escapement

Regulating mechanism of a clock connecting the wheelwork with the pendulum, allowing a tooth to escape at each vibration. Without the escapement the system would simply unwind continuously, but the escapement makes this motion periodic, controlled by the pendulum. The pendulum moves the escapement back and forth, and makes it change from a "locked" state to a "drive" state for a short period that ends when the next tooth on the gear hits the locking surface on the escapement. It is this periodic release of energy and rapid stopping that makes a clock tick.

An escapement is also found in a watch, powering and regulated by a balance wheel and hairspring instead of a pendulum.