Enrico Fermi. (Library of Congress)

Flywheels store kinetic energy (energy of motion) by mechanically confining motion of a mass to a circular trajectory. The functional elements of the flywheel are the mass storing the energy, the mechanism supporting the rotating assembly, and the means through which energy is deposited in the flywheel or retrieved from it.

Energy can be stored in rings, disks, or discrete weights, with spokes or hubs connecting the storage elements to shafts, and bearings supporting the assembly and allowing it to rotate. Energy may be transferred into or out of the wheel mechanically, hydraulically, aerodynamically, or electrically.

History

Ubiquitous in rotating machinery, flywheels have been used as a component of manufacturing equipment since their application in potters' wheels before 2000 B.C.E.

Flywheels attained broad use during the Industrial Revolution. In the embodiment of this era, flywheels used heavy rims built from cast iron...