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Cooling by Evaporation Activity //. Homemade Science with Bruce Yeany

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 Physics   |   Science
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Why does a body feel cold when they get out to f the shower or after a dip in the pool? A simple activity that can introduce students to the process of cooling by evaporation.
Essentially evaporation is process of molecular diffusion from the liquid's surface. As it occurs, the atmosphere becomes saturated right at that interface which limits the rate due to vapor pressure. The removal of the vapor at the interface allows more molecules to diffuse allowing the process to continue. Blowing across the surface removes the escaping molecules directly above the surface, keeps it from becoming saturated (reducing vapor pressure) and hastens the process. The faster the air flow, the more quickly the diffused particles are removed allowing a more rapid rate of evaporation The process of removing these molecules is actually an example of Bernoulli's principle, the evaporating molecules get caught in the airstream due to a reduced pressure of the moving air flow. The higher the rate of flow the greater the reduction in vapor pressure hastening the evaporation process.

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