Kinetic Art

n.
An art form, such as an assemblage or sculpture, made up of parts designed to be set in motion by an internal mechanism or an external stimulus, such as light or air.

In kinetic art the motion may be physical or implied (as in Opt art paintings). Although kinetic art encompasses a very wide variety of overlapping techniques and styles, there are a few noticeable genres:

Mobiles and Whirligigs:
Sculptures designed to move under the influence of air currents. A popular creator of mobile sculptures was Alexander Calder. The category of 'whirligig' also includes a wide variety of simple non-wind-operated toys, usually made of wood.

Rolling-Ball and Related Gadgets:
A wide variety of kinetic sculptures use rolling balls on tracks or guideways to create movement. They usually have some sort of powered lift mechanism for raising the balls and are usually continuous in operation. Other related gadgets use wheeled objects, water, or sand operating under gravity to function.

Domino:
From easy-to-build-yourself to extreme-domino-art domino toppling is becoming more and more a kinetic art world wide subject.

One-Time Gadgets:
There are a wide variety of kinetic-art assemblages designed to operate only once. The most familiar type are Rube Goldberg Gadgets, mechanisms using an assembly of complex elements to perform an absurdly simple task. Another type is domino tumbling which has been popular for several decades. A newer type, Fortean Gadgets, designed by kinetic artist Tim Fort, expand the idea of domino tumbling to wide variety of other chain-reaction techniques such as stick bombs, herringbones, and string-a-lings.

Optical Sculptures:
Some kinetic sculptures use light to create the illusion of movement. They usually involve colored filters, mirrors, diffraction gratings, and other optical elements in motion.

Automata:
Self-operating machines which can also include robotics.

Other:
The medium of kinetic art is broader than most other art media and is very hard to categorize. There are many other forms of kinetic-art, gadgets and sculptures that use a variety of unusual techniques.