# flywheel

/ˈfɫaɪˌwiɫ/ (US) · /flˈaɪwiːl/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/flywheel
Updated: 2026-05-28

## Definition

a heavy wheel that spins inside a machine to keep it moving smoothly. It stores energy so the machine doesn't stop when the power goes out.

For teachers: a mechanical device used to store rotational energy and provide a smooth, continuous output of power. It consists of a heavy wheel with a large moment of inertia, designed to maintain momentum during fluctuations in the power source.

## Examples

- The flywheel helps the engine run more smoothly.
- In a steam engine, the flywheel ensures that the pistons continue moving even when the pressure drops between cycles.
- Modern hybrid vehicles often use a flywheel to capture kinetic energy during braking, which is then released to assist the engine during acceleration, improving overall fuel efficiency.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.