It is now obvious that this should have been in [TECH] Who would have though ? :-). >> They aren't that hard to blow yourself > Yes; I've seen scuba divers blow air rings. =A0Usually straight upward, > and without any of the fine control that the dolphins show. > A really interesting question is whether the dolphins got to observe a > human blowing air rings before they tried it themselves... The paper notes that rings form spontaneously from air bubble of more than a certain size. Ref as before, from =A0 =A0 =A0 =A0http://faculty.vetmed.ucdavis.edu/faculty/bjmccowan/Pubs/McC= owanetal.JCP.2000.pdf Pressure inside the bubble equals the mean pressure outside it, and pressure below is higher than pressure above due to hydrostatic head. There is a net uplift in the middle of the bubble at the bottom which tends to flatten the bubble and when the surface tension is exceeded by the hydrostatic forces the middle "punches through and a torus forms. I suppose that the surface tension tends to rapidly pull the inner towards the outsides, extending the hole diameter. For rings blown at an angle forces will differ from this, but a central water jet or even the tendency to extend outwards from a high speed central air stream probably (and apparently) cause the middle to rupture. Once any sort of middle hole is formed surface tension forces will act to equalise forces throughout. The flow through the centre rolls the ring and starts the vortex. Their description comes from a Scientific American article which is barred to all those not paid up for access. Ref at end\ ____________________ _____________________ Small but highly educational black hole: Hmm - Googling their text on formation located this Which explains that & how Mumpback whales form circular "corrals" =A0to herd and then trap fish - one whale creates a circular ring 10+ metres across and then a leader signals the "attack" and astring of whales rise trhough the centre, mouths open, to feed. "Bubble Nets & Torodial Air-Core Vortex Rings" =A0 =A0 =A0http://mikenish.com/FHL/?p=3D743 Sounds unlikely? Sure - but here's a video thereof or an extremely good makeup. Note circle of bursting of bubbles in ring on water surface and initialsomewhat spiral shape - this may be due to formation motion or making an intended path for fish to be driven down. =A0 =A0 =A0 =A0 =A0 =A0 =A0http://www.youtube.com/watch?v=3DvJvfjiCTvq4 _____________________ And, Belluga whales doing it differently. A diver primes their mouths with air from his tank and they then blow fast horizontal rings at selected targets. In some cases spectators viewing through glass are accurately targeted. Impressive both for the rings and what it shows of Beluga's mental and physical capabilities. =A0 =A0 =A0http://videosift.com/video/Beluga-Whale-Blowing-Bubble-Rings-in-= the-Water How to blow your own. No fish. =A0 =A0 =A0http://www.wikihow.com/Blow-Underwater-Air-Rings ____________ Scientific American "how it works reference" Any spherical bigger than about two centimeters in diameter will quickly become a ring because of the difference in water pressure above and below the bubble. Water pressure increases with depth, so the bottom of the bubble experiences a higher pressure than the top does. The pressure from below overcomes the surface tension of the sphere, punching a hole in the center to create a doughnut shape. As water rushes through the hole, a vortex forms around the bubble. Any vortex ring travels in the same direction as the flow through its center; in the case of these simple air rings, the vortex flow, in combination with the air's natural buoyancy, propels the bubbles toward the surface. (p. 84) Marten, K., Shariff, K., Psarakos, S., & White, D. J. (1996, August). Ring bubbles of dolphins. Scientific American, 275, 83-87. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Marten et al =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Reference not available without access auth= ority. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 https://weblogin.washington.edu/ _______________ Braslau-Schneck, S. (1994). Innovative behaviors and synchronization in bottlenosed dolphins. Unpublished master's thesis, University of Hawaii, Honolulu. Herman, L. M. (1986). Cognition and language competencies of bottlenosed dolphins. In R. J. Schusterman, J. A. Thomas, & E G. Wood (Eds.), Dolphin cognition and behavior: A comparative approach (pp. 221-252). I-Iillsdale, NJ: Erlbaum. Herman, L. M., Richards, D. G., & Wolz, J. P. (1984). Comprehension of sentences by bottlenosed dolphins. Cognition, 16, 129-219. Lundgren, T. S., & Mansour, N. N. (1991). Vortex ring bubbles. Journal of Fluid Mechanics, 225, 177-196. Marino, L. (1998). A comparison of encephalization between odontocete cetaceans and anthropoid primates. Brain, Behavior and Evolution, 51,230-238. Marino, L., Reiss, D., & Gallup, G. G., Jr. (1994). Mirror self-recognition in bottlenose dolphins: Implications for comparative investigations of highly dissimilar species. In S. T. Parker, Marten, K., & Psarakos, S. (1994). Evidence of self-awareness in the bottlenose dolphin (Tursiops truncatus). In S. T. Parker, R. W. Mitchell, & M. L. Boccia (Eds.), Self-awareness in animals and humans: Developmental perspectives (pp. 361- 379). New York: Cambridge University Press. Marten, K., Shariff, K., Psarakos, S., & White, D. J. (1996, August). Ring bubbles of dolphins. Scientific American, 275, 83-87. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .