ElI5: why does a rotating wheel or propeller spinning at high speed look like its spinning the other way sometimes?

Question

ElI5: why does a rotating wheel or propeller spinning at high speed look like its spinning the other way sometimes?

In: Other

Answer 1

That is usually seen on recorded images, and it is because the rotation rate of the blade, is different to the frame rate of the film. So each new image has the blade in a new position, often near the last recorded image, but rarely the same, so the image appears to show a slow, sometimes reversed rotation. When in fact it is moving a great distance between images.