Unlike the water beads that drip from your bathroom faucet, rain-drops are not tear-shaped. They are fattened globules having somewhat concave bottom. Other things being equal, all droplets of water are spherical, the most compact of shapes. Raindrops begin their fall as spheres and would arrive that way but for the pounding that they receive from two intervening forces.
The first of these sculptors is hydrostatic pressure, which causes the bottom portion of a liquid mass to compress and flatten in response to the weight of the upper portion. Although raindrops are feather light, they are subject to this phenomenon and are shaped by it. As the drops fall, aerodynamic pressure – the force of air on an object moving through it – resists their downward course and indents their bottoms. That’s the second influence.
The largest raindrops are the most affected. Many drops are destroyed entirely and burst into countless watery bits – each sustaining yet more distortion until a pavement, lawn or your umbrella ends its fall. The diameter of most raindrops ranges from 0.5 to 6 millimeters. The largest drops fall at the rate of nearly 9 meters per second, whereas the smallest have a leisurely speed of 2 meters per second.