fan changes rotation ? why?

[korialz]

earlier i placed my hand behind my case specifically on the fan part( covering it partially) just to feel the air..then i noticed that the fan starts to slow down briefly then it start up again but it is rotating on the other way(left) but when i removed my hand it slowed down briefly again and goes back the normal way(right) it rotates...this is really not a problem,im just curious as why it is happening.
the fan btw is just a preinstalled one on my corsair spec 3 so i dont know what it is..and if you're wondering how i could see the fan eventhough im covering it, im looking right through the holes at the top of the case(where another fans could be placed) and there are leds inside so its illuminated....

 

[PsyKhiqZero]

In order to change directions the fans would have to come to a stop. Are you sure what your seeing isn't an opitical illusion?

 

[photonboy]

Assuming it actually IS changing direction it may have to do with minimizing dust build-up.

I've seen this with graphics cards.

To confirm air flow you can use a piece of paper. It will either blow the paper away or suck it in.

(I agree it may be an optical illusion. Any rotating object can look like it's changing direction at specific frequencies due to how our brains sample the image)

 

[korialz]

its definitely changing direction..this time im just looking at the shadows...

 

[PsyKhiqZero]

Does the fan stop? It would be impossible for it to actually change directions without first comming to a stop. If it doesn't then your seeing an illusion.

Normal case fans do not have the dust removal feature gpu fans have. Also they are only designed to spin one way. They produce much less air when spun in the wrong direction.

 

[korialz]

fans slows down (almost into a complete stop) during the transition(placing/removing of hands)..and i just notice that it will just slow down(almost into a complete stop) if i just cover half of it but it will start to rotate the other way if im covering almost all of it.

 

[Bearmann]

Does the fan stop? It would be impossible for it to actually change directions without first comming to a stop. If it doesn't then your seeing an illusion.

Normal case fans do not have the dust removal feature gpu fans have. Also they are only designed to spin one way. They produce much less air when spun in the wrong direction.

This ^

It's an optical illusion.

 

[korialz]

uploaded a video so you guys could decide...sorry i forgot to turn the phone sideways while recording and sorry for the quality..btw im just doing this due to curiosity and atm im bored.

https://youtu.be/CqBM0gLEuZI - btw starting at 0:33 ,im just covering only half of it thats why it only slows down