What is the primary purpose of a flywheel in a mechanical system?

The primary purpose of a flywheel in a mechanical system is to store rotational energy and maintain speed. A flywheel achieves this by utilizing its mass and rotational inertia. When energy is supplied to the flywheel, it accelerates, storing kinetic energy in the form of rotational motion. This stored energy can later be released when there is a demand for power, thereby providing a smoother and more stable source of rotational energy to the system. As the load on the engine or motor fluctuates, the flywheel helps to maintain a consistent speed by compensating for these variations. This function is critical in applications such as engines, generators, and various machinery where stable operation is key to performance and efficiency.

Additionally, while other options might describe different components or functions within mechanical systems, they do not capture the essential role of a flywheel as effectively as the correct answer does. For example, reducing vibration or serving as a brake may involve distinct parts or mechanisms designed specifically for those purposes, while increasing torque typically pertains to gearing systems rather than the inherent function of a flywheel.