Winter Wonders: The Science of Cold

When it comes to science, temperature matters. And when it comes to Wisconsin, things get really, really cold. When the temperature drops, the world around us changes in a practical and scientific sense. For instance, my car is less likely to work (though that may be a function of age rather than weather), and the percentage of water maintaining a crystalline configuration goes up. There are a lot of things to wonder about how a cold world functions, scientifically. These are some of my questions, and their answers:

1. Will the gasoline in my car?s tank actually ever freeze into a gas-cube?

Thankfully, no. Even though the car doors might freeze shut, the gasoline will remain conveniently liquid. Gasoline, or petrol if you?re so inclined, is a mixture of substances, namely different kinds of hydrocarbons. Each hydrocarbon freezes at a different temperature. So the overall freezing point of gasoline is hard to pinpoint, but assuredly is quite low. Hydrocarbons solidify at varying degrees of cold, with the ?warmest? freezing point around -77? F/-25? C and the coolest was -320? F/-160? C (Smittenberg et al. 18).

Bonus fact: Frozen fuel is more of a concern for airplanes, but there are ways to lower the freezing point of jet fuel. For instance, US Patent 7,666,294 B2 was issued last year to Shell Oil Company for a method of mixing in non-petroleum derived fuel to depress the point at which jet fuel freezes (Bauldreau).

2. Why is wool so warm?

On the coldest days in Wisconsin, my toes? best chance at avoiding numbness lie in a thick pair of wool socks. Wool keeps out the cold because it is an excellent insulator. Crimped and crisscrossed woolen fibers create tons of little air pockets. The tiny air masses within my socks have difficulty moving in and out of the fabric. Without convective heat transfer and contact with air of other temperatures, the spaces between wool fibers maintains a steady temperature. That temperature is warmer than winter?s, allowing wool to form a welcoming cocoon with warm, stagnant air.

3. Why do some snowflakes look intricate and lacy, while others seem shapeless?

Sometimes a snowflake drifts down from the sky and lands on my coat sleeve as a symmetrical, stunning surprise. But other times it seems as though the sky is simply dropping softly frozen clumps. Of interest for centuries, the delicacy and variability of frozen precipitation was even studied by the likes of Johannes Kepler and Ren? Descartes. In 1954, a Japanese physicist, Ukichiro Nakaya, classified types of snowflakes for the first time. The current system for making sense of snowflake formation is based on two factors: temperature and humidity.

The two main snowflake, or snow crystal, shapes, are plates and columns (Libbrecht 860). Plates are the typical hexagonal flakes and columns are elongated, blocky crystals. As a cloud?s temperature moves below 32? F(0? C), it will pass through various phases of crystalline potential (Libbrecht 860). If enough water is present in a cloud, between 32 and 23? F (0 and -5? C), plates will form, sending small six-armed flakes to the earth. In the 23 to 14? F (-5 to -10? C) range, a cloud produces columnar snow crystals.

Below 14? F (-10? C), snow?s crystalline shape switches back to plates again, but larger ones this time. In all of these temperature ranges, the amount of moisture in the air affects the final shape and size of the crystal.

The science of snowflakes is fascinating and to learn more (or just to see some awesome images) I have a couple recommendations. If you?re interested to see a graphic representation of various crystals forming at different temperature and humidities, I recommend page 860 of ?The physics of snow crystals.? Or check out old-school sketches of 80 simple but fascinating snow crystals by Magono and Lee in a modification of Nakaya?s classification system: ?Meteorological classification of natural snow crystals.?

Finally, and I have to say this is a winter wonder must, check out these stereo images of snow. As for me, I am eagerly awaiting the next snowfall, to see if I can guess the temperature and humidity of the cloud in which the snow crystals formed.

References:

Bauldreay, J. M., Heins, R. J., and Smith, J. ?Depressed freeze point kerosene fuel compositions and methods of making and using same.? Patent 7,666,294. 23 Feb 2010.

Libbrecht, K. G. ?The physics of snow crystals.? Reports on Progress in Physics. 68 (2005): 855-895.

Smittenberg, J., Hoog, H., and Henkes, R. A. ?Freezing points of a number of hydrocarbons of the gasoline boiling range and some of their binary mixtures.? Journal of the American Chemical Society. 60 (1938): 17-22.

Image Credits: Wool: Photo by Marc Pehkonen, courtesy of Fuzbaby.com; Snowflakes:Electron and Confocal Microscopy Laboratory, Agricultural Research Service, U. S. Department of Agriculture.

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