I recently made a set of three geometrically identical cylindrical enclosures, filled with different materials, which show surprising fluid flows through small holes. TPT readers may find the set a useful demonstration tool for their classes. It is not difficult to make the set since the enclosures are made of typical clear acrylic stock and the relevant fabrication tips on similar enclosures are available.1 The enclosures, in order, contain equal volumes of water and air, ceramic microsphere (CMS) and air, and sand and air. (A drop of red food color was added to dye the water for visual clarity.) On average, the CMS grain is approximately 10 times smaller than that of the sand. Each enclosure is comprised of two equal and axially tandem tubes, a disk with a central hole placed in between the tubes, and two disks as end covers. For each enclosure, I first made one...

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