Microscopic Origin of Heat
Heat characterizes macroscopic systems and processes, but like other thermodynamic quantities it has a fundamental origin in statistical mechanics — the physics of the underlying microscopic degrees of freedom.
For example, within a range of temperature set by quantum effects, the temperature of a gas is proportional (via Boltzmann's constant kB) to the average kinetic energy of its molecules. Heat transfer between a low and high temperature gas brought into contact arises due to the exchange of kinetic and potential energy in molecular collisions. As more and more molecules undergo collisions, their kinetic energy equilibrates to a distribution that corresponds to an intermediate temperature somewhere between the low and high initial temperatures of the two gases. An early and vague expression of this was by Francis Bacon. Precise and detailed versions of it were developed in the nineteenth century.
For solids, conduction of heat occurs through collective motions of microscopic particles, such as phonons, or through the motion of mobile particles like conduction band electrons. As these excitations move around inside the solid and interact with it and each other, they transfer energy from higher to lower temperature regions, eventually leading to thermal equilibrium.
Read more about this topic: Heat
Famous quotes containing the words microscopic, origin and/or heat:
“The television screen, so unlike the movie screen, sharply reduced human beings, revealed them as small, trivial, flat, in two banal dimensions, drained of color. Wasn’t there something reassuring about it!—that human beings were in fact merely images of a kind registered in one another’s eyes and brains, phenomena composed of microscopic flickering dots like atoms. They were atoms—nothing more. A quick switch of the dial and they disappeared and who could lament the loss?”
—Joyce Carol Oates (b. 1938)
“The real, then, is that which, sooner or later, information and reasoning would finally result in, and which is therefore independent of the vagaries of me and you. Thus, the very origin of the conception of reality shows that this conception essentially involves the notion of a COMMUNITY, without definite limits, and capable of a definite increase of knowledge.”
—Charles Sanders Peirce (1839–1914)
“... often in the heat of noonday, leaning on a hoe, looking across valleys at the mountains, so blue, so close, my only conscious thought was, “How can I ever get away from here? How can I get to where they have books, where I can be educated?” I worked hard, always waiting for something to happen to change things. There came a time when I knew I must make them happen; that no one would do anything about it for me. And I did.”
—Belinda Jelliffe (1892–1979)