What does temperature measure in a substance?

Temperature is defined as a measure of the average kinetic energy of the particles in a substance. As temperature increases, the particles move more vigorously, meaning their kinetic energy rises. This relationship is fundamental to understanding how temperature correlates with the behavior of matter, including the phase changes that substances undergo when heat is added or removed.

In contrast, other concepts like total energy content or potential energy do not directly measure temperature. Total energy would include both kinetic energy (due to temperature) and potential energy, while potential energy alone does not reflect the temperature of a substance. Additionally, while phase changes do relate to temperature, they describe a state of matter rather than a direct measure of the kinetic energy of particles within that state. Thus, the correct answer reflects the relationship between temperature and the motion of particles in a substance, which is accurately captured by average kinetic energy.