From Drips to IceNathan CorbusierAward: Top 100
School: minnetonka high school The physics concept present in this photo of an icicle is conduction. Icicles' unique shape, and characteristic melting at freezing temperatures, is due to conduction. Icicles begin their life cycle from small drops of water freezing on the bottom of objects, dripping towards earth. Once ice has accumulated enough that melting and freezing only replaces ice, the ice begins the growth pattern of an icicle. An icicle grows when a pendant drop forms at the tip, which grows and then falls. This leaves behind a small bit of ice, growing the icicle. The vertical growth of icicles is 20-60 times faster than horizontal, meaning the pendant drop melts 20-60 times faster than the rest of the icicle. Because mass cannot change unevenly in the icicle, at the icicle's tip, ice forms around unfrozen water. The water cannot freeze because temperature inside the icicle walls is below freezing, which forces conduction out of the root (top) of the icicle to lower the temperature. That is why in this photo, the root is not the thickest part of the icicle, because it is open to the air. The icicle walls thicken when supercooled water constantly is present on the ice walls, with some of the water occasionally freezing. This condition is called spongy ice, which the icicle constantly experiences during growth. This is how conduction plays an important role in one of nature's most curious phenomena. 
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