The introduction of gas bubbles into a liquid might be expected to cause a relatively large floating body to sink when the average density of the fluid is less than the average density of the body. However, the rising bubbles could entrain the liquid, which would produce an upward drag on the body and thus lower the fluid density required to sink the body. Due to this drag, it is in fact not clear whether any amount of bubbles can cause a floating body to sink. In addition, there are many other effects that could alter the requisite fluid density. We describe qualitative lecture demonstrations which show that bubbles can indeed sink a body, including the case of ice in water. We also describe a quantitative experiment to determine the density of bubbly water required to sink a spherical body. The specific gravity of this body is varied from 0.99 to 0.75, and the results are compared to a simple theory.

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Richard D.
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Role of Naturally Occurring Gas Hydrates in Sediment Transport
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Regent Pet Products, Moorpark CA (805-529-111, Part No. PL-T714. These bubblers are commonly available in pet stores.
Penn-Plax, Inc., Garden City, NY (800-228-3850, Part No. VT-412. Adjustable aquarium manifolds are commonly available in pet stores.
Sierra Instruments, Monterey, CA (800-866-0200, Part No. 826 with digital display.
Cole-Parmer Instrument Company, Vernon Hills, IL (800-323-4340, Part No. U-32460-46 (1–10 l/min).
BSI Adhesives, Atascadero, CA (831-466-1717,, Part No. IC-2000.
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