|MadSci Network: Environment & Ecology|
Back in the 1940's, Antarctic explorers Paul Siple and Charles Passel measured the amount of time it took a pan of water to freeze, and found that the rate of heat loss from the container could be determined from both air temperature and air movement. From this experiment, the concept of "Wind Chill" was realized.
Wind chill affects the rate of heat loss...not the actual air temperature or the temperature of any object exposed to the air.
Here is one example that well-illustrates the process. If you leave a bucket of water outside when the air temperature is 35 degrees Farenheight, and the wind chill index is 25, will the water freeze? The answer is no. The water will lose heat until it reaches the temperature of the surrounding air. The wind just helps it reach that temperature faster.
And to answer your question about whether or not a car will start just as easily with a temperature of -20 and no wind versus a temperature of -20 with a 40 mph wind. Yes it will, assuming the battery didn't die!
The formula to calculate Wind Chill follows:
WC = 91.4 - (0.474677 - 0.020425 * V + 0.303107 * sqrt(V)) * (91.4 - T)
WC = wind chill
V = wind speed (mph)
T = temperature (F)
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