Answer to why
ice builds up evenly on
all sides of stems, twigs, and wires.
As can be seen in
photo, the ice builds up evenly on all sides of twigs and wires and
bicycle spokes. The reason it builds evenly on all sides is due
to surface tension. Any twig that gets wet in the rain gets wet
all the way around, not just the top or the side where the wind comes
from. Raindrops tend to adhere to most surfaces due to surface
tension. For single raindrops (smaller than 1 mm diameter) the
surface tension forces are much greater than gravity forces. Even
as the ice grows, the surface tension effects cause the ice to grow
uniformly. If the rain falls faster than it freezes, then gravity
(or centrifugal forces in the spinning wheel) will dominate for the
bulk of the water and form icicles.
The surface tension effect is not so noticeable when the rain freezes
on a larger surface such as a board fence in the picture below.
surface of the boards on the fence are large enough so that the weight
of the film of water adhering to the surface dominates the surface
tension forces. The result can be seen by the formation of
icicles on the bottom edge of the boards. If one looks carefully,
the effects of the wind are also noticeable as the icicles slope
slightly in the direction of the wind.
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