Why do things expand on heating? A discussion on the need for asymmetric potentials to understand thermal expansion

Abstract Understanding thermal expansion is pivotal in various contexts such as comprehending sea level rise due to climate change. Considering the importance of these topics for physics education, this article aims to clarify the characteristics of the models used to represent and explain thermal expansion. Limitations of the linear expansion equation commonly found in textbooks are shown, emphasising the importance of conceptual discussion about thermal expansion. Microscopic models are also explored, demonstrating the inadequacy of the harmonic oscillator model in explaining thermal expansion and introducing the necessity of employing asymmetric potentials. Through the graphic of the Lennard-Jones potential and an algebraic deduction akin to Enrico Fermi’s approach, the thermal expansion of solids and its relation with asymmetric interactions is explored.