| Themes > Science > Physics > About Physics, Generalities > A Brief History and Philosophy of Physics > The Development of Classical Physics: Mechanics, Heat, Optics, Electromagnetism, Atoms > Thermal Physics |
The invention of a practical steam engine by Thomas Newcomen (1663-1729) prompted great scientific interest in the study of heat, and was a major contribution to the industrial revolution which began in England in the mid 18th century. (It is ironic that the industrial revolution, which began to apply scientific principles to the production of goods as predicted by Bacon one hundred years earlier, also led to the virtual slave labour of children and the poor in mines and factories.) Sadi Carnot (1796-1832), a French engineer, laid the basis for our understanding of heat engines (any engine which uses heat to produce power, such as the automobile engine, or a coal or nuclear electrical power station). He compared the operation of a heat engine with that of a waterwheel, with heat "falling" from a higher to a lower temperature. Joseph Black (1728-99), the professor of medicine at Glasgow University, began to quantify heat by the measurement of the specific heat capacities (the amount of heat required to raise the temperature of a given mass by one degree) of different substances, compared to that of water. Motivated by the heat generated in the boring of cannons, Count Rumford (1753-1814), first showed that heat could be produced in limitless quantities by friction, and so was not a material substance (caloric) as had been believed previously. James Prescott Joule (1818-89), by rotating a "paddle wheel" under water and measuring the increase of temperature, established a numerical equivalence between work and heat. He also showed that the heat produced by an electrical current I in a wire of resistance R was given by I2R, a relationship now known as Joule's law. Joule's quantitative work on the interconversion of energy laid the basis for the first law of thermodynamics, which says that the change in the energy of a system is equal to the heat input to it plus the mechanical work done on it. This law was first stated explicitly by the German Rudolph Clausius and Englishman William Thomas Kelvin in 1851. Clausius also realized that a heat engine could utilize only some of the available heat to do work, and from this developed the concept of entropy, the quantity of heat transferred divided by the temperature. Clausius showed that the entropy always increased in any spontaneous natural process, and so established the second law of thermodynamics. As with Newton's three laws, the laws of thermodynamics form the foundation for the understanding of thermal physics. |
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