THE SHAPE OF RAINDROPS
Most people and even many engineers would guess that the shape of a raindrop is the familiar teardrop shape:
Cartoon tear drop
However, the above teardrop shape appears only in cartoons and the real shape is closer to the flattened hamburger bun shape seen in the photos at the right. In each case the water drop is falling through still air. That is, the velocity of each is downward. The scale of the pictures is roughly the same so that the lower drop is roughly half the diameter of the upper drop.
The incorrect assumption about the shape of liquid drops is so common that it has merited an entry in the Bad Science Page.
The shape and size of the raindrop is determined by the relative strengths of surface tension and hydrodynamic forces. To learn a bit more about the physics leading to the shape of raindrops click at the highlighted text.
I’ve expanded this page beyond what was done on the previous version of the web page by including detailed discussions of the maximum size of raindrops and the speed of raindrops. In the latter section, I have also added a discussion and estimate of the force of a typical droplet as it strikes a horizontal surface. These discussions came out of a classroom presentation that I did in one of our fluid mechanics classes.