What is the process called when thermal energy flows from a higher temperature to a lower temperature?

The process where thermal energy flows from a higher temperature to a lower temperature is known as heat transfer. This fundamental concept in thermodynamics describes how energy in the form of heat moves between objects or within an object due to a temperature difference. Heat transfer occurs through three primary methods: conduction, convection, and radiation.

In conduction, heat is transferred through direct contact between materials, while convection involves the movement of fluids (liquids and gases) carrying heat with them. Radiation, on the other hand, involves the transfer of heat in the form of electromagnetic waves, such as infrared radiation, and does not require a medium to occur.

The movement of heat continues until thermal equilibrium is reached, at which point the temperatures of the two objects become equal. Understanding heat transfer is essential for many scientific applications, including engineering, climate science, and everyday phenomena.

The other processes mentioned, such as thermal expansion, refer to changes in the size or volume of substances as a result of temperature changes, rather than the flow of thermal energy. Heat radiation specifically describes the type of heat transfer that occurs via electromagnetic waves, and temperature equilibrium is the state of balance where there is no net flow of heat between objects, rather than the process of heat transfer itself.