A friend of mine asked me where the energy comes from in this setup: Imagine a fan/windmill inside a box. The fan is only allowed 2 turn clockwise and is connected to an axel which exits the box. The atmosphere will keep the air inside the box at, well, atmospheric temperateure. Every so often from random pressure changes, the pressure at 1 side of the fans blade(s) will be higher than the other. When the high pressure is on the right side of the blade it will turn the fan clockwise (its a very well lubricated fan). The result is constant, very slow, clockwise rotation. I reckon the turning motion is getting its energy from the high pressure air but it seems like its turning useless high-entropy heat energy from the air into useful low-entropy energy in the form of turning motion. A violation of the second law?