Bouncing with Liquids and Grains

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Bouncing a ball partially filled with a liquid can create chaotic results when the motion of the ball, fluid, and vibration plate couple. The behavior of a grain-filled ball is a bit different, though. Large grains will tend to bounce with the same frequency as the ball, even across a range of vibration conditions. A ball filled with smaller grains displays a variety of responses depending on the vibration conditions. Among these is a localized wave-like form called an oscillon which oscillates with a period different from but coupled to that of the vibration plate. All these different behaviors inside the bouncing sphere have noticeable effects on its outward motion, too. The chaotic activity of the fluid inside a bouncing ball makes it unstable, and, if not confined, it will bounce itself off the vibration platform. The grain-filled ball, on the other hand, remains bouncing on the platform even after being perturbed. This seems to be a result of the energy dissipation provided by the many inelastic collisions inside the ball as it bounces. (Video credit: F. Pacheco-Vazquez et al.)

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