We hear it every winter. When the temperatures are due to dip into the single digits, we’re told that what we really need to watch out for is the wind chill.
But what exactly is wind chill and why is it so dangerous?
What is Wind Chill?
The Merriam-Webster dictionary defines wind chill as “ a still-air temperature that would have the same cooling effect on exposed human skin as a given combination of temperature and wind speed”.
In simpler language, wind chill is a measure of how cold it actually feels outside with the wind taken into account. In fact, many meteorologists prefer the expression “feels-like” temperature to the term wind chill.
Despite the fact that it is often reported in degrees, wind chill is not an actual temperature.
Instead, wind chill is a measure of how quickly heat is lost from an object.
To understand how it works, we will need to briefly review the science of heat.
The Science of Heat
Heat is a form of energy that is transferred as a result of temperature differences.
If you consider two objects with different temperatures which are exposed to one another, heat will always transfer from the object at the higher temperature to the object at the lower temperature.
In other words, heat always travels from something hot to something cold.
When you touch an object and it feels cold, what you’re actually feeling is heat leaving your body and transferring to the other cooler object.
In fact, did you know that there’s no such thing as cold? There is only absence of heat. Don’t believe me? Check out this video at the bottom of this page.
(I know this is sounding complicated, but stick with me).
Human Body Temperature
As humans, we generate our own heat—this is why we are considered warm-blooded.
Our bodies are designed to keep us at a constant temperature, approximately 98.6 degrees F. When we are overheated, we sweat. As the sweat evaporates from our skin, it takes body heat with it and cools the body.
(Try it: wet the back of your hand. The wet place on your hand will quickly start to feel cool as the liquid evaporates from it).
When we are cold, we shiver. This action expends energy and raises our body temperature.
Our bodies are constantly monitoring our temperature and responding—keeping us at the optimal temperature for our life processes to take place. This is an example of homeostasis.
What Happens When We are Exposed to Wind Chill
When you step outside on a cold day, your body temperature doesn’t immediately drop to the outside temperature. Because you are warm-blooded, your body continues to generate heat and insulate you with a thin layer of warm air.
However, if the wind picks up, it will blow away the thin layer of warm air that is insulating you—exposing your skin to the cold temperatures. Your body, sensing the cold air against your skin, responds by generating more heat and forming another layer of warm, insulating air. As the wind continues to blow, this process is repeated. The harder the wind blows, the faster it takes place. Once the wind reaches a certain speed, your body can no longer produce heat fast enough to counter the effects of the cold outside air.
This is the basis of wind chill.
Wind chill can be dangerous, especially when outside temperatures are below freezing. Without the layer of warm air insulating you, heat will continue to leave your body. In fact, the outermost layer of your skin can drop to match the outside temperature resulting in frostbite. The chart below shows the amount of time it takes to get frostbite on exposed skin at different wind chill values.
If you continue to remain outside, you could develop hypothermia as your core body temperature drops below 95 degrees F.
How to Protect Yourself from Wind Chill
If you must be outdoors when wind chill is a factor, take steps to protect yourself.
Wet clothing can quickly draw heat away from your body.
Limit areas of exposed skin. Wear a hat, as body heat is easily lost through an uncovered head.
Dress in Layers
Trapped air between layers of clothing provides additional insulation.
Protect Yourself from the Wind
If possible, shield yourself from the wind.
Science Experiments Involving Wind Chill (Even if it’s not Cold Where You Live)
You (or your students) can easily experiment with wind chill. In fact, I’d wager that you’ve employed the principles of wind chill already.
Every time you’ve blown on a hot bowl of soup to cool it, you were using wind chill. Your breath pushed away the top layer of warm air from the soup, leaving the top layer of liquid exposed to the cooler air and lowering its temperature. Because heat always transfers from something warmer to something colder, warm liquid then rises to the top of the bowl, transferring its heat to warm the air above it. As heat continues to be lost, your soup cools to a palatable temperature.
Here are links to additional experiments involving wind chill:
And here are some fun science activities to do in the frigid temperatures. Just be sure to bundle up, protect your skin, and watch out for those wind chills!