering wheel of an automobile, the doorknob, and the windlass. The effort is applied through a greater distance than is the resistance, but this effort is applied conveniently in a circle. In the treadmill, the windmill, and the waterwheel, the wheel and axle led the way to the utilization of power in modern machinery. Clockmakers were pioneers in devising ways of transmitting and controlling power by the use of the wheel and axle.