This question is in relation to the following YouTube video:
https://www.youtube.com/watch?v=jiAhiu6UqXQ
In it, an electrical generator is shown consisting of a CPU fan with thin magnets attached to the fan blades. Allegedly, bringing another magnet close to the fan causes the fan to spin. The fan's motor is utilized as a generator to power a light-bulb.
Just to be clear, I know there's no such thing as "free energy". But I'm puzzled as to why the CPU fan rotates at all. It seems intuitively that the most you could accomplish by approaching another magnet to the fan is to set up an oscillating motion (rather than continuous rotation).
Several ways of "cheating" come to mind: A magnetic stirrer hidden under the table? But, in part of the video, the demonstrator holds the fan somewhat above the table. A small battery hidden somewhere on the fan? We don't get to see it from all sides, but it doesn't look like he's flipping a switch.
Some of the comments on the video speculate that the energy comes from demagnetizing the magnets, but this seems dubious. If the device "works" to any extent it seems the input energy would be in the form of work performed by the person moving the magnet. But can the fan be started spinning by motion of the magnet alone?
