Last week I shared a list of simple tips for keeping warm while camping. A friend of mine had a bunch of questions, which led to a conversation about how outdoor gear keeps you warm. In order to understand how to pick the best gear for staying warm, we have to answer a question: how do we get cold? This post discusses just that: The Science of Cold.
The Science of Cold
Your body is kept warm by the heat that is released when you digest food. It’s like you have your own little engine. That process occurs almost continuously. If your body was completely sealed, you would eventually overheat. Fortunately, your skin and your lungs work to regulate the temperature inside your body by dumping excess heat into the atmosphere. Heat energy always moves from warm to cold. The difference between the temperature inside your body and the temperature outside sets the rate at which you give off excess heat. If your metabolism generates heat faster than you can get rid of it, you feel too warm. On the other hand, if you dump heat into the environment faster than you can replace it, you will feel cold.
Heat transfers out of your body in three different ways. Conduction is a process by which your body gives off heat to objects you’re in contact with. In convection, your body is cooled by moving air. Finally, your body is always radiating a certain amount of heat into the environment.
Conduction is a process by which heat energy moves directly from one object to another object that it is in contact with. Conduction happens very quickly through solids and liquids. If you’re touching a solid or liquid that is cooler than you are, you will start to warm it up. Heat will keep transferring out of your body and into the object until you and the object are the same temperature.
Convection is a process by which moving air cools an object. If the air around your body is cooler than you are, you will start to heat that air up. As the air heats, it will rise and cooler air will take its place. This process is usually slow because air will only move away from your body as quickly as you can heat it up. Wind speeds convection by moving air at a rate than you can heat it. If you’re wet, moisture that evaporates will help to carry heat away from your body in the same way air does.
Have you ever felt the warmth of the sun on your face? That is radiation. Any object that has heat constantly loses some heat in the form of radiation. Radiated heat moves freely through air. When radiated heat strikes a solid object, it is either reflected or absorbed.
Knowing is Only Half the Battle
Now we know that we feel cold when our bodies lose heat faster than it can be replaced. We’ve discussed the three ways that our bodies lose heat to the environment. Through conduction, we give off heat to solids or liquids that we’re in contact with. Convection is when heat is carried away from us by air or vapor. Everything in the universe that has heat constantly gives some of that heat off as radiation. Unfortunately, knowing the problem is only half the battle.
Look back soon for “The Science of Warm.”