How things work
How a clock keeps time
A weight-driven pendulum clock with its case and dial taken off. Every wheel has its real tooth count, and the escape wheel moves only when the pallets let it.
The clock
Look closer
What is simplified
- The pallets are cut for a swing of about 4 degrees each side so you can see the anchor move. A real deadbeat clock of this kind swings only 1 to 2 degrees each side.
- The dial, the case, the gears that drive the hour hand, and the ratchet that lets you wind the weight are left out. The plates are open frames so you can see between them; many real plates are solid.
- The length slider moves the bob much further than a real clock allows. The real adjustment is a nut under the bob that moves it by fractions of a millimeter.
- The rate is worked out for an ideal pendulum with all its weight at the center of the bob. A real rod has weight of its own, so a real seconds pendulum is slightly longer overall.
- With the anchor out, the wheels are shown turning far slower than a real train would run away, so that you can follow them. The pendulum also dies away sooner than a real one.
- Starting the pendulum here builds the swing up on its own. A real one needs a push by hand.
In short
A mechanical pendulum clock is driven by a falling weight or a wound spring that pulls on a train of gears. Left alone, the gears would spin freely. An escapement stops that. An anchor with two pallets rocks with the pendulum and lets the toothed escape wheel advance only one tooth per swing. Each release also gives the pendulum a small push to keep it swinging. The pendulum's length, not the escapement, mainly sets how fast the clock runs.