Radiometer

You may have seen radiometers before, spinning away in some kitchy ornament. Having a simple, 'Classic' one around is kinda cool. Place it near light and watch the 'windmill' start to spin. Put it in direct sunlight and it'll spin so fast you'll hear it creaking.

A cool toy, and I've found when ...moreI place it near my window, I can use it to tell the time, based on the speed of rotation and the angle of the sun in the sky.

Not really, but it is fun to watch. If you can find one with a glass base (instead of the black ) they are much more aesthetically pleasing.