Crookes radiometer

The Crookes radiometer, commonly known as a solar windmill, is a partially vacuum airtight glass bulb with a set of metal blades inside, with one side black and the other white. When there is light shining, compared to the white surface with weak heat radiation absorption ability, the black surface absorbs more heat radiation and the air temperature is higher. However, the air temperature near the white surface is lower, and the temperature difference causes air flow. The blades are subjected to the force of air molecules, so the impeller always rotates in a black to white direction, and the stronger the light, the faster the rotation.

The unit is designed for unsupervised public use: controls are recessed or shielded, moving parts are enclosed, and the interface is operable by a child of about six with no instruction. Where a screen is used, the language can be switched without changing the hardware, and the content can be replaced on site.