greater for larger drops due to their larger mass to drag
ratio. At sea level and without wind, 0.5 mm drizzle
impacts at 2 m/s or 7.2 km/h, while large 5 mm drops impact
at around 9 m/s or 32 km/h.
Rain falling on loosely packed material such as newly fallen
ash can produce dimples that can be fossilized. The air
density dependence of the maximum raindrop diameter together
with fossil raindrop imprints has been used to constrain
the density of the air 2.7 billion years ago.
The sound of raindrops hitting water is caused by bubbles
of air oscillating underwater.
(http://en.wikipedia.org/wiki/Rain)