Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy; adding energy to the system correspondingly results in an increase in the speed of the flywheel.

Sentinel Waggon Works Ltd was a British company based in Shrewsbury, Shropshire that made steam-powered lorries, railway locomotives, and later, diesel engined lorries, buses and locomotives.