\def\thetitle{Knight Physics}
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{\huge\bf\thetitle}\\
\em\large{}John Denker
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Here are some notes concerning the book
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Randall D.~Knight \\%%
\book{Physics for Scientists and Engineers} \\%%
%% John Wiley \& Sons (2011)
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This is just a collection of notes that I have accumulated. It should
not be considered a book review. It is not by any means complete.
Perhaps gradually it will become more complete and more balanced.
\tableofcontents
\section{Some Observations}
\label{sec-misc}
\begin{description}
\xitem{agent} On page 117 it asks, \ Among other
things, it says \ It insists on
distinguishing the roles of the agent \
from the object that is acted upon by the force.
This violates the letter and spirit of the third law. A force is just
a force. It is not just unnecessary but actively misleading to
introduce the notion of \.
\xitem{anchored-force} On page 118 it calls for drawing force
vectors with the tail of the vector anchored on the particle.
First of all, this embodies a fundamental misconception
about vectors. In reality, a vector has a direction and
magnitude; it does not have a direction, magnitude, and
location.
Secondly, you get into all sorts of trouble if you insist on anchoring
vectors by their tails. Sometimes it is better to anchor them by
their middles, or to move them somewhere else entirely.
\xitem{inertial} On page 129, it defines and describes an \. It then illustrates this with an example that contradicts
everything that has been said. In accordance with Einstein's
principle of equivalence, the only difference between Figure 5.21(a)
and 5.21(b) is a different value of $g$. Either both frames are
valid, or neither is.
\xitem{fake-traction} On page 181, the traction setup is fake and
impractical.
\xitem{conserved-always} On page 219, it says that momentum is
conserved \.
That is a terrible thing to say. In fact, momentum is conserved,
period.
\xitem{bernoulli-energy} On page 407, it says Bernoulli's
equation is \.
In fact, though, all fluids are compressible to some extent, and when
we take that into account, we find that Bernoulli's equation has more
to do with \jem{enthalpy} than energy.
\xitem{bernoulli-strip} On page 427, it suggests blowing across the
top of a strip of paper, to demonstrate Bernoulli's principle. This
is, alas, demonstrates nothing of the sort.
%% FIXME: link to reference.
\xitem{random-thermal-energy} On page 477, it says \
Authors should be allowed to define their terms however they like,
within reason, but this is unreasonable. To the extent that \ can be defined at all, it needs to include the potential
energy as well as the kinetic energy of the atoms and molecules. In a
solid, half the heat capacity comes from potential energy, and half
from kinetic energy.
\xitem{def-heat} On page 477, definition of \.
\eat {
On page 477, the \<\graylight{stop to think 17.3}\> box throws a harsh
light on this issue, because the answer to several of the questions
could go either way, yes or no, depending on which definition of
\ you use.
}
\xitem{def-entropy} On page 518, it says \
Gaaack!
\xitem{one-kind-of-charge} On page 720, it introduces the idea
of electric charge by saying \
There are definitely not two kinds of charge. If there were, we would
need two variables: one to keep track of the ``resinous electricity''
and another to keep track of the ``vitreous electricity\qq. In fact,
we keep track of a single charge variable, which can be positive or
negative. For details on this, see \jreference{one-kind-of-charge}.
This was figured out by Watson (1747) and independently by Franklin
(1747). Indeed, Franklin introduced the terms ``positive\qq,
``negative\qq, and ``charge'' for precisely this reason, to indicate a
surplus or a deficit of the \jem{one} type of electricity. See
\jreference{subatomic}.
\xitem{v-pot} All of chapter 29 assumes the voltage is a potential.
\xitem{good-potentials} On page 826, figure 28.27 shows four ways of
visualizing the $1/r$ potential. This is a good thing in principle.
However, the contour map is not quite right. The $V=1$ and $V=3$
contours are to scale; so far so good. However, the contour in
between surely must represent $V=2$, but its radius is not what it
should be. It should be half as big as the $V=1$ contour. Why not
just compute all the contours quantitatively, as in \jfigure
{equipot-inverse-r}?
Ironically, in the book, the 3D diagram -- which is harder to draw --
is drawn much more accurately.
\sidexfig
{equipot-inverse-r}{}
{Equipotentials $V=1$, $V=2$, and $V=3$ for the $1/r$ Potential}{}
{equipot-inverse-r-5}{}
{Equipotentials $V=1$ through $V=5$ for the $1/r$ Potential}{}
It would be even better to show more contours, as in \jfigure
{equipot-inverse-r-5}.
\xitem{induction-not} On page 827 in example 28.10, it shows a proton
(not a test charge) initially at zero distance from the surface of a
charged sphere. We have to assume the sphere is made of conducting
material, because the exercise speaks of ``the'' potential of the
sphere, and it would be impossible for a non-conducting sphere to
remain an equipotential under the conditions of the experiment.
The text says \ That's quite
wrong. That's the worst sort of equation-hunting, \ie. applying an
equation in a situation where it is not valid. It leads to getting
an answer that is wrong by a factor of infinity.
There is a theorem about a spherically-symmetrical static
distribution of charge, but that's not what we have here, because of
the image charge induced by the proton. At zero distance, the
induced-dipole interaction is infinitely stronger than the
first-order Coulomb interaction. The text ignores this
infinitely-large contribution.
\xitem{kirchhoff-energy} On page 847: Kirchhoff's law is not
equivalent to conservation of energy. Energy is always conserved,
but Kirchhoff's law is not always valid.
\xitem{bulbs-in-series} On page 917, exercise 36 calls for wiring two
incandescent bulbs in series. It asks \
There is no chance that students will be able to answer this question
correctly. Incandescents are infamously non-Ohmic.
\xitem{relativity} On page 1064, Galileo's principle of relativity is
discussed for the first time. I suppose it is better late than
never, but this seems remarkable to wait so long to discuss a
principle that has been at the heart of physics since Day One of
modern science (1638).
What's worse, on page 1009, it says the calculations \ because they \. Let's be
clear: There is nothing wrong with Galileo's principle of relativity,
as he stated it in 1638. Indeed the calculations on pages 1008-1009
are not quite right ... but that's for reasons having nothing to do
with Galileo.
\xitem{misch} On page 1075, the book introduces the modern (post-1908)
idea of proper time, but greatly undervalues it. It is used only as
a stepping stone to calculate pre-1908 quantities such as the dilated
time.
\xitem{masch} On page 1088, equation 36.32 is a
formula for the four-dimensional velocity.
\jeal{4-velocity}{
p &=& {\Delta{x}\over\Delta\tau}
}
We remark in passing that it would make a lot more sense to use an
actual derivative, rather than a ratio of finite deltas.
However, the main point is that the book doesn't do anything useful
with this formula. Instead, it immediately converts it to an
expression involving the 3-velocity and a factor of gamma, namely
equation 36.33. The rest of the discussion emphasizes the latter.
\end{description}
\section{References}
\label{sec-ref}
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\bib{one-kind-of-charge} John Denker,\\
``One Kind of Charge''\\
\ahrefbib{}
\bib{subatomic} Steven Weinberg,\\
\book{The Discovery of Subatomic Particles} Revised Edition
%% Ben Franklin, page 13.
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\end{document}
\section{References}
\label{sec-ref}
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\bib{m-i-errata} ``Errata for \book{Matter and Interactions} 3rd edition\\
\ahrefurl{http://matterandinteractions.org/Content/Errata/Errata_3e.pdf}
\bib{reactball} Rawlings ``REACTBALL''\\
\ahrefurl{http://rawlings.com/product/reactball/REACTBALL(Rawlings)}
\bib{causation} John Denker,\\
``Cause and Effect''\\
\ahrefbib{}
\bib{spacetime-welcome} John Denker,\\
``Welcome to Spacetime''\\
\ahrefbib{}
\bib{weight} John Denker,\\
``Definition of Weight, Gravitational Force, Gravity, $g$,
Latitude, et cetera''\\
\ahrefbib{}
\bib{symplectic-integrator} John Denker,\\
``Basic Properties of a Symplectic Integrator''\\
\ahrefbib{}
\bib{earth-shape} Benny Lautrup,\\
``Hydrostatic shapes''\\
\ahrefurl
{http://www.cns.gatech.edu/~predrag/courses/PHYS-4421-10/Lautrup/shapes.pdf}
\bib{rotating-frame} John Denker,\\
``Motion in a Rotating Frame''\\
\ahrefbib{}
\bib{thermo} John Denker, \\
``Modern Thermodynamics''\\
\ahrefurl{./thermo/}
\bib{wavefunctions} John Denker,\\
``Models and Pictures of Atomic Wavefunctions\\
\ahrefbib{}
\bib{coherent-states} John Denker,\\
`Coherent States''\\
\ahrefbib{}
\bib{def-entropy} John Denker,\\
``Quantifying Entropy'' in chapter 2 of \book{Modern Thermodynamics}\\
\ahrefurl
{http://www.av8n.com/physics/thermo/entropy.html#sec-quantify-s}
\bib{pressure-everywhere} John Denker,\\
``A Fluid Has Pressure Everywhere''\\
\ahrefbib{}
\bib{power-plant-efficiency} John Denker,\\
``Power Plant Efficiency'''\\
\ahrefbib{}
\bib{white} John Denker,\\
``Why White Things are White''\\
\ahrefbib{}
\bib{contact-electrification} John Denker,\\
``Contact Electrification''\\
\ahrefbib{}
\bib{one-kind-of-charge} John Denker,\\
``One Kind of Charge''\\
\ahrefbib{}
\bib{battery} John Denker,\\
``How a Battery Works''\\
\ahrefbib{}
\bib{magnet-relativity} John Denker,\\
``The Microscopic Origins of the Magnetic Field''\\
\ahrefbib{}
\bib{rule-law} John Denker,\\
A discussion of rules, laws, theorems, et cetera, in ``Scientific Methods''\\
\ahrefurl{http://www.av8n.com/physics/scientific-methods.htm#main-rule-law}
\bib{blue-sky} John Denker,\\
``Why the Sky is Blue''\\
atom-intro.tex-\ahrefbib{}
\bib{kepler-equal-areas} John Denker,\\
``Kepler's Equal-Area Law, Angular Momentum, and the Laplace-Runge-Lenz Vector''\\
\ahrefbib{}
\bib{ajp-e-m} Ruth Chabay and Bruce Sherwood,\\
``Restructuring the introductory electricity and magnetism course''\\
AJP \vol{74}, 329-336 (2006)\\
\ahrefurl{http://ajp.aapt.org/resource/1/ajpias/v74/i4/p329_s1}\\
\ahrefurl{http://matterandinteractions.org/Content/Articles/AJP-EandM.pdf}
\bib{decorated-symbols} John Denker,\\
``Decorated Symbols (\eg. x-bar, q-dot, v-vector) in HTML''\\
\ahrefbib{}
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}