A mobile is a type of kinetic sculpture constructed to take advantage of the principle of equilibrium. It consists of a number of rods, from which weighted objects
or further rods hang. The objects hanging from the rods balance each other, so that the rods remain more or less horizontal.
Each rod hangs from only one string, which gives it freedom to rotate about the string.
The sculptor Alexander Calder is well known for his mobiles. Calder is credited with inventing the mobile in 1931.