Flywheels

Part of speech: noun

Definitions

1. A mechanical device that stores rotational energy, typically used to smooth out fluctuations in energy supply or maintain speed in engines
2. A cylindrical mass that rotates to store kinetic energy, often employed in machinery to provide consistent power delivery or stabilize motion
3. A revolving wheel designed to accumulate and release energy, commonly found in various mechanical systems to enhance operational efficiency and reduce speed variations

Etymology: "Flywheels" is the plural of "flywheel," and the word is a compound of "fly" and "wheel" that describes what the device does. The "fly" here is not the insect or the verb to take flight but an older sense of "fly" meaning something that moves quickly or swiftly, as in the "fly" of a flying shuttle or a fly-boat. A flywheel is a heavy wheel that, once set spinning, keeps turning and carries its momentum, so it evens out jerks and surges in motion. The word is recorded in English from the 1600s, and it was used in the sense of a heavy wheel regulating machinery long before anyone thought of it as a store of energy. Early steam engines and clockwork relied on such wheels to keep their motion steady between the uneven strokes of a piston or the release of a spring. The energy-storage meaning in the definition you gave is the same principle applied more deliberately, which is why modern flywheels appear in vehicles, power grids and laboratory equipment.