Raindrops

Raindrops are liquid water droplets that reach the Earth's surface as precipitation. They form in clouds when water vapor condenses and droplets collide and coalesce, growing larger until gravity overcomes updrafts. In some clouds, precipitation begins with ice crystals that melt into liquid drops, a process common in warm-layer rain.

Typical raindrop sizes range from about 0.5 to 5 millimeters in diameter. Small drops are nearly spherical, but as diameter increases they deform under air resistance and become oblate, with the bottom flattened. Very large drops can become pear-shaped or may fragment in midair due to aerodynamic forces.

Drops fall with a terminal velocity determined by their size, shape, and the density of the air. Small drops may fall at around 2 meters per second, while larger ones can reach several meters per second, up to roughly 9 m/s. Their motion is influenced by wind and turbulence, and larger drops are more prone to fragmentation during transport or on impact with surfaces.

On impact, raindrops splash and create secondary droplets. In the atmosphere, they scatter and absorb light, affecting visibility and contributing to optical phenomena such as rainbows, which arise from refraction and dispersion of sunlight in the droplets. The distribution of raindrop sizes, known as the drop size distribution, is a key factor in describing rainfall intensity and is studied in hydrology and meteorology using specialized instruments.