What does temperature measure in a substance?

Temperature measures the average kinetic energy of the molecules in a substance. When a substance is heated, its molecules move faster, resulting in a higher temperature. Conversely, as the substance cools, the movement of its molecules slows down, leading to a lower temperature. This relationship indicates that temperature is a direct reflection of the motion and activity level of microscopic particles within the material.

Total thermal energy, molecular density, and specific heat capacity relate to other thermal properties of substances but do not directly define temperature. Total thermal energy incorporates both the average kinetic energy and potential energy of all the molecules in a substance. Molecular density refers to how closely packed the molecules are and does not relate to the energetic aspect of temperature. Specific heat capacity is a material property that indicates how much energy is needed to raise the temperature of a substance and is influenced by temperature but does not define it. Therefore, understanding temperature as a measure of average kinetic energy is key to comprehending how heat and energy affect substances in HVAC systems.