Wind Chill Factor Formula ```Name: N/A Status: N/A Age: N/A Location: N/A Country: N/A Date: N/A ``` Question: I would like to know what the actual formula is to calculate the wind chill factor. Or is there such a thing? Replies: I do not know if there is a formula, but I seem to recall (this was learned way back in high school so no guarantees) that it was evaluated by take the temperature of a wet thermometer at a particular wind speed and comparing that to a dry thermometer - this gives you a temperature decrease caused by the wind evaporating water that should closely approximate the effect of wind on the human body. I assume the wind chill factors quoted by weather people are derived from tables of this sort... Check out: http://observe.ivv.nasa.gov/nasa/earth/wind_chill_applet.html Actually, different countries use different measures of wind chill and different units even... The relevant quantity is not the final temperature as I said earlier, but the rate of heat loss per unit area of exposed skin. There are formulas for heat loss (I think there is one ascribed to Newton) but basically in still air it goes linearly in the temperature difference between the inside (body temperature) and the air outside. When it is windy the heat loss is increased due to evaporation of water from the surface of your skin. The "wind-chill factor" then gives an equivalent temperature that it would have to be outside in still air for the same rate of heat loss that you get in still air with the current wind. I think it is possible that in a really strong wind the effective temperature could go below absolute zero, which would not make too much sense from a temperature perspective - just that the heat loss rate is greater than you could ever get by standing in still air no matter how cold. Anyway, that is the basic idea. Arthur Smith Click here to return to the Physics Archives

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