Check out this lovely kinetic sculpture by Dolf Perenti. The various hardwoods and high-grade plywood are combined to form a mechanism called an escapement. These are the heart and soul of clocks. I'm going to let Wikipedia explain escapements further:
An escapement is a device in mechanical watches and clocks that transfers energy to the timekeeping element (the "impulse action") and allows the number of its oscillations to be counted (the "locking action"). The impulse action transfers energy to the clock's timekeeping element (usually a pendulum or balance wheel) to replace the energy lost to friction during its cycle, to keep the timekeeper oscillating. The escapement is driven by force from a coiled spring or a suspended weight, transmitted through the timepiece's gear train. The escapement releases the tooth of a gear, which therefore changes from a "locked" state to a "drive" state until the opposite arm strikes another tooth on the gear, which locks the gear again. A clock's tick is the sound of the gear train stopping as the escapement locks. The gear train is accelerated and decelerated with each tick of the clock. This locking action of the escapement allows each cycle of the timekeeping element to be counted. During each cycle the escapement permits a gear train to advance or escape slightly. The periodic advancement results in moving the timepiece's hands forward at a steady rate. This starting and stopping accounts for most of the energy usage from the spring or weight when a clock is in good working order.
I'm not sure if the one shown here is an esoteric form of escapement or something the artist invented himself. Either way, it's beautifully made and captivating!
If you want to learn more about escapements, Laurie Penman's book Practical Clock Escapements comes highly recommended. I need to get a copy myself, actually.