Significant intervals of energy transforms in bubbles freely oscillating in liquids

A wall motion of a bubble freely oscillating in a liquid is studied from the point of view of energy conversions at different instants. It is shown that the time of the bubble oscillation can be divided into two distinct intervals. In the first long interval （here called PK and KP intervals） the prevailing energy conversion is between the potential energy of the bubble and the kinetic energy of the liquid. In the second short interval （here called KI and IK intervals） the kinetic energy of the liquid is transformed into the internal energy of the gas/vapor in the bubble interior and into some other forms of energy. By observing the bubble wall motion in the PK and KP intervals, it is shown that only the value of the maximum bubble radius in the corresponding oscillation can be determined. However, only the knowledge of the maximum bubble radii is insufficient for formulation of a correct theoretical model. Unfortunately this fact is often not noticed in the literature.