What causes the stability and formation of smoke rings and air rings in water?

[jumpjack]

Take a look at these videos:

Smoke rings in air:
http://www.swisseduc.ch/stromboli/etna/etna00/etna0005video2-it.html?id=14

Air rings in water:
http://www.youtube.com/watch?v=bT-fctr32pE&feature=related

Second one is really amazing, as it shows two things:
- great stability of the ring, which prevents air from escaping the ring itself for a long time
- possibility to "extract" a ring from another

I wonder how it is possible. I think some strange physics law apply here, where "strange" means something like the law which makes a spinning top have the axial precession, and which prevents a giroscope from being rotated perpendicularly to its rotation axis.

If you look at "dolphin rings", you can see that, when a ring is cut, two things happen:
-The dolphin bends a part of the rings, just like if it was a solid thing, and brings the edge of the cut to touch a part of the ring; this makes the edge "join" to the ring, thus creating a secondary ring.
-The remaining part of the old big ring remains alive for a bit, moving toward dolphin body, and it eventually disappears.

I think air particles have two combined movements: a rotation around the "ring axis" (a "circular axis" actually), and a rotation around the axis perpendicular to ring's plane.

I'll try to draw a picture...

 

[jumpjack]

I hope you can see the image:
[URL]http://penolo.com/sketch/r/rrLW.png[/URL]

Maybe you're also able to edit it using this link:
http://penolo.com/rrLW

 

[jumpjack]

so, why do steam/smoke particles remain confined in the "donut"?
And how is it possible an air ring in water can be split and rejoined to a smaller ring?

 

[K^2]

With the water rings, surface tension helps a lot. It prevents air from leaving the vortex. Of course, it also tries to break up the ring into individual bubbles, but that would require breaking up the vortex, which is gyroscopically stabilized. Basically, the vortex is created first, and the air is injected by the dolphin. The centrifugal effect within the vortex basically means that air "rises" towards the core-circle of the vortex, where rotational speed is the lowest.

I do not completely understand the vortex states themselves, but I do know that they tend to have relatively long life-times. That's just something about the dynamics of the gas/fluid, and adding air bubbles or smoke to the gas stream just makes them visible.

 

[pallidin]

That second vid is really neat. Thanks for sharing.