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Elements such as bearings, couplings, clutches, brakes, belts and chains are examples of components that facilitate movement.
Bearings and couplings evolved from the wheel and axle while belts and chains are derived from the concept of the pulley.
Many of the more complex mechanisms we use today have their roots in these simpler devices.
The ratchet and pawl is an example: it combines elements of a lever, a spring and a gear to create a device that allows rotation or movement in only one direction.
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