Curious Nature: How do our bodies gain and lose heat when the temps drop? (column)
According to the laws of physics, cold doesn’t exist. It’s simply the absence of heat. But that’s not entirely comforting to someone who is suffering from the cold. Humans have a fairly wide range of diversity in terms of cold tolerance, but ultimately, like most things in life, it comes down to science.
There are numerous factors that influence how fast our bodies gain or lose heat. Heat is transferred because of a temperature differential, or a difference in the amount of energy between two objects or systems. The laws of thermodynamics come into play here, as systems try to reach a thermal equilibrium, where the energy is evenly distributed and there is no net heat transfer between them. But when one object has a greater temperature (average heat content) than another, the heat is transferred from the warmer object to the colder one.
It doesn’t matter what kind of heat we are talking about. It might be your body heat or the body heat of a small mammal. But heat is heat, and it is gained or lost through three primary mechanisms: conduction, convection and radiation. Having a greater understanding of how heat is lost through each of these methods can make us all warmer and safer out there. For the sake of space, we’ll focus on how heat is lost, but keep in mind that we can gain heat, too, through exercise or by eating hot food, for example.
Radiation is probably the most misunderstood form of heat loss, and often the most difficult to prevent, because objects are always radiating heat to its surroundings. Radiation is the transfer of heat by electromagnetic waves, and it is the only form of heat transfer that can occur in a vacuum, meaning it doesn’t require matter. This is how we get heat from the sun, as it travels in waves through the vacuum of space, reaching our planet approximately 8 minutes and 20 seconds after it leaves our life-giving star.
Conduction, on the other hand, is more concrete, and it occurs when two solids touch directly and vibrating molecules transfer heat directly over the differential. This is what happens when you sit on the cold chairlift seat and heat is transferred from your warm derriere to the cold metal beneath you. Be thankful for those padded cushions, which insulate and slow down this loss of heat. But if you sit long enough, the nonexistent cold will win.
Convection, on the other hand, occurs in fluids, which includes liquids and gases. This is the type of heat transfer that occurs when the wind blows or when you enter a body of water. Imagine your body constantly radiating heat to the surrounding air (or water), and as the fluid circulates, the heat is whisked away and replaced by new, colder fluid, and the cycle repeats. This is part of the reason why falling into cold water can be so dangerous. This danger is magnified by the heat loss or gain that occurs during phase changes. So if you are wet, then the evaporating water saps even more heat from your body.
There’s more to this lesson, of course, and the more you understand about how heat is gained and lost by the human body, the more comfortable you will be in the outdoors. You can learn more about the science of keeping warm at Walking Mountains Science Center’s upcoming snowshoe series in partnership with Icebreaker. Visit http://www.walkingmountains.org for more information.
Jaymee Squires is the director of graduate programs at Walking Mountains Science Center. Squires doesn’t like to be cold, so if you see her out, then you can be sure she will be layered up and prepared for anything.