Pythagorean Cup or the GreedyCup, credited to Pythagorus of Samos, ancient Greece.
This is a unique which looks mostly like a normal cup, with a raised tube in the middle. It works on the simple principle of air pressure & hydrostatic pressure.
Above is a cross section view I the cup & it's functioning.
Between step C & D, the pouring out of water creates a hydrostatic pressure which leads from C to D, instead of B.
Photo courtesy : Wikipedia
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