section_path: Formation/Raindrop impacts
section_name: Raindrop impacts
paragraph_text: Raindrop impacts
  
  Raindrops impact at their terminal velocity, which is greater for larger drops due to their larger mass-to-drag ratio. At sea level and without wind, 0.5 mm (0.020 in) drizzle impacts at 2 m/s (6.6 ft/s) or 7.2 km/h (4.5 mph), while large 5 mm (0.20 in) drops impact at around 9 m/s (30 ft/s) or 32 km/h (20 mph).
  
  Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized, called raindrop impressions. 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.
  
  The METAR code for rain is RA, while the coding for rain showers is SHRA.