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Unformatted text preview: Chapter 1 Introduction Read BS, Chapter 1 1.1 Preliminary semantics We introduce here classical thermodynamics . The word “thermo-dynamic,” used first by Thomson (later Lord Kelvin), 1 has Greek origin, and is translated 2 as the combination of • θ ´ ǫρμη , therme : heat, and • δ ´ υναμις , dynamis : power. An image of Thomson and his 1849 first use of the word is given in Fig. 1.1. Figure 1.1: William Thomson (Lord Kelvin) (1824-1907), Ulster-born Scottish scientist; im- age from http://www-history.mcs.st-and.ac.uk/ ∼ history/Biographies/Thomson.html and image giving the first use of “thermo-dynamic” extracted from his 1849 work. 1 W. Thomson (later Kelvin), 1849, “An account of Carnot’s theory of the motive power of heat; with numerical results deduced from Regnault’s experiments on steam,” Transactions of the Royal Society of Edinburgh , 16:541-574. See also C. W. Smith, 1977, “William Thomson and the creation of thermodynamics: 1840-1855,” Archive for History of Exact Sciences , 16(3): 231-288. 2 All Greek spellings and etymologies are drawn from the Oxford English Dictionary , 2nd edition, 1989. 9 10 CHAPTER 1. INTRODUCTION The modifier “classical” is used to connote a description in which quantum mechanical effects, the molecular nature of matter, and the statistical nature of molecular behavior are not considered in any detail. These effects will not be completely ignored; however, they will be lumped into simple averaged models which are valid on the macroscale. As an example, for ordinary gases, our classical thermodynamics will be valid for systems whose characteristic length scale is larger than the mean free path between molecular collisions. For air at atmospheric density, this about 0 . 1 μm (1 μm = 10 − 6 m ). Additionally, “classical” also connotes a description in which the effects of finite time- dependency are ignored. In this sense, thermodynamics resembles the field of statics from Newtonian mechanics. Recall Newton’s second law of motion, m d 2 x /dt 2 = ∑ F , where m is the mass, x is the position vector, t is time, and F is the force vector. In the statics limit where ∑ F = , inertial effects are ignored, as is time-dependency. Now a Newtonian would consider dynamics to imply motion, and so would consider thermodynamics to imply the time-dependent motion of heat. So a Newtonian would be more inclined to call the subject of these notes “thermostatics.” However, if we return to the earlier Greek translation of dynamics as power, we are actually truer to the classical connotation of thermodynamics. For the fundamental interplay of thermodynamics is that between so-called thermal energy (as might be thought of when considering heat) and mechanical energy (as might be thought of when considering power, a work rate). More formally, adopting the language of BS (p. 13), we will take the definition • thermodynamics : the science that deals with heat and work and those properties of...
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This note was uploaded on 03/02/2012 for the course THERMO 20231 taught by Professor Powers during the Spring '10 term at Notre Dame.
- Spring '10
- The Land