Let me introduce myself - I am Drippy, the (un)official USGS water-science icon. It is obvious that I am a raindrop, right? After all, we all know that raindrops are shaped, well ... like me. As proof, you've probably seen me on television, in magazines, and in artists' representations. Truth is, I am "Drippy" and actually I am shaped more like a drip falling from a water faucet than a raindrop. The common raindrop is actually shaped more like a hamburger bun!
The best explanation about the shape of raindrops appears on Alistair B. Fraser's Web page titled Bad Rain. Mr. Fraser says:
"The artistic representation of raindrop as presented by popular culture is that of a teardrop. Actually, real raindrops bear scant resemblance to this popular fantasy (except after they have ceased to be raindrops by splattering on a window, say)."
" Virtually everyone from advertisers to illustrators of children's books represent raindrops as being tear-shaped."
"Small raindrops (radius < 1 millimeter (mm)) are spherical; larger ones assume a shape more like that of a hamburger bun. When they get larger than a radius of about 4.5 mm they rapidly become distorted into a shape rather like a parachute with a tube of water around the base --- and then they break up into smaller drops."
"This remarkable evolution results from a tug-of-war between two forces: the surface tension of the water and the pressure of the air pushing up against the bottom of the drop as it falls. When the drop is small, surface tension wins and pulls the drop into a spherical shape. With increasing size, the fall velocity increases and the pressure on the bottom increases causing the raindrop to flatten and even develop a depression. Finally, when the radius exceeds about 4 mm or so, the depression grows almost explosively to form a bag with an annular ring of water and then it breaks up into smaller drops."
Find out why raindrops are different sizes
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Can you guess how many baths you can get from a rainstorm? Visit our Activity Center and find out. |
Sources and more information
• Bad Rain, Alistair B. Fraser, Professor of Meterology, Pennsylvania
State University
• Rain: A Water Resource, USGS General Interest Publication
U.S. Department of the Interior | U.S. Geological Survey
URL: http://ga.water.usgs.gov/edu/raindropshape.html
Page Contact Information: Howard Perlman
Page Last Modified: Friday, 07-Nov-2008 15:45:26 EST
