Have you ever looked inside a grandfather clock or a small mechanical alarm clock, seen all the gears and springs and thought, "Wow -- that's complicated!"? While clocks normally are fairly complicated, they do not have to be confusing or mysterious. In fact, as you learn how a clock works, you can see how clock designers faced and solved a number of interesting problems to create accurate timekeeping devices. We'll help you understand what makes clocks tick, so the next time you look inside one you can make sense of what's happening!

Pendulum clocks have been used to keep time since 1656, and they have not changed dramatically since then. Pendulum clocks were the first clocks made to have any sort of accuracy. When you look at a pendulum clock from the outside, you notice several different parts that are important to the mechanism of all pendulum clocks:

There is the face of the clock, with its hour and minute hand (and sometimes even a "moon phase" dial!). There are one or more weights (or, if the clock is more modern, a keyhole used to wind a spring inside the clock -- we will stick with weight-driven clocks in this article). And of course there is the pendulum itself. In most wall clocks that use a pendulum, the pendulum swings once per second. In small cuckoo clocks the pendulum might swing twice a second. In large grandfather clocks, the pendulum swings once every two seconds.