Oscillations & pendulums

A swing on the playground, a plucked guitar string, the pendulum of an old clock: all around you, things are swinging back and forth. This regular back and forth is so reliable that people used it to measure time for centuries. Let's take a look at what's behind it.

What is an oscillation?

An oscillation is a motion that repeats regularly: there, back, there, back. The time for exactly one full swing, once there and back again, is called the period T. If a pendulum takes 2 seconds for one full swing, then T = 2 s. The smaller T is, the faster it swings.

Only the length matters

Pendulums follow a surprising rule: the length alone sets the pace. Whether the bob is heavy or light, whether you give it a strong or a gentle push: the period stays the same, as long as the swing does not get too wide. A longer pendulum swings more slowly, a shorter one faster. On Earth, a pendulum about 1 m long takes roughly 2 seconds for one full swing.

Pendulum clocks

Exactly this reliability made the pendulum the heart of the clock: because a pendulum of fixed length always swings at the same rate, it can push a gear wheel forward in even steps. For almost 300 years, pendulum clocks ticked as the most accurate clocks in the world. If a clock ran too fast, you simply made the pendulum a little longer.