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38480 results in Cambridge Textbooks

Page 1138 of 1924

  • 2 - Energy

  • William C. Reynolds, Piero Colonna, Technische Universiteit Delft, The Netherlands
  • Book:
    Thermodynamics
    Published online:
    15 June 2019
    Print publication:
    20 September 2018, pp 16-31

  • Summary

    In the first chapter we reviewed the concept of energy as it arises in mechanical systems. We interpreted work as a transfer of energy and used this idea to develop expressions for kinetic and potential energy. These were special instances of the general concept of energy, which is perhaps the most fundamental concept in all of science. In thermodynamics, another relevant mode of energy transfer is heat. Once all these concepts are clear, they can be used together with the first law to analyze and design an infinite variety of systems and devices, which are at the foundation of current and future societies.

    Concept of Energy

    The Energy Hypothesis

    The ideas inherent in the general concept of energy are encapsulated in what we call the Energy Hypothesis:

    Matter can be treated as having a property, called energy, that is an extensive, conserved scalar measuring its ability to cause change; work is a transfer of energy.

    The terms used above are very important:

  • • extensive means that the energy of a system is the sum of the energies of its parts;

  • • conserved means that the total amount of energy in an isolated system does not change;

  • • scalar means that energy is a quantity without directional (vector) character;

  • • work is a transfer of energy; it provides the key to the quantitative evaluation of the energy contained by matter.

    • In Section 1.4 we used these ideas to obtain expressions for the kinetic and potential energy of matter. Other energy forms are evaluated in the same way. Since the energy hypothesis is itself used in the evaluation and measurement of the energy of matter, it is not possible to test the hypothesis of energy conservation by experimental measurements of energy. However, one can use the energy hypothesis to predict how matter will behave, and these predictions (when done correctly!) are always confirmed by experiment. Countless working devices, designed using energy analysis, provide enormous evidence of the validity and utility of the energy hypothesis. Believe in the concept of energy; it works!

    Microscopic Energy Modes

    A macroscopic quantity of matter contains a huge number of molecules, and its energy is the sum of the individual energies of all these molecules. Molecules and systems of molecules can have energy in a variety of different microscopic modes.

  • Remembering Bill Reynolds

  • William C. Reynolds, Piero Colonna, Technische Universiteit Delft, The Netherlands
  • Book:
    Thermodynamics
    Published online:
    15 June 2019
    Print publication:
    20 September 2018, pp xx-xx

  • Summary

    I started to work at this book in a very emotional situation, and those strong feelings accompanied me during the time I dedicated to its writing since then.

    Professor Bill Reynolds, whom I first met in 1994 as my mentor while pursuing a Masters degree at Stanford University, contacted me in June 2003 and told me of the new thermodynamics textbook he had started to write some time before. He mentioned that he had health problems. He then asked me if I wanted to visit him before the end of the year to talk about the book. I had been spending periods at Stanford working with him since I graduated there in 1995. As always, I enthusiastically accepted the invitation and arrived at Stanford in November of 2003. The moment I met Bill in his office I understood that something was not quite right.

    After a very short preamble, he told me “You remember our plan to work together on a new thermo book and to add your material on properties of mixtures, energy systems, and the rest? Well, I would like you to pick up from where I am leaving this book and finish it, as I am going to die soon of a brain tumor.” I was shocked and immensely sad, and at the same time I felt honored and committed. Those last days I spent with him were extremely intense and moving. We only managed to exchange ideas about the book very briefly, as his health was rapidly deteriorating.

    I will never forget the moment I parted from him. I was standing next to his bed in his home, holding his hand, with my eyes full of tears, in silence, while I was mentally thanking him for all he had done for my education. He was looking back at me, with tenderness. It was December 26th, 2003. Bill died on January 3rd, 2004.

    I had become involved with this book earlier, during my Masters studies at Stanford. I was taking ME270-Engineering Thermodynamics, taught by Bill.

    He was the most extraordinary lecturer, as anybody who has ever followed one of his classes can testify. Meanwhile, I was one of his research assistants, working on thermodynamic property models for multicomponent fluids.

Page 1138 of 1924