Answer 1:
All clocks need some part of them that perform
a regular action that takes a very predictable
amount of time. Some clocks have springs and gears
that perform this tasks, and a lot of clocks have
quartz crytals.
A pendulum clock uses a weight swinging back
and forth to provided a regular action which can
drive the rest of the clock. The reason a
pendulum works well for this has to do with the
physics of how a pendulum swings. More
specifically, the amount of time it takes for a
pendulum to complete one full swing does not
depend at all on it's mass, or the amplitude of
its swing, but only on the length of the pendulum
and gravity. Since gravity is pretty constant
on the surface of the earth, and the length of the
pendulum doesn't change, the length of time it
takes for a pendulum to complete a full cycle is
very reliable.
Because the pendulum's frequency doesn't
depend on the height to which the pendulum rises,
this means that even if the pendulum looses energy
and swings lower and lower, it timing will remain
intact.
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