Alexander Calder, Mobile, 1941, 60 x 152 3/8in., Painted aluminum, steel, steel rod, and wire, The Metropolitan Museum of Art, New York, Photo courtesy of The Metropolitan Museum of Art
Kinetic art is art that moves, and therefore optimally it engages a viewer.
One of the early artists to make kinetic art was Alexander Calder, who created mobiles that were so carefully balanced that the slightest movement of air created by an approaching viewer could set them in motion.