As ubiquitous as "Have a good day" is the farewell caution heard this time of year: "Be careful; it's slippery out there."
Indeed it can be, if there's ice about. Ice is slippery, as is commonplace in vast areas of the planet, yet exactly why it's slippery remains incompletely understood.
Not for want of people trying to understand. Although most of us tend simply to accept that ice is slippery but most other solids - glass, steel, wood, ceramics, etc. - aren't, there's always a curious few who have to know why. A very few solids are what can be thought of as slippery: graphite, Teflon, carbon nanotubes, molybdenum disulfide.
And there are solids that when wet with water, for instance, become slippery: glass, highly polished metal and the floors and floor coverings certain commercial buildings install where rainwater or snow that will turn to water can easily be tracked in. Go figger.
Anyway, these and other circumstances have attracted attention for a long time. Even Michael Faraday took time out from his pioneering experiments in electromagnetism and discovering that the cowpox insulin used (in 1827) in smallpox vaccination was destroyed by even dilute chlorine gas and could thus no longer produce a reaction when used to vaccinate people - to ponder why ice is slippery.
In 1850, as Kenneth Chang explained in The New York Times, Faraday pressed two cubes of ice against one another and they fused together. He proposed for the first time that ice has an intrinsic liquid layer. Faraday concluded that the liquid layers froze solid when they were no longer at the surface. The liquid layer is too thin to be seen.
I just repeated Faraday's ice cube experiment, for fun. An experiment on ice that's not so easy to replicate involved bombarding an ice surface with electrons, producing a pattern that looked at least partially liquid. ... at temperatures down to minus 235 degrees. That experiment was 146 years post-Faraday. It was confirmed a few years later when helium atoms were bounced off an ice surface.
And so a commonly quoted explanation is wrong that ice is slippery under a shoe or an ice skate because the pressure exerted lowers the melding temperature of the top layer of ice, the ice melts locally and the boot or runner glides on the thin water layer that results. The water layer then refreezes. Nope; the thin water layer is intrinsic.
Researchers being the kinds of people they are, there are folks who aren't as sure as the paragraph above indicates. They think that although the top layer of ice may be liquid, it's too thin to contribute to slipperiness except near the melting temperature, and that is achieved by friction. Pressure, friction, intrinsic water layer ... all those theories about commonplace ice.
Ah, but hold on. Water ice is passing strange. It's unusual that the solid form floats on its liquid because it's less dense. All kinds of wondrous things are a result of that, starting with why Earth is a water planet and not a lifeless dirty icy sphere. Ordinary water ice molecules line up in a hexagonal pattern, called Ice Ih, if formed at atmospheric pressure. At higher pressures, the molecules arrange in crystal structures called, variously, Ice I I, Ice I II, Ice I III, Ice I IV and so on. (At lower pressure, high up in the upper reaches of the atmosphere, ice can form as cubic crystals, cleverly labeled Ice Ic.)
For figure skating, ice at 22 degrees Fahrenheit is preferred For hockey, it's 16 degrees Fahrenheit. "Fast" ice is harder and cooler. "Slow" ice is rougher and warmer.
Field Notes: In olden days, when work and engagements piled up as the year end was in sight, when mail needed to be written and responded to, when work deadlines loomed, when solicitations, magazines and catalogs flooded in and one could see clearly that it wasn't going to be possible ever to catch up and get everything done on time, I would simply plug away until it all was.
That was then, this is now. Just the start of December, but I can foretell that I haven't a chance of attending to all the things I really would like to. Gonna do triage and just do the best I can. Holiday greetings, everyone.
Here are two reminders of dates I hope you will be able to fit in: The Dec. 10 Bird Club meeting and the Dec. 17 Christmas Bird Count.
At the Bird Club meeting, 7:30 p.m. on Sunday in Jackson Town Hall, choices of preferred areas will be arranged by happy individuals and parties who will be participating in the Count. That'll be in addition to a regular meeting, socializing, and a talk on "Incubation Strategies" by Anna Chalfoon. Everyone is welcome. Don't miss this one.
Sunday, Dec. 17, is the date for the Jackson Hole Annual Christmas Bird Count. This is a census of birds entering early winter in a designated area of the Hole and one count of 2,000-plus sites in North America, Central America, and some far-flung locations.
If you just cannot make the Dec. 10 meeting but do want to count birds on the 17th, call Jan Hayse at 733-6700 to confirm. Or show up at 7 a.m. at Jedediah's Original House of Sourdough for pre-Count breakfast and join up then. There will be a post-Count potluck dinner and storytelling that evening starting at 6:30 p.m. at the Jackson campus of Teton Science Schools.
The Christmas Bird Count is a week and a half off, and predicting bird activity is pretty unproductive at any time, so there will be none here. However, think about these birds: a spotted towhee in Wilson on Nov. 27; Sharon Rudd An eastern blue jay, in Alpine; Karen Kruegar; A golden eagle in Victor, Idaho, on Saturday; Brigid Sinram.
© Bert Raynes 2006
Bert Raynes writes weekly on whatever suits his fancy with a dash of news on nature and its many ways.
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