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Ice can refer any of the 14 known solid phases of water. However, in non-scientific contexts, it usually describes ice Ih, which is the most abundant of these phases in Earth's biosphere. This type of ice is a soft, fragile, crystalline solid, which can appear transparent or an opaque bluish-white color depending on the presence of impurities such as air. The addition of other materials such as soil may further alter appearance. The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. However, it can also sublimate from a vapor with no intervening liquid phase such as in the formation of frost. Ice appears in varied forms such as hail, ice cubes, and glaciers. It plays an important role with many meteorological phenomena. The ice caps of the polar regions are of significance for the global climate and particularly the water cycle.
An unusual feature of ice frozen at a pressure of one atmosphere is that the solid is some 8% less dense than liquid water. Ice has a density of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is most dense, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the temperature drops to 0 °C. (In fact, the word "crystal" derives from the Greek word for frost.) This is due to hydrogen bonds forming between the water molecules, which line up molecules less efficiently (in terms of volume) when water is frozen. The result of this is that ice floats on liquid water, an important factor in Earth's climate. Density of ice increases slightly with decreasing temperature (density of ice at at -180 °C (93 K) is 0.9340 g/cm³).
When ice melts, it absorbs as much heat energy (the heat of fusion) as it would take to heat an equivalent mass of water by 80 °C, while its temperature remains a constant 0 °C.
As a crystalline solid, ice is considered a mineral.
Ice can also form icicles, similar to stalactites in appearance, as water drips and re-freezes.

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Model: Canon DIGITAL IXUS 50
Software: Adobe Photoshop CS2 Windows
Exposure Time: 1/501
F-Stop: f/5.6
Focal Length: 5800/1000 mm
Date Taken: 2005-12-29 14:35
Metering Mode: Pattern
Flash: Flash did not fire, compulsory flash mode
File Size: 181 kb

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