Mark S Bilk wrote:
> You can make a smoke-ring type air pulse generator using > a cylindrical tube with a rubber membrane covering one > end. Thump the membrane (or pull on the center and then > let go) and it shoots a toroidal soliton of air that you > can feel across a room. (Wonder how a cat would react > to it? >8^) I'm told a 3 pound coffee can with a round hole cut in the bottom works well. You put the plastic cover on it, and thump the plastic cover to spit out the rings. Inside the can, you put ?? and ??, which are common chemicals but which ones I can't recall off hand; they're commonly used together to make "smoke" in high school chemistry classes (mine was too long ago and so I've lost the names). As to cats, I'm told that, smoke or no smoke, cats find it very weird when you "touch" them with a vortex from across the room. These memories come to you courtesy of my first programming job, which was in a sort of commune-like atmosphere where folks spent a lot of time doing stuff that wasn't very "productive". I joined them some time after the coffee can vortex "experiments" were done, and consequently heard about them but wasn't a participant. > There's a commercial toy like this, but > I don't remember the length:width ratio, which may be > critical. I vaguely recall it being about 2:1. The commercial toy is -- or was, back when I had one -- extremely noisy. From Whammo, as I recall, but the name of the toy is long since lost. It was an air gun, and sounded like it. It apparently used a rubber diaphragm about 6" across, if I can judge by the shape and size of it. The front of the gun was shaped like a funnel, but with smoothly curved sides, as though they wanted to reduce the volume of the "combustion chamber" to get as much overpressure as possible during discharge. Of course the shape of the chamber doesn't affect the total volume of air coming out the front, which only depends on the size of the diaphragm and the distance it's pulled back, but it might affect the velocity. I still recall the totally ludicrous TV ads for the thing. One in particular stands out: It showed a child watching a grownup start to light a cigarette. The child, who was 'way off across the room from the grownup, fires the gun at the critical moment, and blows out the match before the guy gets his cig lit. Now the funny bit: The guy with the cig looks all around, trying to figure out who did it. Very funny indeed, after meeting the gun in person -- clearly the man in the ad was *deaf*, otherwise he'd have known exactly what happened, due to the BANG! when the gun fired. > Maybe > a Morton salt box would work, but I think the toy I saw > was 2 or 3 times that size. > > Maybe the spark is simply causing a temperature jump in the > air inside the tube, causing it to expand suddenly and shoot > a small vortex ring, as you suspect. (Is a smoke-ring > properly called a "vortex"?) That would explain why the > hoped-for "force beam" can't go through metal or plastic. > > Another approach to visualize an air pulse would be a > wide-angle schlieren system with a high-speed video camera. > Maybe at a local university? If the air is warm it might > refract light enough to show up. > > http://en.wikipedia.org/wiki/Schlieren > > Mark >
