How quartz clocks work

The trouble with pendulum clocks and ordinary watches is that you have to keep remembering to wind them. If you forget, they stop—and you have no idea what time it is. Another difficulty with pendulum clocks is that they depend on the force of gravity, which varies very slightly from place to place; that means a pendulum clock tells time differently at high altitudes from at sea level! Pendulums also change length as the temperature changes, expanding slightly on warm days and contracting on cold days, which makes them less accurate again.

Quartz watches solve all these problems. They are battery powered and, because they use so little electricity, the battery can often last several years before you need to replace it. They are also much more accurate than pendulum clocks. Quartz watches work in a very different way to pendulum clocks and ordinary watches. They still have gears inside them to count the seconds, minutes, and hours and sweep the hands around the clockface. But the gears are regulated by a tiny crystal of quartz instead of a swinging pendulum or a moving balance wheel. Gravity doesn't figure in the workings at all so a quartz clock tells the time just as well when you're climbing Mount Everest as it does when you're at sea.

Quartz sounds exotic—with a "q" and a "z," it's a great word to play in Scrabble—but it's actually one of the most common minerals on Earth. It's made from a chemical compound called silicon dioxide (silicon is also the stuff from which computer chips are made), and you can find it in sand and most types of rock. Perhaps the most interesting thing about quartz is that it's piezoelectric. That means if you squeeze a quartz crystal, it generates a tiny electric voltage. The opposite is also true: if you apply a voltage to a piece of quartz, it vibrates at a precise frequency (it shakes an exact number of times each second).

Inside a quartz clock or watch, the battery sends electricity to the quartz crystal through an electronic circuit. The quartz crystal oscillates (vibrates back and forth) at a precise frequency: exactly 32768 times each second. The circuit counts the number of vibrations and uses them to generate regular electric pulses, one per second. These pulses can either power an LCD display (showing the time numerically) or they can drive a small electric motor (a tiny stepping motor, in fact), turning gear wheels that spin the clock's second, minute, and hour hands.