How does the windchill factor work?

You have probably heard weatherpeople on the TV news talking about the windchill factor. The windchill factor is the temperature that a person feels because of the wind. For example, if a thermometer reads 35 degrees Fahrenheit outside and the wind is blowing at 25 miles per hour (mph), the windchill factor causes it to feel like it is 8 degrees F. In other words, your 98-degree body loses heat as though it is 8 degrees outside.

The windchill factor is the same effect that causes you to blow on hot soup to cool it down. The movement of the air increases the soup's loss of heat by convection, so the soup cools down faster. See How Thermoses Work for details on radiation, conduction and convection.

For an inanimate object, windchill has an effect if the object is warm. For example, say that you fill two glasses with the same amount of 100-degree water. You put one glass in your refrigerator, which is at 35 degrees, and one outside, where it is 35 degrees and the wind is blowing at 25 mph (so the windchill makes it feel like 8 degrees). The glass outside will get cold quicker than the glass in the refrigerator because of the wind. However, the glass outside will not get colder than 35 degrees -- the air is 35 degrees whether it is moving or not. That is why the thermometer reads 35 degrees even though it feels like 8 degrees.

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