Bubble puzzles in liquid squeeze: Cavitation during compression

We let a steel ball fall on a thin liquid layer. Thereby the liquid was squeezed out from between the falling sphere and the solid boundary, which was made of thick glass, allowing for direct high-speed visualisation of the liquid layer at the point of closest approach. Surprisingly, vapour cavities were created during squeeze, with the liquid forced to change phase to vapour as the sphere approached the boundary and the pressure thus increased. This is a direct contradiction to common preconceptions, where classical theory expects the phase transition from liquid to vapour to occur during depressurisation. We believe that our result is the first direct experimental evidence of the shear-induced cavitation model of Joseph (J. Fluid Mech., 366 (1998) 367).