Analytical Instability Model for the Separation of a Sphere From a Flat in the Presence of a Liquid Film

An instability model is proposed to describe the process of separating a sphere from a flat in the presence of a lubricant. The model is based on consideration of the effects of sphere inertia in characterizing the critical point of separation — namely, that there is a sudden onset of significant sphere acceleration. Good agreement is found between the predictions of the instability model with those of a full numerical simulation. The instability model provides an improvement over an “impulse” model found in the literature, which is unable to predict the point of separation.