When a drop of water falls onto a larger body of water, it hovers momentarily before coalescing into the bottom layer. High-speed cameras with speeds of 10,000 frames per second shows that the merging process is not instantaneous, but rather takes place in a coalescence cascade such that each step generates a smaller drop. The cascade does not proceed ad infinitum due to viscous effects, as the ratio of inertial forces to viscous decreases as drop diameter decreases in each step of the cascade. Credit: MIT #Science #Physics #Fluids