The fan effect | Science



We were wondering last week, in relation to the poor thermal conductivity of the air, if it is cooler a short-sleeved shirt or a long-sleeved shirt. And the surprising answer is that, on equal fabric, the shirt is cooler, because being more comfortable, the air circulates better between the fabric and the skin and conveys body heat by convection. On the contrary, the shirt, being tight to the body, retains a thin layer of air that acts as an insulator. In fact, the typical tank top that many men wear under the shirt precisely fulfills the function of avoiding sudden changes in temperature in the torso and back, in order to prevent colds, lumbago and other discomfort.

For the same reason, two blankets of one centimeter thick, one on top of the other, shelter more than a two-centimeter blanket, because the layer of air trapped between them helps to retain heat like a third blanket.

A jersey serves little in water, because, unlike air, water is a good thermal conductor, and although wool hinders the circulation of water in contact with the body, heat escapes quickly by conduction.

And, yes, in case of trouble a newspaper can protect us from the cold, if we spread several sheets between two layers of clothes, or between clothes and skin, or between the bedspread and the sheet of a precarious bed. Motorists and cyclists sometimes protect their chests in this way, to avoid cooling due to the rapid renewal of air caused by the frontal current.

As for the botijo, fanning it or focusing on it the current of a fan will favor the evaporation of the water that permeates its body of porous clay - and therefore will increase the cooling of the water - in two ways: on the one hand, it renews the air that surrounds and, on the other hand, the Venturi effect slightly decreases the pressure of the incident air, which also favors evaporation.

And speaking - once again - of the Venturi effect, yesterday, while drinking a very hot tea in front of the fireplace, I benefited from it in two ways. How?

Knowledge occupies place

You can not talk about effects and fans without mentioning the "fan effect", which has nothing to do with refrigeration, but with the theory of information and cognition. It is called fan effect to the fact that handle a greater amount of data on the same subject involves an increase in the time of recognition of the relevant information in relation to that matter. It seems logical that it takes longer to process a larger amount of data; but this brings us to a paradoxical conclusion, since ...

What paradox involves the fan effect, and why is it called that?

Carlo Frabetti He is a writer and mathematician, a member of the New York Academy of Sciences. He has published more than 50 scientific dissemination works for adults, children and young people, among them Damn physics, Damn mathematics or The big game. He was a screenwriter The Cristal ball

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