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...

Sprinkler Image Gallery

­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!­

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