Air bubbles are supposed to rise in water, am I wrong? [ame=http://www.youtube.com/watch?v=TMCf7SNUb-Q]YouTube - Dolphin play bubble rings[/ame]
You are right for typical air bubbles in water. The "bubbles" the dolphins are blowing are anything but typical. They are "vortex rings;" air rotating around a central axis in the ring. The outer edge of the ring is moving contrary to the direction of travel of the ring. I suspect that the dolphins shoot the rings slightly downward so that they pull themselves downward, pretty much balancing their inherent buoyancy. The rotation in the ring is gradually slowed by contact with the water; If the video is long enough, the ring will start to move towards the surface. Air-in-air vortex rings are easily made and typically made visible with smoke or water vapor. I know this because I do a Energy in Motion; Vortex Ring Investigation activity with middle schoolers about 15 times a year.
Tom, All my experience; many months of research, experimentation and development, is with air-in-air vortex rings. So, I'm little shy on the air-in-water sort. I've seen Utube videos of people blowing air-in-water rings in a pool. They are always lying on their backs, blowing straight up or nearly so. It looks like the air is propelled solely with jaw/cheek/tongue movements. The rings rise and expand rapidly. I suspect that the tightness of the dolphins' rings is due to a very well developed ability to use their diaphragms to get a brief high velocity charge of air, and a sharp ending cut-off. Have you ever seen a human blow a ring in water other than straight up? If so, how did they do it?
Yes, but it doesn't stay formed for very long. It's much easier to do it on your back. Humans don't have a lot of lung power, so it's much easier to have buoyancy help. Going sideways, the rings break up quickly. I always use my lungs to expel the air, but shape the pulse with my lips and tongue. Tom
