What is the primary characteristic of thermal energy in a substance?

Thermal energy in a substance is fundamentally linked to the kinetic energy of its particles. As a substance is heated, the particles gain energy and move more vigorously. This increased motion results in higher temperatures, which reflect an increase in the average kinetic energy of the particles. Thus, thermal energy is a reflection of the energy associated with the movement and interactions of particles within the material.

Understanding that thermal energy is tied to kinetic energy helps clarify thermal processes, such as how heating a substance leads to changes in temperature or phase. For instance, when water is heated, the increased thermal energy causes the water molecules to move faster, ultimately leading to changes from liquid to vapor during boiling.

While thermal energy can also be influenced by other factors, such as the structure of the material and its state of matter (solid, liquid, gas), the primary characteristic under consideration is the relationship between thermal energy and the kinetic energy of the particles.