Science or sleight of hand

U-M physicist Franco Nori demonstrates the old gambler's trick of dropping a card into a hat: Hold the card vertically and it will flutter randomly and miss the hat. Hold it horizontally and it drops in. In last week's issue of Nature, Nori and co-author Stuart Field reported results of experimental and theoretical studies they conducted to determine why the trick works. Field and Nori videotaped the behavior of flat disks dropped into various liquids and identified four different patterns of motion--some steady and regular, some tumbling and chaotic--depending on the initial angle of the disk and properties of the disk and fluid.

Scientists have been fascinated by the behavior of falling objects ever since Sir Issac Newton experimented with inflated hog bladders dropped off the dome of St. Paul's Cathedral in London. According to Nori, increased understanding of how objects fall will be of interest to scientists in many fields, including meteorology, sedimentology and aerospace and naval engineering. More information on the study is available at: