![]() ![]() Most large tuning forks are made of hard aluminum alloys, but quartz is an even better choice. The best tuning forks are made of hard, brittle materials with little internal friction to slow their motions. The fork continues to vibrate until internal friction and air resistance finally bring it to a stop. This repetitive motion occurs because, while internal forces keep trying to restore the fork to its original shape, inertia keeps causing it to overshoot that destination. When something bends these tines out of place, the entire fork vibrates for a long time as the tines swing back and forth about their original positions. A tuning fork resembles the salad variety except that it has only two tines protruding from a short handle. This precise behavior is why tuning forks are the pitch standards for orchestras and why their vibrations are so useful for building accurate clocks. Whether a tuning fork vibrates a little or a lot, its pitch is always the same, determined only by its mass and the "stiffness" of the restoring force that acts when the object is moved out of its rest, or equilibrium, position. Similarly, the pendulum's period does not depend on the size of the arc through which it swings but only on its length and, of course, gravity. Because it's a harmonic oscillator, like the pendulum of a traditional clock, the tuning fork completes one full back-and-forth cycle of motion in a time interval or "period" that doesn't depend on the overall extent of that motion. Cut in the shape of a tiny translucent tuning fork, this quartz timekeeper is what gives the clock its exquisite accuracy. ![]() ![]() Something is moving back and forth inside the quartz clock and, like the pendulum or balance wheel of a so-called "mechanical" timepiece, that something has the steady beat of a harmonic oscillator. They appear to have no moving parts and thus nothing in common with earlier mechanical clocks. Beyond that observation, quartz clocks are rather mysterious. After all, quartz isn't visible outside the clock so it must be doing something inside. It should come as no surprise that the heart of a modern quartz clock is a tiny piece of quartz. ![]()
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