The Black White thing is a Crookes Radiometer[1] and it rotates because of differential heating of the black and white sides of the plates interacting with air molecules to create a tiny air flow from the light side to the dark side of the plate.

The device is under _partial_ vacuum. Under total vacuum, no rotation will occur, if the air pressure is too high, drag forces outpace the tiny thrust.

https://en.wikipedia.org/wiki/Crookes_radiometer