Physics Photo of the Week

Warren Wilson College

Feb. 4, 2005

Centrifugal 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 centrifugal icicles.

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

Click here to see all Physics Photo of the Week for 2005

Click here to see all Physics Photo of the Week for 2004.