The flywheel is a heavy wheel attached to the shaft of an engine to keep its speed nearly constant. It is used where the forces driving the engine shaft are not constant.

The driving forces in a gasoline engine come from a series of explosions in the engine cylinder. The driving forces produce the power needed by the engines load.

Sometimes the driving forces become momentarily larger than neccessary for the engines load, and the engine speed increases. Then the flywheel absorbs the excess energy and prevents the speed from increasing rapidly.

At other times, the driving force from the cylinder become momentarily smaller than necessary. Then the flywheels "inertia" keeps the speed from decreasing rapidly. The action of a flywheel decreases as the number of cylinders of a gas powered engine increases.

For example, less of the engine cycle energy must be temporarily with a 2 clylinder engine than with a 3 cylinder engine.

Chris--hope this helps a little.