thermo - Art Hobson, Physics: Concepts & Connections Ch...

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Ch 7, p 1 Thermodynamics (excerpts from Art Hobson, chapter 7 of the third edition, not yet published of Physics: Concepts and Connections Places with funny Arial type are changes G.S. made to fit with UPI, and sometimes I deleted parts of sentences that referred to other places in his text. Many times I have been present at gatherings of people who. ..are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is about the scientific equivalent of: “Have you read a work of Shakespeare’s?” C. P. SNOW, BRITISH SCIENTIST AND AUTHOR If you glance back at the work energy diagrams we drew for a lot of processes, or the discussions we had about friction, or any of that , you get the impression that the energy that goes into many processes eventually turns into thermal energy. This tendency of nonthermal forms of energy to end up as thermal energy is an important general feature of the universe, known as the second law of thermodynamics . It is our focus in this chapter. The big breakthrough in understanding energy was the discovery that heat (thermal energy) is actually a form of energy, in other words that heat can do work and can be created by doing work, just as can other forms of energy. This breakthrough established the validity of the law of conservation of energy even in processes involving thermal energy, and, in fact, in every known natural process. Because of the central role of thermal energy in understanding the general principles of energy, the study of energy is called thermodynamics , and the law of conservation of energy is often called the first law of thermodynamics .* These laws of thermodynamics have no known exceptions and are among the most general scientific principles known. ________________________________________ * [FOOTNOTE] More precisely, the first law of thermodynamics states that the work done on a system, plus the heating (Section 7.1) done on it, must equal the total energy increase of the system. Since heating is a thermal energy flow, the first law is really just the work-energy form (Section 6.5) of the law of conservation of energy, modified to include thermal energy flows to the system. There are three different ways of stating the second law. In its most straightforward form, it is a familiar observation about thermal energy flow (Section 7.1). Like many everyday observations, this one has profound consequences. Section 7.2 discusses one of these, namely, another form of the second law that highlights the special nature of thermal energy. Unlike other energy forms, there is a restriction on the transformations of thermal energy: It can be transformed into other forms only with limited efficiency. This leads to discussion of a device that is central to society’s use of energy: the heat engine (Sections
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This note was uploaded on 05/04/2008 for the course PHYS 2054 taught by Professor Stewart during the Spring '08 term at Arkansas.

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thermo - Art Hobson, Physics: Concepts & Connections Ch...

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