Pendulum — Junghans pendulum wall clock.jpg — Junghans pendulum wall clock.jpg — Megatherium · CC BY-SA 4.0 · source

Component

Pendulum

Also known as: Pendel · Balancier (pendule)

How it works

A weight (the bob) on a rod swings under gravity. For small arcs its period depends almost entirely on its length: T = 2π√(L/g). A pendulum of about 0.994 m beats once per second — the 'seconds pendulum' of the longcase clock.

Why it was invented

It gave clocks a natural, stable period for the first time, reducing errors from perhaps a quarter of an hour to well under a minute per day.

Invented: 1656 (first pendulum clock)
Credited to: Christiaan Huygens
Historical period: Early Modern Horology
Seconds pendulum length: ≈ 0.994 m (at g = 9.81 m/s²)
Circular error: Period lengthens slightly with larger arcs
Temperature: A steel rod changes rate by roughly 0.5 s/day per °C

Experiment in the Simulation Lab →

History and development

Galileo studied the near-isochronism of the pendulum from the early 1600s and designed, but did not complete, a pendulum clock. Christiaan Huygens built the first in 1656; Salomon Coster of The Hague made clocks to his design under a privilege of 1657. Huygens also showed that a truly isochronous pendulum must swing in a cycloid.

Within a decade pendulums were fitted throughout Europe, often by converting older foliot clocks. Later refinements — the anchor and deadbeat escapements, temperature-compensated rods (mercury, gridiron, Invar) and the free pendulum — made the pendulum clock the world's most accurate timekeeper until quartz in the 1930s.