During an ice storm, freezing rain fell on a rapidly rotating toy windmill during very windy conditions. As the water froze on the perimeter of the spinning wheel, it formed unusual icicles radiating outward from the perimeter of the wheel (Fig. 1). These centrifugal icicles are easy to understand from a conceptual standpoint — the freezing water drops are forced outward from the center by the centrifugal force, analogous to the sediment in a centrifuge tube. However, explanations from an inertial perspective prove to be very difficult, especially if one is reminded of the tendency of water drops to follow tangential trajectories when the water breaks away from a spinning wheel (see Fig. 2).
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2004
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