THE CHAOTIC MOTION OF DISKS sinking in a fluid can be mapped onto a diagram whose parameters reflect the density and viscosity of the fluid and the size and density of the disk. A Colorado State/Michigan collaboration has discovered that the disk trajectories (videotaped and anatomized into numerical coordinates) are of four types: steady falling, tumbling, periodic oscillating, and an unpredictable chaotic mode. (Stuart Field et al., Nature, 17 July 1997; more details at University of Michigan website.)

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