Answer to why ice builds up evenly on all sides of stems, twigs, and wires.

As can be seen in this 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.




The 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. 

Return to PPOW.