Instructors_Guide_Ch16 - 16 A Macroscopic Description of...

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16 A Macroscopic Description of Matter Recommended class days: 2 Background Information The four chapters of Part IV continue the development of the concept of energy, now focusing on the transfer and transformation of energy in macroscopic systems. You should urge students to review Chapter 11 because the present development picks up where that chapter left off. Note that pressure is introduced in Chapter 15; hence, Sections 15.1–15.3 are a prerequisite for Part IV even if you don’t cover the rest of Chapter 15. Of all the major subjects in introductory physics, thermal physics looks most like a potpourri of unrelated ideas and equations. Students—and even many instructors—find little logic or coherence in the conventional presentation of thermal physics. A major goal of this textbook is to simplify and streamline the presentation so that the logic of thermodynamics is clear. The primary message to students has three main ideas: Thermal physics is concerned with understanding the properties of macroscopic systems. Macroscopic systems are characterized by a small number of “state variables.” • Macroscopic state variables are related to the microscopic motion of the atoms in the system. Consequently, we can infer atomic information from macroscopic measurements. Thermodynamics is a more general study of how macroscopic systems transform and use energy. To keep this development free of distractions, a few traditional topics (e.g., temperature scales, thermal expansion, and the details of heat transfer) have been omitted or greatly abbreviated. These are topics that students can easily learn in other courses if they are needed for their major. It must be acknowledged that thermal physics is plagued with many inconsistent sets of units. As much as we might wish otherwise, all these many non-SI units are widely used throughout science and engineering. There’s no point in trying to shield students from this harsh reality, so this textbook presents examples and problems in many different units of pressure, volume, temperature, mass, and so on. Not surprisingly, one of the most common student errors is failure to convert to the proper units for doing calculations. Instructors are urged to be very explicit about units and conversions while working example problems. The measurement of volume is particularly telling. A significant fraction of students in most introductory physics classes cannot convert cm 2 to m 2 or cm 3 to m 3 . Because 1 m = 100 cm, you’ll find many students using 1 m 2 = 100 cm 2 and 1 m 3 = 100 cm 3 . Simply telling them the conversion factor has little effect, but you can quickly convince most of them with a simple exercise of computing the number of 1 cm × 1 cm × 1 cm cubes in a 1 m × 1 m × 1 m cube. The McDermott group at the University of Washington has done limited research on student
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Instructors_Guide_Ch16 - 16 A Macroscopic Description of...

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