Attractive and repulsive interactions in joined pairs of floating bubbles*

When bubbles floating on water come in contact, they experience both an attractive force, due to capillarity, and a repulsive force, due to elastic deformations. We perform an experiment to investigate the nature of these interactions in a joined pair of bubbles and their dependence on bubble size and bubble size ratio. The experiment consists of placing two floating bubbles in close proximity on a water tank and tracking their collision and subsequent oscillations. By fitting the oscillations to a simple damped-spring model, we extract the effective spring constant and the damping coefficient of the joined pair as a function of bubble size. We find that the natural frequency of oscillation has a power-law dependence with bubble diameter of the form ω₀ ∝ D^-0.5.