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A disk-like mechanical device mediating between rotary and linear motion, widely used to transmit power, store energy (see flywheel), and to facilitate the movement of heavy objects. Wheels may be solid or spoked, flanged or unflanged, with or without tires. Most usefully, they are attached to an axle through the center. Indeed, the wheel and axle is one of the classic simple machines, exemplified in the capstan, winch, and transmission gears.

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