Why real raindrops are not shaped like the cartoon teardrop
Why is the popular 'teardrop' cartoon shape of a falling raindrop physically wrong, and what shape do real raindrops actually take?
History and references
Settled in 1971 by H. R. Pruppacher and R. L. Pitter, refining H. R. Pruppacher and K. V. Beard's 1970 wind-tunnel photographs.
The teardrop shape is a cartoon convention with no basis in fluid dynamics; a falling drop has no trailing point because there is nothing pulling it upward. Early wind-tunnel photography by Lenard (1904) and later, more careful suspended-drop wind-tunnel work by Pruppacher and Beard (1970) showed that small raindrops (under about 1mm) are nearly spherical, while larger ones flatten on the bottom from air pressure into an oblate 'hamburger-bun' shape, and can even develop a concave base before breaking apart. Pruppacher and Pitter (1971) turned these observations into a semi-empirical theory relating drop shape to size. The result is now standard in cloud physics and radar meteorology, so the status is solidly settled.
The most universally mis-drawn shape in all of popular science turns out to be dictated by a clean balance of surface tension and aerodynamic pressure.
Explanations that circulated
- Raindrops are teardrop-shaped with a pointed top, as drawn in cartoons and weather icons
- Small and large raindrops all have the same characteristic shape
References
- A Semi-Empirical Determination of the Shape of Cloud and Rain Drops028<0086:ASEDOT>2.0.CO;2), H. R. Pruppacher, R. L. Pitter, Journal of the Atmospheric Sciences, 1971
Solutions 0
Sign in or create an account to publish a solution