This aerodynamic force can further deform the largest drops into a sagging dumbbell shape, eventually causing the biggest ones to split into smaller drops. In actual fact, even the hamburger-bun shape, which is based on the observations of single drops in a steady flow, is idealized, particularly in heavy rains. As we shall see later, when rain falls, its drops have many different sizes. Indeed, the smallest drops may not fall at all, being suspended or perhaps forced upward by ascending currents of air until they grow large enough to fall. As a result, there are many collisions between raindrops.
Some collisions cause distortions in the drops' shapes as they bounce off one another.
Others cause drops to coalesce, forming a large drop in the process. And some collisions cause one or both drops to break apart into smaller drops. And as it falls to earth, our drop may grow in size by collecting other drops or perhaps split apart due to collisions or attaining an unstable size. Philipp Lenard was the first to publish experimental results showing the actual shape a raindrop took while falling. Larger drops deformed their shape, having flat bottoms and rounded tops.