Heat definitions and example sentences on Wordnik

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noun A form of energy associated with the motion of atoms or molecules and capable of being transmitted through solid and fluid media by conduction, through fluid media by convection, and through empty space by radiation.
noun The transfer of energy from one body to another as a result of a difference in temperature or a change in phase.
noun Physics The sensation or perception of such energy as warmth or hotness.

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Century Dictionary (70)

A sensation of the kind produced by close proximity to fire. The sensation of heat is commonly described as opposite in character to that of cold; but, strictly considered, this opposition lies not so much in these sensations themselves as in their causes and associations. Like cold, the sensation of heat probably resides only in special points of the skin, the points sensitive to heat being different in location from those which are sensitive to cold.
That condition of a material body which is capable of producing the sensation of heat; in physics, the corresponding specific form of energy, consisting in an agitation of the molecules of matter, and measured by the total kinetic energy of such agitation. See energy, 7. Heat is of two kinds—heat proper, resident in a body, and radiant heat, which, from the physical point of view, is not properly heat at all, but, like light, a form of wave-motion projected by the vibrations of the luminiferous ether. Heat was formerly believed to be caused by an indestructible material fluid, called caloric. It is now known to be not a substance, but the energy of molecular motion, consisting, in the case of a gas, of nearly uniform rectilinear motions, with sudden changes of direction and velocity when the molecules come near enough to one another; in the case of a liquid, of irregular wanderings of its molecules; and in the case of a solid, of orbital or oscillatory motions. This motion entirely ceases only at the absolute zero point. The temperature is in fact nothing but the amount of heat per molecule. The effects of absorbed heat upon a body are: (1) Increase of temperature—that is, increase of the heat of each molecule. To a limited extent this can be measured by the senses, but more accurately by thermometers (see thermometer), the thermopile, etc. (2) Expansion, or increase of volume (see expansion). (3) Change of state, as of a solid to a liquid (see fusion and liquefaction), or of a liquid to a gas (see vaporization). Thus, to transform ice at 0° C. into water (melt it), or water at 100° C. into vapor or steam, a large amount of heat is required. This heat disappears as sensible heat, and is said to become latent. Latent heat, however, is a misleading term, for it is not true that heat is latent as such, but only that so much heat-energy has been expended in changing the position of the molecules and overcoming their mutual attractions. If the process is reversed, this latent heat becomes sensible, as, for example, when steam is condensed in a steam-radiator. Heat also produces electrical effects (see electricity), and is instrumental in initiating chemical changes. Heat may be transmitted from one place to another—(1) By convection (see convection), when the hot body is itself moved, as in heating by hot air conveyed in flues, or by hot water carried in pipes. (2) By conduction (see conduction), where the heat travels slowly through the mass of the body, as when one end of an iron bar is thrust into the fire and the other end gradually becomes heated. In this case it is the molecular motion of the iron which is propagated. (3) By radiation (see radiation). When heat was believed to be a substance, the radiation of heat was explained, in a manner analogous to the abandoned emission theory of light (see light), as the actual transfer of the heat-fluid itself; now, however, radiant heat is known to be the energy of heat transferred to the luminiferous ether (sec ether), which fills all space and also pervades all bodies. The hot body sets the ether-particles in vibration, and this vibratory motion, in the form of waves, travels in all directions and with a velocity of about 186,000 miles per second. If this radiant heat impinges upon a body, part of it may be absorbed, or, in other words, the molecules of the body may themselves be set in motion by the ether-waves. There is no essential difference between radiant heat and light, both being forms of radiant energy (see energy), the ether-waves differing intrinsically among themselves in wave-length only, and thus producing different effects, heating, luminous, and chemical, in the bodies upon which they impinge, according to the nature of these bodies. The rays whose heating effect is generally the greatest are of greater wave-length than those which most affect the eye (light-rays), and have longer periods of vibration. Like light-rays, they may be reflected, refracted, diffracted, and polarized. The quantity of heat of a body, or the amount of heat-energy which a body gains or loses in passing through a given range of temperature, is measured in thermal units (see heat-unit)—that is, by the quantity of water which it would raise through 1° C. (or 1° F.); it is given by the product of its weight into the number expressing the range in temperature multiplied by the specific heat. In ordinary speech heat and temperature are not distinguished. See temperature. Heat is a very brisk agitation of the insensible parts of the object, which produces in us that sensation from whence we denominate the object hot: so what in our sensation is heat, in the object is nothing but motion. Locke, Elem. of Nat. Phil., xi. Since heat can be produced, it cannot be a substance; and since whenever mechanical energy is lost by friction there is a production of heat, … we conclude that heat is a form of energy. Clerk Maxwell, Matter and Motion, xciii In the strictest modern scientific language … the word heat is used to denote something communicable from one body or piece of matter to another. Sir William Thomson, Encyc. Brit., XI. 555.
In ordinary use, a sensibly high temperature, as the warmth of the sun, or of the body. Men of Nubye ben Cristene: but thei ben blake as the Mowres, for grete Hete of the Sonne. Mandeville, Travels, p. 46. Thei were sette vnder the hawethorn in the shadowe by the broke, and let theire horse pasture down the medowes while the heetc was so grete, for it was a-boute mydday. Merlin (E. E. T. S.), iii. 522. When she walketh apace for her pleasure, or to catch her a heate in the colde mornings. Puttenham, Arte of Eng. Poesie, p. 248.

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The energy remained as long as the heat was applied. — ERE.net
These Somalia pirates don't like to go too afar from safe harbor, without a place to beat a hasty retreat to if the heat is applied to them they wouldn't stand much of a chance. — Democratic National Committee
The refrigerant evaporates as the heat is absorbed, becoming a gas. — The Latest on Air America
For a summer wedding, how well the flowers will stand up to the heat is a very important consideration. — xml's Blinklist.com
Ironically, the heat is a defense mechanism, designed to keep animals from destroying the plants. — Hungry Magazine

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