Chapter 24

How does Heat travel from Cold to Warm?

In chapters 16 and 17 I described my measurements from 2002, which for columns of air and water showed a vertical temperature gradient, cold at the top and warm at the bottom. In my “Pittsburgh experience” I, for the first time, calculated the magnitude of this gradient by converting the potential energy of the “dancing” molecules into a temperature increase based on their specific heat - recounted in Chapter 14. This seemed to me to be the maximum possible and explainable temperature increase. I expected my test results to show a somewhat smaller value, because, there always would be some heat loss to the environment. Certainly higher values could happen, but only for a short time, based on the temperature fluctuations of the environment, and not as a long term average.

The trouble was that I measured considerable bigger long term average values for the temperature gradient than predicted by calculation. The measured values were 5 times higher for air and 18 times larger for water Progressing in my experiments and in my thoughts step by step through the years, I only recently found a solution for this discrepancy: My calculation first written down in my “Pittsburgh experience” was basically correct, but incomplete. Correct was the first part:

”Any vertically falling molecule would fall, between collisions with other molecules under the influence of gravity, with the speed first given by Newton as the free fall speed.”

But the insight was missing:

“Under free fall conditions gravity affects only one degree of freedom, namely only the vertical component of the speed.”