system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : I don’t know what to refer to it as, maybe a phenomenon, but if you look at something spinning like a fast fan and it looks like it slows down and goes in the opposite direction, despite obviously not doing so?
gpt
This is a phenomenon called 'aliasing'. It happens when your brain can't keep track of which blade on the fan is which, or how far it had spun since your last perception of it. It also happens in film, when you would see spokes on wheels, or rotors on aircraft seem to spin at a much slower speed, or even backwards. In this case, it's due to the frame rate of the camera being close to some factor of the rpm of the wheel multiplied by the number of spokes.