No matter how big or complicated, every rotary lawn mower needs a motor to make the blade spin fast enough to cut the blades of grass cleanly.
Most rotary lawn mowers are powered by an internal combustion engine, which runs on either two cycles or four. Two-cycle motors burn a mixture of gasoline and oil, while four-cycle motors burn gasoline and have a separate lubrication system. However, rotary lawn mowers that use electric motors powered by a cord, a rechargeable battery or even solar power are also popular.
Attached to the motor is a throttle, often mounted on the handlebar, which keeps fuel flowing to the motor. To prevent injury, the motor shuts off if the throttle is released. The throttle on some rotary lawn mowers allows adjustment of the motor's speed.
The motor turns a vertical axle that's attached to a large blade, which is usually made of a single piece of steel that lies suspended horizontally a few inches above the ground. The blade typically spins at 3,000 revolutions per minute and slices the grass as it passes over it. Blades can be either straight or curved, but it's the tip of the blade at either end that does all the cutting.
Some blades are specially designed to cut the grass clippings into tiny pieces that can be used in mulch. The deck on a mulching mower is designed to contain the clippings until the mulching blade can shred them. Whether the clippings are mulched or not, they move through the deck into a side- or rear-mounted bag that collects them, or the mower returns them to the ground.
Some mowers are called 2-in-1 mowers and can be used as mulching mowers or as bagging mowers. A 3-in-1 mower allows bagging, mulching or side-discharge of grass clippings.
If the mower is self-propelled, its motor turns a drive shaft connected to a belt or chain. That connects to a gearbox attached to an axle that spins, making the lawn mower's wheels move.
Those are the basics. Next, we'll see how the evolution of rotary lawn mowers has led to a bigger and more powerful species -- the riding mower.