system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do wheels appear to be turning backwards at certain speeds?
gpt
This is caused by sampling their position at certain frequencies. For instance, if the wheel revolved 30 times per second but you sample it 31 times per second, each time you see it it will have *nearly* reached its starting point. When you join up those images, it appears to be moving backwards. Slight differences could cause other similar effects, such as the wheel appearing to rotate slowly.

Because this is a sampling rate effect, it can be seen any time there is such a sampling bias. Most obviously, film recordings sample at a set framerate, which is why you can see it in TV programs. Your eyes are not really susceptible on their own because they don't have a framerate in the same way, but environmental factors such as flourescent lights (which flicker very quickly) can still cause you to see a series of samples.