On the work of internal forces

TL;DR

This paper explores the significance of internal forces and their work in changing a system's energy across mechanics, thermodynamics, and electromagnetism, emphasizing their importance in education.

Contribution

It highlights the role of internal forces in energy variation and advocates for their explicit consideration in teaching physics.

Findings

Internal work affects system energy in various physical contexts.

Internal energy variations should be explicitly taught alongside other energy changes.

The paper provides examples from mechanics, thermodynamics, and electromagnetism.

Abstract

We discuss the role of the internal forces and how their work changes the energy of a system. We illustrate the contribution of the internal work to the variation of the system's energy, using a pure mechanical example, a thermodynamical system and an example from electromagnetism. We emphasize that internal energy variations related to the work of the internal forces should be pinpointed in the classroom and placed on the same footing as other internal energy variations such as those caused by temperature changes or by chemical reactions.