Gears and pulleys are used for many common objects and machines. A gear is "a toothed machine part, such as a wheel or cylinder, that meshes with another toothed part to transmit motion or to change speed or direction." A pulley is "a wheel with a grooved rim in which a rope, chain, or belt can run in order to change the direction or point of application of a force applied to the rope" (Reference 1).
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Gears can make things move in different directions, more quickly or slowly. Examples of common objects with gears are non-digital clocks, vehicles, drills, manual can openers and bicycles. Another use for gears is to "expand the physical limits of the human body." Powered wheel chairs and lifts have gears. These devices allow the elderly, handicapped and others to achieve physical feats they normally can't.
Types of Gears
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Spur Gears are usually used for "slow speeds." Examples are winches, windup clocks, and washing machines. Bevel Gears are used for objects that reach higher speeds, such as certain automobiles and hand drills. Worm Gears are often used in conveyor systems to lock the gears. Locking occurs because "the worm can easily turn the gear, but the gear cannot turn the worm." Helical gears are similar to spur gears but rotate more quietly and smoothly. These gears are used in "almost all car transmissions."
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Pulleys can be fixed, movable or both. If a pulley is fixed it is "attached in a position above a load to be lifted." If a pulley is movable it is "attached to a load that is being lifted." These two types can be combined to create a more complex pulley system. Examples of common pulley systems can be found on flagpoles, blinds, elevators, sailboat rigging, cranes, tow trucks, clothes lines and garage doors.
- "What Do Gears and Pulleys Do?"; David Glover; 1996