An engine requires a rotating mass to build _________ to keep it running between power pulses.

An engine requires a rotating mass to build _________ to keep it running between power pulses.

• A. Pressure
• B. Speed
• C. Friction
• D. Inertia

Answer: (D)

Rotational inertia is what keeps an engine turning between power events. The rotating mass, like a flywheel, stores kinetic energy when combustion produces torque and then releases it to carry the crankshaft through the gaps before the next power pulse. This smooths out speed fluctuations and keeps the engine running smoothly. Energy stored depends on the mass and how fast it’s spinning, described by the rotational energy formula 1/2 I ω^2. Pressure, speed, and friction don’t provide this energy storage in the same way: pressure is a force, speed is a rate, and friction would oppose motion rather than help maintain it.

Rotational inertia is what keeps an engine turning between power events. The rotating mass, like a flywheel, stores kinetic energy when combustion produces torque and then releases it to carry the crankshaft through the gaps before the next power pulse. This smooths out speed fluctuations and keeps the engine running smoothly. Energy stored depends on the mass and how fast it’s spinning, described by the rotational energy formula 1/2 I ω^2. Pressure, speed, and friction don’t provide this energy storage in the same way: pressure is a force, speed is a rate, and friction would oppose motion rather than help maintain it.