If you have a lawn, then at some point during the summer, when it gets really hot and dry, you end up pulling out the sprinkler...

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!