Almost all rotary lawn mowers are powered by two-cycle engines, four-cycle engines or a system of electric motors. These engines are attached to a number of blades. The engines convert energy into the spinning motion of these blades, which allows them to cut grass and trim lawns in a quick and uniform manner.
According to How Stuff Works, the most common engine types for rotary lawn mowers are the two-cycle and four-cycle internal combustion engine models. Two-cycle internal combustion engines only require a single crankshaft revolution to complete a power cycle. This is because in lawn mowers, the only function of the engine is to burn gasoline and oil to power the spinning blades. By contrast, a four-cycle engine requires two crankshaft revolutions. Four-cycle engines provide a lubrication system in addition to burning fuel to create mechanical energy.
Although they are rarer, some lawn mowers function with a system of electric motors instead of the traditional internal combustion engine model. These systems vary slightly from model to model, but most of them either draw on solar power or are battery charged. As with traditional mowers, these energy sources are then converted into mechanical energy when used to spin the mower blades.