Physics Photo of the Week

December 14, 2007

Dew Drop Door
On one morning in late summer this garage door showed these patters of dew condensed on the panels.  Each panel spans the whole width of the door and is about 2 feet high.  Notice that each each panel has no dew condensed on the edges nor on the selected vertical parts of each panel.  The dew is concentrated in the broad center regions of each panel.  This tells us a lot about the construction of the door panels.

The main part of a door panel is thin aluminum.  During the night, the thin aluminum is able to cool appreciably to the environment's
temperature of the outdoors.  Where there are beams along the borders and down the middle of each panel to reinforce the aluminum, the extra mass of the beams takes a longer time to cool to the environment's temperature.  These larger mass regions stay warm throughout the night - above the dew point temperature.  The dew condensate pattern can tell a detective something about the internal construction of an object.  A similar thermal pattern is illustrated in the Feb. 2, 2006 PPOW.

Later in the day, the dew has evaporated and the door appears as shown at right.

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

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