Traditional researches on this topic have been associated with cavitation erosion. Recent researches are associated with medical applications, sonochemistry and ultrasonic cleaning. We have developed weakly compressible theory and a grid-free numerical model for this phenomenon,modelled both the first- and subsequent-cycles of oscillation, and showed that the energy of a transient bubble follows a step function in time, being nearly conserved for most of each cycle of oscillation but decreasing rapidly and significantly at bubble inception and at the end of collapse, due to the emission of shock waves.