Dear Tom,
Because rain falls so far from the clouds, why doesn't it damage whatever it
hits? For example, you would think raindrops would break my car windshield.
Is it more a physics question as opposed to a weather question?
Tami Stevenson, Elgin, Ill.
Dear Tami,
It's a question of physics -- the physics of raindrop stability. As a large
raindrop falls faster and faster through the air, the friction of its
passage through the air causes it to flatten, then to bulge upward in the
middle rather like an inverted paper bag, and finally to shatter into
smaller drops that fall more slowly.
It turns out the maximum size that a raindrop can attain before shattering
is 0.2 of an inch in diameter. The top fall speed of the largest "shatter-proof"
raindrops occurs when frictional drag equals the weight of the drop, and
that's 21 m.p.h. Fortunately, raindrops 0.2 of an inch across falling at 21 m.p.h.
don't cause damage.
