Astonishing life of a coalescing drop on a free surface.

We report an interesting feature in the consecutive steps of coalescing of a drop, which is called a cascade of partial coalescence. It is observed that as the secondary drop gets smaller, it bounces higher. We show that the capillary force is the main driving force for this phenomenon. By using ultra-high-speed video, it is revealed that the capillary force at the pinch off pulls the drop to the planar interface. The drop bounces off the interface and moves upward until it reaches the maximum height. A theory is developed that includes the capillary and gravitational forces and predicts this process.