Why are raindrops always round?
Raindrops are not always round. They are "tear-shaped" blunt end down due
to air resistance.
Molecules that are alike tend to stick together. When drops of water are in
free-fall -- as is the case with raindrops -- the molecules' mutual
attraction for each other pull the water drop into the shape of a tiny
sphere because that shape has the smallest surface area that the piece
(drop) of water can take on itself.
This is true for any liquid. Tiny drops in free-fall are always round
A drop is round, if it is not falling through
the air (in other words, if it is suspended in the
air or in another fluid). When falling through the
air, the bottom of the drop is flattened somewhat
by the air that it is moving through.
However, drops are round because of a property of
the physics of liquids called surface tension. A round
shape is the easiest to maintain. If you start
a mass of liquid out with another shape (like a cube),
it will want to round out any corners and
become a drop, or if in a container, it will want
to take the shape of the container.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
Under undisturbed conditions, raindrops would be round, caused by the
surface tension of the droplet, but their motion and environment causes
changes to their shape. Raindrops form from very small spherical water
droplets, and begin to fall to earth due to gravity. This movement causes
the raindrops to be more oval-shaped on the bottom, and more flat on top,
similar to an English muffin or biscuit. Air currents can distort the shape
even further, and sometimes cause the drops to break up into smaller drops.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Update: June 2012