According to the second law of thermodynamics, how does heat travel?

The second law of thermodynamics states that heat naturally flows from a region of higher temperature to a region of lower temperature. This principle is fundamental to understanding how energy transfers during thermal processes. In practical applications, it explains why warmth from your body dissipates into the cooler air in a room, or why an ice cube melts in a warm drink—heat moves from the warmer liquid to the colder ice.

This flow continues until thermal equilibrium is reached, meaning the temperatures of the two bodies become equal. Hence, the correct answer illustrates this natural tendency of heat transfer, which is a foundational concept in the study of thermodynamics and plays an essential role in HVAC systems.

The other options do not accurately reflect the behavior of heat transfer as dictated by the second law. For example, heat cannot spontaneously travel from a cooler body to a warmer body, and it does not move based on an independent mechanism isolated from temperature differences. Likewise, pressure differences do not govern heat transfer directly; instead, they pertain to fluid dynamics and thermodynamic cycles.