Construction of Thermodynamic Models for Elementary Teaching

Abstract

The author has found great value in the use of solid models in freshman physics teaching to illustrate (1) the law of ideal gases, and (2) the van der Waals equation of state and the behaviors of vapors and liquids. Many freshman students have difficulty in visualizing the shape of the thermodynamic surfaces from, let us say, a blackboard sketch of a set of isotherms, and the better part of a precious lecture hour may be consumed in explaining, with many words, what would be almost obvious if one had a solid model in his hands. The author has found that more than half of a class of average intelligence, having learned that an ideal gas is described by the equation PV=NRT, will be sorely puzzled by the adiabatic equation for ideal gases, PVγ=const. It helps these puzzled students surprisingly little to be told that, since the first equation contains three variables, it is not inconsistent with the second. With many of them, however, the matter becomes clear when they are shown an ideal gas surface on which have been plotted isotherms, adiabatics, and so forth.