Static air bubbles underwater

A physical explanation is given for the existence of stable underwater bubbles in the form of a cylindrical column of air oriented vertically. If all the forces are balanced, it will not rise up against gravity in still water. Air compressibility is the key element of the explanation. When the rates of increase with increasing depth of the air pressure inside the cylinder and the water pressure outside the cylinder are equal, it is possible in theory for the bubble to be stationary, contrary to what intuition may suggest. (C) 2011 Physics Essays Publication. [DOI: 10.4006/1.3555766]