Need of physics people (not game related)

Okay, so I noticed something weird earlier while playing with a CPU fan. So I hooked it up to my power supply (which just happened to be an AC -> DC converter that used to be a cell phone charger till I hacked the end off, in line with a 9 volt battery, don’t know what I’m really thinking lol, probably dangerous) and hold it where it’s blowing the air upward, and it does the normal fan thing, blows air, upward and sucks air in from below/maybe a minor amount from the side. But, if I lower it to approximately 3 mm / one fourth of an inch from the table, it changes, it only blows air out at about a 40 degree angle and higher (small cone of no air flow) and it picks up speed… can any one tell me why this is… I could possibly post a few pictures if needed to explain.

May be picking up speed because when it’s that low, air has trouble getting to it fast enough? :confused:

Well, from what I understand, it should be quite the opposite of that. The fact that it’s speeding up means it’s doing less work, one way or another. So some how, being low to the table makes the air flow more easily into the fan, atleast that’s the only explanation I can think of. I can’t see it eliminating work anywhere else.

Trouble air getting to it fast engough?
It´s air, a composite of gases we are talking about, not honey or oil.

I am sure it doesn´t pick up speed, its an acustic illusion ^^ (you can read it out though if you got an yellow RPM connector at the fan)

Lowering above the table causes tiny vortexes to form, changing the pitch of the sound as the blades of the fans cut through the vortexes, making you perceive it as turning faster because it gets louder and changes pitch.
Additional lowering the fan, idd leaves less width for the same amount of air to be sucked in. If the fan is designed to move 100m3 of air per hour, it will do, no matter if it sucks it in through a drinking straw or a window, the only difference will be, that the air has to have a much higher speed in the drinking straw, to balance the local underpressure the fan causes. The speeding up of the air, also causes noise.

And the fan “not blowing” over the table is just that the airstream is pointed into a different direction due to the vortexes forming between table and fan.
Grab a fog machine to make it visible or buy one of those tiny smokebombs for kids in the next store, and if neither is at hand, take a tabletennisball, cut it into tiny pieces, put it on tinfoil, make a small ball and light the tabletennisballpieces, but do it ouside, its not really healthy smoke and it smokes like hell and don´t touch it afterwards its burning hot.

There are also plenty of ways to make DIY smoke bombs out of household chemicals, but if you take the risk, the money to buy the chemicals and the time it takes to produce, you´r better off buying them somwhere, so I wouldn´t bother to google for it ^^

Alright, it does have the yellow wire, but what would I hook that up to to read it?

I’m quite sure there are some limitations on available air space that will make what you said about it moving so much air per hour false, similar to a cars intake. But I definitely understand what you mean.