A mechanical clock is defined as a clock with moving mechanical parts. It was the first completely self-sustaining clock, as opposed to water clocks, sundials, and hour glasses. Mechanical clocks are still very popular, particularly in forms such as grandfather clocks and cuckoo clocks. While mechanical clocks have many moving parts, these parts fall into only a few categories.
The Face
The part of the clock that everyone sees, the face of the clock consists of the actual face, which is typically a disc displaying numbers, as well as the hands of the clock. The hands may be as few as two, one for hours and one for minutes, but may have more to denote seconds, and even date.
Pendulum
After the face, the pendulum is the second most prominent part of a clock. While many modern electrical clocks still have a pendulum for show, the pendulum is what keeps time for a mechanical clock. As the pendulum swings back and forth, it drives the hands of the clock forward, second by second, which add up to minutes.
Cogs
The pendulum drives a series of cogs that operate the various hands of the clock. If there is a second hand, it is driven directly by the pendulum. A series of cogs continues to turn with every stroke of the pendulum, but these are turned into smaller movements to drive the slower minute and hour hands.
Weight
All true mechanical clocks, as opposed to modern incarnations, are also driven by a weight or series of weights. This weight hangs from the main cog that drives the minute and hour hands and it places a constant pull on the cogs of the clock to add momentum to the movement. These must be periodically adjusted to keep a clock from losing time.
