A cam is a projecting part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth oscillating motion in the lever.
The cam can be seen as a device that translates motion from circular to linear. Another common example is the camshaft of a car or automobile, which takes the rotary motion of the engine and translates it into the linear motion necessary to operate the intake and exhaust valves of the cylinders.
The opposite operation, translation of linear motion to circular motion, is done by a crank. An example is the crankshaft of a car, which takes the linear motion of the pistons and translates it into the rotary motion necessary to operate the wheels.
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