Back in the Common Science introduction, I told you that part of my inspiration for writing this blog are the conversations I had with friends and relatives over the years. Back in college I had a debate with an old girlfriend that I thought you might enjoy. Like many questions I have gotten over the years, it began with “OK, Mr. Engineer …..” I have never been sure whether it is my personality or just my degree that have provoked the “stump the engineer” questions.
So her question was “OK, Mr. Engineer, how come metal is colder than everything else?” My answer was “It’s not.” Her response was “Of course, it is, you have to be wrong”.
So I started on my explanation. I said that if we were going to discuss whether or not one thing was colder than the other, we first had to agree on a definition of “colder”. So we agreed, or at least I thought we did, that colder meant lower temperature. So then we had to agree on the definition of temperature. (I know what you are thinking, but yes I really did have a girlfriend in college, several in fact!).
Temperature is defined as the average kinetic energy of molecules of the item in question. Molecules can hold kinetic energy through translation (moving around), vibrating, and rotating. So a molecule at high temperature is moving, vibrating, and rotating very quickly. As the temperature is reduced the moving, vibrating, and rotating slow down. In fact, the definition of absolute zero on the temperature scale is when all moving, vibrating, and rotating stop.
So our conversation moved to the example of two chairs sitting in a freezer, one made of wood and other one of metal. My girlfriend’s position was that when you pulled the two chairs out of the freezer that the metal one was colder. I confidently, and correctly, informed her that she was wrong. That, in fact, when removed from the freezer the average kinetic energy and, therefore, the temperature of the two chairs were the same.
She told me that I had to be wrong because if you pulled the two chairs out of the freezer you could absolutely, and without a doubt, feel that the metal chair was colder. Like a good engineer I informed her that she was confusing heat transfer rate with temperature. That the metal chair was not colder than the wooden chair it was simply more effective in transporting heat away from your body than the wooden chair.
I proceeded with an explanation of heat transfer, how it worked and why it was not even remotely synonymous with temperature. I used what I believed to be useful and enlightening, comparison between heat and electrical conduction, to make this clearer. She listened politely with an increasingly bemused look on her face.
When I finished my explanation I was most pleased with myself. She smiled and me and pronounced, “See I was right, the metal chair is colder.” We broke up soon thereafter.
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