Which statement best defines a flywheel?

• A. A device that stores electrical energy
• B. A device that absorbs torsional vibrations of the crankshaft
• C. Limits the speed changes during sudden load changes
• D. Transmits motion to the cam

Answer: (C)

A flywheel is all about inertia: a heavy rotating mass on the crankshaft resists changes in rotational speed. Its main role is to smooth out engine torque by storing kinetic energy when load increases and releasing it when load drops, which limits speed changes during sudden load changes. That makes the statement about limiting speed changes the best definition. It does store energy, but as rotational kinetic energy, not electrical energy, so storing electrical energy isn’t the right description. It can help damp torsional vibrations, which is related to its effect on the crankshaft, but the primary purpose described here is smoothing speed changes. It doesn’t directly transmit motion to the cam; timing to the cam comes from the timing gear or belt connected to the crankshaft.