What Makes a Crookes Radiometer Spin?

Here is more on the Crookes radiometer. Interestingly, the mechanism that causes the vanes to rotate is still disputed, with thermal transpiration around the edges of the vanes due to differential heating of the dark and light sides creating the force that causes them to rotate being the most common explanation. Can you increase the rotation speed by adding more edges?


The experimental technique in this video is sloppy. A shaky hand aiming a laser pointer at a radiometer vane is hardly a controlled experiment.

According to the Wikipedia article, the all-black radiometer modeled by researchers at UTexas confirms Einstein’s theory of how this works. Their Monte Carlo simulation was consistent with experiment.