Ch 7, p 1
(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
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
, and the law of conservation of energy is often called the
first law of
.* These laws of thermodynamics have no known exceptions and are among the most general scientific
* [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