Temperature, Thermal Energy, and the Kelvin Scale

Temperature is one of the most familiar quantities in everyday life, yet defining it precisely requires care. In physics, temperature is a measure of the average random kinetic energy of the particles that make up a substance. When we say a cup of coffee is "hot," we mean that its molecules are, on average, moving and vibrating more energetically than the molecules in a "cold" drink. Temperature does not tell us about the total energy stored in an object, only about the average energy per particle. This distinction is crucial and separates temperature from thermal energy.

Thermal energy is the energy that flows spontaneously from a region of higher temperature to a region of lower temperature. When you place a warm object next to a cold one, energy is transferred from warm to cold until bo