Even a 90-degree summer day is cooler than your body temperature. So why does it feel so warm? You'll find out in this Science Update.
Why doesn't ninety feel chilly? I'm Bob Hirshon and this is Science Update.
Today's Why Is It question comes from Scott Pierce of Seattle, Washington:
If our bodies are 98.6 degrees, then how come we get hot and sweaty if it's anywhere below that–like 85 outside?
We asked Dr. Matthew Kluger of the Medical College of Georgia. He says our bodies constantly generate a lot of heat because of our metabolism. So we have to constantly lose heat to maintain our normal temperature.
So the bigger the gradient between our body and the environment, the more rapidly we can get rid of that heat.
So when it's hot outside, our bodies sweat and increase blood flow to the skin to cool down faster.
Call us at 1-800-WHY-ISIT with your science question. If we use it, you'll get a free Science Update mug. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
This may not be a question that you've thought about, but it tells us something important about both basic physics and the way our body works. If you put a bucket of warm water outside, and that warm water just happened to be 98.6 degrees Fahrenheit, but the outdoor temperature was 85 degrees Fahrenheit, the water would cool down. That's because the outdoor temperature, while still warm, is cooler than the temperature of the water. Heat naturally flows from warmer places to cooler places. The heat's "goal" is to reach equilibrium–a state where everything is the same temperature as everything that surrounds it. That's why a hot bowl of soup or a cold glass of soda will eventually reach room temperature if you leave them out long enough.
The difference between you and a bucket of water (well, one of many differences) is that your body is constantly generating more heat. All that heat has to go somewhere, so it tries to escape through your skin. The greater the difference between the outside temperature and the temperature of your body, the faster that heat will escape. That's why you'll feel much cooler on a 60-degree day than on a 90-degree day.
The sun is another factor to consider. When meteorologists measure the temperature outside, they measure it in the shade. However, if it's 90 degrees in the shade and you're out in the sun, you're absorbing additional heat from the sun. That makes your body have to work even harder to lose enough heat to keep you comfortable.
If you were a cold-blooded animal, like a lizard, the rules would be different. These animals don't generate nearly as much internal heat as mammals do. (Generating your own body heat to maintain a constant temperature is called thermoregulation.) So if a lizard goes into the shade on an 85-degree day, its body temperature would get very close to 85 degrees. So a lizard is more like a bucket of water than you are. Isn't that nice to know?
Now try and answer these questions:
- Why do you feel warm on a 90-degree day?
- What additional challenges does your body face when the outdoor temperature goes above 98 degrees?
- Given this information, why do coats keep you warm in the winter? Why is it dangerous to wear a heavy coat on a hot day?
- Mammals that live in cold environments, like sea lions and polar bears, often have thick layers of fat or fur. How do these adaptations help them regulate their temperature?
- What are the advantages of thermoregulation?
To study heat transfer, try this online Thermodynamic Equilibrium physics experiment from the University of Oregon's Virtual Lab.
Harvard University's Division of Engineering and Applied sciences offers a primer on human thermoregulation.