![]() The joule is named for James Prescott Joule (1818 - 1889), who studied the relation between mechanical and heat energy discovered earlier by count Rumford. One calorie of heat is the equivalent of 4.186 J. The joule is also used to measure thermal energy. The amount of energy delivered by a one watt source of power in one second is one Joule. One joule measures the energy released by a electric charge of one coulomb dropping one volt in absolute value of electrical potential. One may also use electric units to define the joule. 'Joule' is variously pronounced 'jool' (rhymes with 'jewel') or 'joul' (rhymes with 'jowl'). It follows that J (joule) is expressed in SI basic units as: The mechanical quantities involved have the SI units: One newton equals a force that produces an acceleration of one meter per second (s) per second on a one kilogram (kg) mass. One joule equals the work done (or energy expended) by a force of one newton (N) acting over a distance of one meter (m). All rights reserved.The joule (symbol J) is the SI unit of energy-a measure of the capacity to do work or generate heat. Copyright © 2023, Columbia University Press. The Columbia Electronic Encyclopedia, 6th ed. The heat of vaporization, or latent heat of vaporization, is the heat that must be added to convert one unit of mass of the substance from a liquid to a gas. During the liquid-gas transition, the temperature remains constant until the change is completed. The latent heat of fusion for the ice-to-water transition is 80 calories per gram.Īfter a substance is completely changed from a solid to a liquid, further addition of heat again causes the temperature to rise until it reaches the boiling point, the particular temperature at which the given substance changes from a liquid to a gas. Like specific heat, latent heat is also a property of the particular substance. The amount of heat needed to convert one unit of mass of a substance from a solid to liquid is called the heat of fusion, or latent heat of fusion, of the substance. All of the heat being added is being converted to the internal potential energy associated with the liquid state. While the solid-liquid transition is taking place, there is no change in temperature. This temperature is a particular property of the substance and is called its melting point. When a solid reaches a certain temperature, it changes to a liquid. For example, the specific heat of water is 1 calorie per gram per degree Celsius i.e., 1 calorie of heat is needed to raise the temperature of 1 gram of water by 1 degree Celsius it is also 1 Btu per pound per degree Fahrenheit. Because of the way in which the calorie and the Btu are defined, the specific heat of any substance is the same in either system of measurement. ![]() ![]() The amount of heat needed to raise a unit of mass of the substance one degree of temperature is called the specific heat of the substance. Scientists express heat in terms of the joule, a unit used for all forms of energy.Īs heat is added to a substance in the solid state, the molecules of the substance gain kinetic energy and the temperature of the substance rises. Heat is commonly expressed in either of two units: the calorie, an older metric unit, and the British thermal unit (Btu), an English unit commonly used in the United States. ![]() Temperature is a measure of the average translational kinetic energy of the molecules of a system. ![]()
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