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Ice water (or hot water) in one’s veins?

January 15, 2009

A reader asked Rocky — What does this post have to do with the mission of the OneHonestMan Blog? Rocky answers: “There is deception all around us. The deceptions can come from others and from ourselves. Facts that we take for granted in life (and markets) may actually be illusions or rationalizations. This post is an example of that.”

ice1It’s 12 degrees outside, and Rocky’s brother (PhD physicist) reports that he’s pouring HOT water down his gutters to unclog them. Alas, either Rocky’s brother didn’t get the memo from Aristotle, or he slept through an early morning lecture at MIT. According to Mpemba Effect, HOT water often freezes faster than COLD water!

Rocky muses, “Is this an urban myth?”

According to Monwhea Jeng at the University of California, the answer is no! Warm water DOES freeze faster than cold water.

Monwhea writes:
Hot water can in fact freeze faster than cold water for a wide range of experimental conditions. This phenomenon is extremely counter- intuitive, and surprising even to most scientists, but it is in fact real. It has been seen and studied in numerous experiments. While this phenomenon has been known for centuries, and was described by Aristotle, Bacon, and Descartes [1-3], it was not introduced to the modern scientific community until 1969, by a Tanzanian high school student named Mpemba. Both the early scientific history of this effect, and the story of Mpemba’s rediscovery of it, are interesting in their own right — Mpemba’s story in particular provides a dramatic parable against making snap judgements about what is impossible. For the full article, click on: http://math.ucr.edu/home/baez/physics/General/hot_water.html

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  1. DanG
    January 15, 2009 at 1:23 am

    The Mpemba effect is interesting, but not relevant to those of us with roof ice dams. Here is a link to a credible Candadian government website about prevention and treatment of ice dams:
    http://www.cmhc-schl.gc.ca/en/co/maho/gemare/gemare_006.cfm
    Cutting paths using hot water is listed as a technique with moderate success. The website says:

    This is actually rather effective if you can get hot water very close to the ice (50 to 100 cm — about 2 ft.) and prevent the hose and nozzle from freezing (Figure 4). The drain must first be freed of ice, so that the water can drain away. However, this means you will be undercutting the mass of ice above you, and this ice may come down.

    The only safe way to do this job is to cut thin slices off the ice — about 30 cm (1 ft.) — all the way from the gutter up the roof. Keep your ladder off to the side, so it won’t be hit by ice coming off the roof.

    Hot water jets from regular garden hoses proved very effective on metal sheds and glass sunrooms when directed from dormer windows above. Do not walk on metal or glass roofs. Cut the ice into sections with the jet, then flood the glass to unhook and slide the ice off. Windows below may need protection from rebounding ice.

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