This took me an embarrassingly long time to come to grips with. I've studied a good deal of physics in high school and college (not majoring in it, but somewhat related - in structural engineering). Until recently, I always thought that the process of adiabatic heating could be thought in terms of elastic collisions, where gas molecules could be simplified into 3 degrees of freedom per molecule, much like billiard balls. When I compress a piston, the translational motion of that piston wall (assuming rigid behavior) adds momentum to these molecules, heating them up. I've more recently realized that the classical analogy doesn't hold in explaining why certain gases heat up more than others when compressed. Some of the lightest gases, such as hydrogen and helium, even cool during compression in what's known as the Reverse Joule-Thomson effect. These assume processes near room temperature and far from their inversion temperature. And yet such light gases supposedly satisfy the main assumptions behind ideal gas behavior along with its Newtonian mechanics. So, the electromagnetic near-field interactions between gas particles seems more important for light gas molecules - that is, deviations from the ideal gas law - than it would be for heavier gas molecules. Hydrogen and helium have relatively low inversion temperatures, so a qualitative description of its near-room temperature behavior is that near-field repulsion tends to dominate. It's an interesting twist in how I always thought about gases (for the last 20+ years of my 36-year life!), but I wonder whether the breakdown in this grade school heuristic extends across diatomic, triatomic, and larger molecules for which behavior is known to be more electrostatically active and moreover attractive, instead of repulsive, near room temperature. What originally motivated me to think about this was thinking about how heat pumps really work - why they are more efficient for a house than an ideal furnace, i.e., creating heat energy 100% from scratch - without violating conservation of energy. Comments and thoughts appreciated.