A small toy that rotates over a teacup filled with hot water.

this is actually a small Stirling engine (Stirling engine), a power plant driven by temperature difference and gas expansion and contraction. Robert Stirling invented it in 1816 and has a long history. The structure design of this Stirling engine on the coffee cup is relatively simple. The following is a schematic diagram:

the green piston on the upper right can slide up and down, but it cannot leak. A cylinder of gas in a cylindrical container is

enclosed in the cylinder. With the heating below, the volume of the gas expands and the piston is pushed up to drive the connecting rod on the right and drive the disc to rotate.

while the yellow part is not a completely airtight piston, the gas can leak through the next gap. This yellow thing is mainly responsible for controlling whether the gas is mainly heated by the heat source below (hot water in the teacup here) or cooled mainly by the cold source above (room temperature air here). As the piston pushes the right connecting rod, the left connecting rod also drives the yellow disc up and down, thus causing the air in the cylinder to circulate between heating expansion and cooling contraction, thus maintaining the movement of the piston.

there is also a version of the mini Stirling engine that requires a smaller temperature difference, which is enough to keep it turning as long as it is held in the hand.

this small Stirling engine has no practical value, but it is still fun to watch it turn on the teacup. (: mini "∠) _

PS: don't ask me where to buy this, ask Amazon in the United States.

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