Impact of a water drop on a water bed of varying depth

The dynamics of liquid drop impact on a liquid surface is studied experimentally. The interplay between the inertia forces and surface tension forces during the expansion and contraction of the cavity determines the shape of the cavity. In shallow water, the cavity expansion and retraction are dominated by surface tension forces but in deep water the inertia forces and gravity forces dominate the cavity dynamics. The cavity expansion resembles a source of the potential flow below the surface of the liquid. Time resolved Particle Image Velocimetry (PIV) measurements enable estimates of time variation of the source strength.