# Does a fan spinning at infinite speed move any air?

#### JimmyRott

##### Expert Member
Does it? Or does all the air just bounce off the back edge of the blades?

#### saor

##### Honorary Master
Hypothetical infinities and rigid mechanical systems gonna get confusing real quick. Why don't you just define an upper limit for the fan speed?

#### TheSlinger

##### Senior Member
It obviously moves an infinite amount of air per a second of operation.
The important question is what invert & battery setup would optimally power the fan during load-shedding?

#### Slootvreter

##### Honorary Master
Maybe it does, maybe it doesn't.

#### Pox

##### Expert Member
Not sure what speed you have to get up to, but eventually the air can't move into the space left 'behind' the moving fan blade and a vacuum will form. So no air will be pumped. It's called cavitation when in water, dunno if it's called the same in air.

#### Surv0

##### Executive Member
Not sure what speed you have to get up to, but eventually the air can't move into the space left 'behind' the moving fan blade and a vacuum will form. So no air will be pumped. It's called cavitation when in water, dunno if it's called the same in air.
No cavitation is water turning to gas. The same exists in the air caused by wingtips, but in reverse.

#### Scooby_Doo

##### Executive Member
If its infinite, then its inside a black hole.

#### JimmyRott

##### Expert Member
It obviously moves an infinite amount of air per a second of operation.
The important question is what invert & battery setup would optimally power the fan during load-shedding?
How does the air enter into the area between the blades? If you were to write an equation for the position of the blades they would be everywhere all the time. Not allowing any time for air molecules to move into the area between the blades.

#### JimmyRott

##### Expert Member
Hypothetical infinities and rigid mechanical systems gonna get confusing real quick. Why don't you just define an upper limit for the fan speed?
Because then the answer is trivial. Obviously it moves air if its just going really fast.

#### Crush

##### Well-Known Member
Yes and no... concurrently.

#### saor

##### Honorary Master
Because then the answer is trivial. Obviously it moves air if its just going really fast.
If part of the answer involves normal air being unable to fill the space made by infinitely fast moving blades, there's probably a definite (non-infinite) fan speed at which that effect occurs, ie. the blades are moving faster than the air can account for & thus nullifies the fan effect. Seems like infinity isn't required here.

#### JimmyRott

##### Expert Member
If part of the answer involves normal air being unable to fill the space made by infinitely fast moving blades, there's probably a definite (non-infinite) fan speed at which that effect occurs, ie. the blades are moving faster than the air can account for & thus nullifies the fan effect. Seems like infinity isn't required here.
OK, i agree with you. How would you determine that speed though? And for the purposes of this discussion what is the difference between that actual speed and infinity?

#### johncgalloway

##### Senior Member
Wouldn't the air touching the blades basically burst into flames? Turn into superheated plasma?

#### rambo919

##### Expert Member
Somehow I doubt an infinite speed is logically possible for anything nvm physically.

#### ToxicBunny

##### Honorary Master
Wouldn't the air touching the blades basically burst into flames? Turn into superheated plasma?
By and large yes, you would start to possibly look at that sort of effect happening

#### rambo919

##### Expert Member
If it was moving at infinite speed..... might it not appear perhaps to stand still and thus not move any air at all?