This is an Euler's Disk

Euler's Disk is a scientific educational toy used to illustrate and study the dynamic system of a spinning disk on a flat surface (such as a spinning coin), and has been the subject of a number of scientific papers. The apparatus is known for a paradoxical dramatic speed-up in spin rate as the disk loses energy and approaches a stopped condition. This phenomenon is named for Leonhard Euler, who studied it in the 18th century. This particular version of this toy consists of a heavy, thick chrome-plated steel disk and a rigid, slightly concave, mirrored base.
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