How Does a Cuckoo Clock Work?

"Gravity" is the simple answer to the title question of this article. But of course it's really not that simple. A traditional cuckoo clock is mechanical, and operates via weights, a pendulum, and a set of geared wheels. In cuckoo clocks, a pair of bellows and whistles is connected to this timekeeping system, and there's usually also cuckoo clock movements that play music or cause carved figures to perform a set of actions every hour or half-hour. Here's how it all comes together.

How Cuckoo Clocks Keep Time
It's the pendulum that keeps time in a cuckoo clock. For this we have Galileo to thank, for he was the one who discovered that the rate of a pendulum's swing is essentially constant. This discovery was applied to timekeeping in 1656 when the Dutch astronomer Christian Huygens created the first pendulum clock.

However, a cuckoo clock still needs a power source, and that's where the weights come in. With cuckoo clocks, the weights are typically shaped like pine cones and hung on chains. The chains are hung from the geared wheels, which are connected to one another. The wheels drive the timekeeping mechanisms as the weights slowly move closer to the ground. How soon it takes the weights to run down depends on whether your cuckoo clock movement is a one-day movement or eight-day movement.

How Cuckoo Clocks Make Noise
Legend has it that the device that makes the cuckoo sound was inspired by the bellows and pipes of a church organ. The cuckoo clock movement drives air into and out of a pair of bellows. As the air exits each bellow, it passes through a corresponding slotted whistle. One makes the "cu" sound, the other makes the "ckoo" sound.

Traditional cuckoo clocks have either two or three weights. If two, the cuckoo will call the hour and half-hour without music. If there are three weights, music will follow the cuckoo's call every hour, and with some clocks, every half-hour. The number of notes or songs that its music box can play is one factor in the price of a cuckoo clock. On most clocks, a gong will accompany the cuckoo.

How Battery-Powered Cuckoo Clocks Work
If you opt for a battery-powered cuckoo clock, your clock will play a recording of a cuckoo rather than creating a cuckoo sound via air, bellows, and whistles. With battery-powered cuckoo clocks, the weights are merely decorative.