An oscillating sprinkler like the one shown above is one of the most common sprinklers around. It sprays out a fan-shaped curtain of water, and the metal arm oscillates back and forth to cover a rectangular area perhaps 20 feet by 30 feet (6 meters by 9 meters) in size.

If you've thought about it for more than five seconds, you've probably wondered about the "oscillating" part of an oscillating sprinkler: What makes the arm go back and forth? In this edition of HowStuffWorks, you'll learn exactly how it happens!