Fan - blades movement

[murulidhara]

This is question regarding vision ( illusion)

When we swith on a table fan we see in the begining clockwise and anticlockwise movenents. Why is it so? Is it due to persistance of vision? And alo at very high speed we can see the other side as if nothing is there?

[Rocket Man]

the eye works at a reasonably fixed refresh rate, around 16 frames per second (take it as shutter speed on a camera, we see motion blur too)

 

as the fan starts up, the eye sees the fan blade go around and around. but when you get up to higher speeds, the motion blur starts to overlap in funky ways such that you see a generalised motion slow to a stop and start moving backward. the blades aren't clear but the eye filters down to an illusion of motion.

you'll see this with pretty much any camera, however, depending on the shutter speed and delay between frames, the images can be quite clear.

[murulidhara]

is it the same phenomenon as persistance of vision which is the case of motion pictures?

 

Murulidhara

[insane_alien]

yeah, same effect. different application.