Thermal energy is defined as which quantity belonging to a substance's particles?

1. Thermal energy is defined as the average kinetic energy of the particles, molecules or atoms, making up a substance. 2. Potential energy between particles contributes to internal energy but is not what thermal energy measures. 3. Thermal energy is an average across all particles, not the peak kinetic energy of a single particle. 4. Particle mass on its own says nothing about motion, so it cannot define thermal energy. 5. The average kinetic energy description is therefore correct. _Source: OpenStax Physics (CC BY 4.0), Ch 11 "Thermal Energy, Heat, and Work", section 11.1 Temperature and Thermal Energy_