Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic constituents.
Heat flow from a high to a low temperature body occurs spontaneously. This flow of energy can be harnessed and partially converted into useful work by means of a heat engine. The second law of thermodynamics prohibits heat flow from a low to a high temperature body, but with the aid of a heat pump external work can be used to transport energy from low to the high temperature.
In ordinary language, heat has a diversity of meanings, including temperature. In physics, “heat” is by definition a transfer of energy and is always associated with a process of some kind. “Heat” is used interchangeably with “heat flow” and “heat transfer”. Heat transfer can occur in a variety of ways: by…