A weather vane could be considered a simple form of kinetic sculpture.
Kinetic sculpture is a branch of 3-D art in which parts of the sculpture move. The motion may be driven by a built-in motor, viewers, gravity or other environmental forces. The parts of a kinetic sculpture that can move are called "motion elements." They may be arranged to vary the way light interacts with the sculpture, alter its overall shape or simply move in an aesthetically pleasing way.
Wind-Driven
Kinetic sculptures driven by wind require no power source or human interaction. They also have the advantage of unpredictable movement and harmony with natural forces. By harnessing wind energy in aesthetically pleasing ways, these kinetic sculptures can draw viewers' attention to the natural environment surrounding them. Simple wind-powered sculptures include weather vanes and wind chimes. More complex examples could be large outdoor installations that have screw-shaped wind catchers, sails or pendulums or sculptures that combine wind-powered motion elements with interactive or motorized elements.
Interactive
Interactive kinetic sculptures depend on the artist or viewers to move their parts. Marcel Duchamp's "Bicycle Wheel," an early example of interactive kinetic sculpture, consists of a bicycle wheel mounted upside down on a kitchen stool; a viewer can spin the wheel and watch it whirl. Interactive kinetic sculptures may simply have hanging or axle-mounted motion elements that a viewer can push to launch a motion. More complex sculptures may have interactive clockwork, weighted mechanisms to multiply a viewer's simple action or pieces the viewer can move around and reattach in new configurations.
Motorized
Some kinetic sculptures have motion elements driven by a built-in motor. The motor may either keep a mobile turning or steadily alter the configuration of a sculpture's parts. In some cases, the entire sculpture works as a motorized vehicle. The Kinetic Grand Championship of Humboldt County, California is the first of many kinetic sculpture races held around the world. Contestants build amphibious kinetic sculptures and race them through various terrains over three days.
Gravity-Powered
Gravity-powered kinetic sculptures could be considered a subset of the interactive type, since they cannot run indefinitely powered by gravity alone. However, some sculptures rely on human interaction only for an occasional reset, then run independently for some time. Examples include sculptures in which balls run down a long track, possibly setting off other motion elements as they pass. Pendulum-powered sculptures also fall into this class, as do sculptures in which one or more counterweights set off the motion. Even grandfather clocks could be considered a specialized form of gravity-powered kinetic sculpture.
