The Sciences

The Incredible Power of Crumpled Paper

By Fenella SaundersAug 1, 2002 12:00 AM

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Take a piece of paper and crumple it into as small a ball as you can. Even if you're Mr. Universe, that ball is still going to be 75 percent air. "This stuff is so thin, how could air be holding things up?" wondered Sidney Nagel, a physicist at the University of Chicago. He and his colleagues investigated by crumpling Mylar sheets and placing them under a heavy piston, with unexpected results. Although most of the compression happened in the first few seconds, the piston kept crushing the sheets by small amounts for a long time—even three weeks later. And squeezing a tightly crushed wad down to half its volume would take 64 times as much force as a normal person can exert. "Even a weight lifter isn't 64 times stronger than you," Nagel says. Paper balls resist compression because the crumples in the paper consist of many small peaks joined by a network of ridges. To crush the ball further, each ridge has to buckle in two. But compressing the ball makes more ridges, which require more energy to break. Similar kinds of crumpling occur during many familiar events, from fender benders to earthquakes. "If you get at a physical understanding of crumpling, it should have implications in all these areas," Nagel says.

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