Today's Wonder of the Day is about a phenomenon that we've all experienced from time to time. Remember the last time you went sledding?
It was probably pretty cold outside, wasn't it? But when the wind would start to blow, it would suddenly feel much colder.
Why is that? Is it magic? Nope! It's just science. Meteorologists call this phenomenon the wind chill factor.
Wind chill is what the air temperature feels like on our exposed skin due to wind. It's always lower than the actual air temperature.
For example, even though the thermometer may indicate it's 35° F (1.6° C) outside, a 25-mile-per-hour wind will make it feel like it's only 8° F (-13.3° C)!
The opposite effect can occur at temperatures above 50° F (10° C). At higher temperatures, humidity on the skin can make the air temperature feel hotter than the actual temperature. Meteorologists call this effect the heat index.
It's important to note that wind chill is a prediction of what experts believe humans will perceive the temperature to be because of the wind. No matter how fast the wind blows, the air temperature is what it is and can be measured by a thermometer.
The wind chill factor, on the other hand, is calculated using various formulas. There is no one formula that all scientists agree on. Most meteorologists in the United States use a standard formula accepted by the National Weather Service.
What causes the wind chill effect? It's a result of the fact that the human body loses heat through a scientific process called convection.
During convection, heated air molecules rise into the air and are replaced by cooler air molecules. How quickly your body loses heat by convection depends on air flow around your body.
Your warm body usually loses heat slowly. When it's windy, though, the wind carries the warm air molecules away from your body more quickly, making you feel colder than the actual air temperature around you.
The faster the wind blows, the faster your body loses heat by convection. As the air temperature around you falls, the effect of wind is magnified, making the wind chill effect greater the colder it gets.
If you've ever blown on a hot bowl of soup to cool it down before eating, you've created your own wind chill effect on your soup!
Even though the air temperature stays the same, the presence of wind makes us feel like it's colder outside than it actually is. The wind chill effect isn't all mental, though.
Since wind chill speeds up heat loss by convection, our bodies experience heat loss and react as if the temperature were as low as it feels…even if the actual air temperature is much higher than the wind chill factor.
Wind chill factors are calculated under the assumption that a person is properly dressed and dry. If you're not wearing suitable outdoor clothing, if your clothes are wet, or if you've been outside for an extended period of time, the wind chill factor will be magnified even further.