Physics Photo of the Week
Warren Wilson College
Feb. 4, 2005
Icicles - again, again, and again!
February 3, 2005
December 13, 2003
February 16, 2003
In three successive winters, this old windmill, homemade
from an old bicycle wheel, has experienced an ice storm in each
winter. The latest was this week! These ice storms occur
during winter storms when rain falls on objects that are colder than
the freezing point of water. It is usually quite windy during ice
storms, and this windmill spins quite rapidly during the rainy, windy
weather. As the wheel is spinning rapidly, the centrifugal force
that the water drops experience due to the rotating rim, causes an
outward force (centrifugal force) on the water drops as they freeze,
forming the icicles pointing outward from the hub. No major
damage occurred in the area for any of these icestorms.
Last winters' ice storm was quite impressive (center photo) and the
icicles reached a length of about 5 cm (1 1/2 inches). Notice
also that the long icicles grew not exactly radially outward but tend
to lean counter-clockwise in the photo. This is attributable to
air friction as the wheel was spinning rapidly. The resultant
force on the icicles was the vector combination of the retarding air
friction (counter-clockwise) and the outward centrifugal force.
The wheel was spinning clockwise.
The photo from two years ago (right) was featured in an earlier web
page, which the author published before the regular Physics Photo
of the Week and was also published in The
Physics Teacher in February, 2004.
Below are two close-up photos of this week's and last winter's
Notice the optical properties of the icicles: The land-sky as seen
through the lens-like icicles is inverted. Each icicle acts as a
crude cylindrical lens, which inverts the image only in the direction
perpendicular to the axis of the cylinder. Donald F. Collins
Physics Photo of the Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to firstname.lastname@example.org.
here to see all Physics Photo of the Week for 2005
to see all Physics Photo of the Week for 2004.