What is the main purpose of a flywheel on an engine or machine?

• A. To store rotational energy and smooth out power delivery
• B. To cool the engine
• C. To increase torque permanently
• D. To adjust stroke length

Answer: (A)

A flywheel stores kinetic energy in the rotating mass to smooth out the engine’s power delivery. When the engine produces bursts of power, the flywheel speeds up a little; when the load pulls more power than is being produced at that moment, the flywheel releases energy and slows down. This inertia keeps the shaft turning steadily, reduces vibrations, and helps maintain momentum between power strokes. It’s not about cooling the engine, permanently increasing torque, or changing stroke length—the flywheel’s job is to smooth and stabilize rotation. The amount of smoothing comes from how much inertia the wheel has, which depends on its mass and how that mass is distributed (more weight toward the rim means greater inertia).