What's wrong with this textbook?

A homework question

It started with a homework question
Chapter 1 assessment (p. 40)

If the statement is true, write true. If it is false, change the underlined word or words to make the statement true.

10. The distance an object travels in one unit of time is called acceleration.

As written, the statement is false, but you can't make it true by changing the word acceleration. We don't have a word for distance traveled in one unit of time.

My son was frustrated by this, so I started reading the text to figure out what was going on. I soon found the glossary, and the entry for speed

Speed The distance an object travels in one unit of time. (p. 20)
This, of course, is flat wrong. The distance an object travels in one unit of time is a distance, not a speed. The glossary entry referred back to page 20 of the text, where I found a discussion of speed, and the statement
the speed of an object is the distance the object travels per unit of time.
This is a passable definition of speed, although it is not marked as such in the text. It is technically correct: the little word per makes all the difference. Still, it's not a very good definition. The "unit of time" is irrelevant, and obscures the symmetry between time and distance in the definition.

OK, so the book has a typo. These things happen, right?

Wrong. It's not a typo. The people who wrote this book didn't know what they were talking about, and it shows. The book is shot through with mistakes like this.

In this particular case, it appears that

If you understand the physics, this sort of thing is annoying. If you don't—for example, if you are a student trying to learn physics—it is maddening.

Motion, Forces and Energy

The book is Science Explorer: Motion, Forces and Energy, published by Prentice Hall. Motion, Forces and Energy is a big hardcover textbook. The cover photo shows a ferris wheel, with lots of color and motion. It has 224 pages, divided into There is no author listed on the cover, so I turned to the front matter to see who wrote it. It turns out no one wrote it...or rather...it wasn't written...that is...

Science Explorer isn't a book: it's a program: a collection of 15 textbooks treating different areas of science

The whole thing was put together by Prentice Hall, with a cast of thousands—dozens, anyway. The books credits Despite the appearance of 1 "book author", I'd be hard pressed to say that anyone actually wrote this thing. Motion, Forces and Energy was created—fabricated—by a corporation. Still, there were people involved in its fabrication, and part of the problem may be that they were the wrong people. There are no physicists among the 13 Tufts University Program Reviewers, and only one among the 27 Content Reviewers. Eight of the Program Reviewers are in engineering departments, which is a bit odd, considering that Science Explorer is a science curriculum, with a heavy emphasis on earth and life sciences.

The front matter makes much of the Tufts University Program Reviewers; maybe Prentice Hall got a volume discount on Program Reviewers from Tufts. The Program Reviewers don't seem to have done much for the quality of Motion, Forces and Energy. It would be interesting to know what they told Prentice Hall about the book.

Whatever the facts, I hope Tufts was well paid, because the results reflect poorly on them.

Is this book really necessary?

Before delving further into the failings of Motion, Forces and Energy, let's step back and consider whether this book should exist at all. I think that it shouldn't.

The Science Explorer program is targeted at the junior high school market. Junior high schools generally encompass ages 11 to 14. I don't know whether Prentice Hall markets Science Explorer for a particular grade level. Our schools use it in the 6th grade, where the students are 11 and 12 years old.

I don't think that 12-year olds should be studying science; at least, not from books. I think 12-year olds should be outside, skipping stones and catching frogs. Science is the study of nature, and it must be grounded in the experience of nature. There will be time for books later.

If 12-year olds are going to study science in books, they should study a concrete field, and focus on the descriptive aspects of it. Some of the other titles in the Science Explorer program, such as Animals and Astronomy, can be made accessible to 12-year olds. Motion, Forces and Energy cannot.

Motion, forces, and energy are all elements of physics. Physics is highly abstract, and 12-year olds are not. Abstract thought doesn't develop in humans until around age 14. Without abstraction—in particular, without mathematics—you can do almost no meaningful physics. Without mathematics, physics degenerates into tedious vocabulary, pointless classification, and gee-whiz experiments.

A book titled Motion, Forces and Energy simply can't be written at the junior high level. I haven't seen them, but I suspect that other titles in Science Explorer that treat physical sciences, such as Electricity and Magnetism and Sound and Light, suffer from the same problem.

Less than meets the eye

Motion, Forces and Energy seems substantial when you pick it up. It is big (8.75" x 11.25"), hardcover, over 200 pages. It has some heft. When you thumb through it, you see text, pictures, equations, experiments.

The book seems less substantial as you read it. The pages have generous margins. There are lots of pictures and sidebars. The text is set in a big typeface. There are chapter summaries and review questions and homework questions. There are whole sections dedicated to tangential material. After all that, there isn't much room for exposition. Important concepts, such as speed and force, are covered in just a few paragraphs.

Arguably, 2 or 3 paragraphs is all that a 12-year old can absorb on a given topic, especially in an abstract field like physics. But that just gets back to the point that 12-year olds shouldn't be studying physics in the first place.

Alternately, we could see this as yet another example of dumbing down (the ongoing trend to limit and simplify the contents of textbooks). Despite the pejorative term, there isn't necessarily anything wrong with this. A school that wants to teach a limited and simplified curriculum would naturally choose a text that has a limited and simplified presentation. The problem with Motion, Forces and Energy is that even within its limits, so much of what it teaches is wrong.

The Nature of Energy

One place where Motion, Forces and Energy fails badly is the discussion of energy. Energy is one of the most complex and subtle concepts in elementary physics. It would be understandable if a book at this level simply omitted any discussion of energy. However, the word "energy" appears in the title, and the book devotes an entire chapter to the subject. Chapter 5 is titled Energy and Power, and comprises 4 sections
  1. The Nature of Energy
  2. Energy Conversion and Conservation
  3. Energy Conversions and Fossil Fuels
  4. Power


The first section undertakes to define and classify energy. In a passage headed What is Energy?, it offers this definition
the ability to do work or cause change is called energy
This is nonsense, like Jabberwocky
'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogoves,
And the mome raths outgrabe.
The problems isn't that the definition is wrong, the problem is that the words simply don't mean anything; at least, nothing useful to a physicist. Energy is a physical quantity: you can measure it, and get a value expressed in numbers and units. The definition given above doesn't tell you how to measure energy, or even suggest that energy can be measured.

Mechanical energy

The text goes on to classify energy according to its various forms, beginning
There are two general kinds of energy. The two kinds of energy are kinetic energy and potential energy. Whether energy is kinetic or potential depends on whether the object is moving or not.
On its face, this passage says that all energy is either kinetic or potential, which is false. Still, it could serve in an elementary text, provided that the text restricted itself to those two forms. However, Motion, Forces and Energy goes on to discuss other forms of energy, such as and the text becomes more and more tangled as it attempts to fit all these into a botched classification scheme. For example, the true definition of mechanical energy is simply
mechanical energy = kinetic energy + potential energy
But you can't say that unless you've correctly defined potential energy as work done against a conservative force, and you can't do that unless you've explained what a conservative force is, and you can't do that in the few paragraphs that the book allots to this topic. Instead, we find this tortured prose
Mechanical energy is the energy associated with the motion or position of an object. Mechanical energy can occur as kinetic energy or potential energy.
"associated with"? "can occur"? What does that mean? What is it supposed to mean? What can a student possibly make of it?

Chemical energy

The paragraph on chemical energy says
Chemical energy is potential energy stored in chemical bonds that hold chemical compounds together.
There are several problems here. First, chemical energy is not potential energy. Second, this statement misapprehends the nature of chemical energy. Energy isn't "stored" in chemical bonds. When a bond forms, energy is released—made available—for other uses. If you have the bond, the energy is somewhere else. Saying that energy is stored in chemical bonds is wrong; it's like saying that energy is stored in smoke and ash.


A section headed The Meaning of Work says
In science you do work on an object when you exert a force that causes the object to move some distance
and culminates in the formula
Work = Force x Distance
However, if we look in the glossary, we find this entry
work Force exerted on an object that causes it to move.
This is wrong, in much the same way that the glossary entry for speed is wrong: it asserts that work is a force, rather than a product of force by distance. The fact that the glossary writer repeatedly failed to learn basic physical concepts from this text speaks to its utter inadequacy.

A sack full of energy

The discussion of energy is wrong in many particulars. However, the text is also flawed in a broader sense: the implicit concept of energy that it presents is misguided. It talks about energy as if it's stuff that you can carry around in a sack. It talks about different forms of energy as if they were animals in a bestiary, to be named, described, and classified:
Energy is all around you in many different forms.
The school bus you ride in, a frog leaping through the air, and even the sound you hear all have mechanical energy.
When you receive a shock from a metal doorknob, you experience electrical energy. Moving electric charges produce electricity, and the energy they carry is called electrical energy.

Energy isn't like that. Energy is like...is like...energy is like money. Really, it is. Money has many different forms, such as

Some of these can, indeed, be carried around in a sack, but most people understand that money is fundamentally an abstraction: an abstraction that inheres not in the tokens that represent it, but in the relationships among people that establish its value. Money is neither created nor destroyed: it just moves around from pocket to pocket and account to account. There are rules for keeping track of money as it moves around; people who know all the rules are called accountants.

Like money, energy is an abstraction, inherent not in any particular thing or substance, but in the states of physical systems. Energy is neither created nor destroyed: it just moves around and changes form. There are complex rules for keeping track of energy as it moves and changes; people who know all the rules are called physicists. Different forms of energy aren't so much different kinds of stuff as they are different rules for accounting for it.

Define the universe. Give three examples.

Humans are rather good at abstracting from examples; that's why we use them to teach and communicate. However, examples only work if there is something to abstract: if the things cited share something that distinguishes them from other things, not cited.

The text says "Energy is all around you", and gives examples like

[A] leaping frog is an example of mechanical energy, and [...] melting ice is an example of thermal energy.
Chemical compounds, such as chocolate, wood, and wax, store chemical energy. [...] Chemical energy is stored in the foods that you eat and in a match that is used to light a candle. Chemical energy is even stored in the cells of your body.
The bewildering diversity of things cited as examples of energy is presumably intended to convey the idea that everything has energy. The problem with this is that if everything has energy, then listing examples of things that have energy doesn't convey a distinction. There aren't any other things that don't have energy from which they can be distinguished.

There is something both useless and patronizing about examples like these.

The true, the false, and the empty

Much of what the text has to say about energy isn't so much false, as it is empty. For example, the book displays this false-color image of a human head CT scan of a human
      head, with the caption
Electromagnetic energy is used to take a CT scan
This is true, but it doesn't tell you anything about energy, or electromagnetic energy, or CT scans, or how one is used to make the other. You could just as well put the picture of the CT scan in an accounting text, with the caption
Money is used to pay for a CT scan
Again, a true statement, but one that doesn't tell you anything about deductibles, or co-pays, or Medicare reimbursement schedules, or supply and demand, or amortization, or labor costs, or return on investment. It's empty.

An experiment with speed

For all its problems, it looks like Prentice Hall tried to do a good job with Motion, Forces and Energy. For example, the book is full of sidebars suggesting Evidently, someone told them that science doesn't come just from a book: that you have to go out and touch nature, try things, experiment. It's all very impressive on a casual reading, but much of it doesn't stand up to scrutiny. For example, here's a sidebar from page 31, headed "Science at Home"
Have each member of your family measure the length of the white part at the end of one fingernail. Write down the results (and which finger you used) and mark your calendar for a date in exactly three weeks. On that day, measure the new length of the white part of the same fingernail. Then calculate the speed, in millimeters per day, at which your fingernail grew. Discuss with your family how your results compare with the typical speed with which continents move.
Although it sounds reasonable, this experiment won't work. The procedure described doesn't measure growth, it measures growth net of wear and trimming. Even assuming that the student will refrain from trimming that nail for three weeks, the results are going to be strongly biased towards zero.

A better procedure would be to mark the nail, and measure the distance from the cuticle to the mark. A typical 6th grade classroom probably has some girls wearing fingernail polish, so you could even conduct this as a natural experiment. But then

and so fingernail polish gets edited out and the book goes to press with an experiment that doesn't work.

Textbook Politics

The problems discussed above aren't unique to Motion, Forces and Energy, and they aren't new. Richard Feynman saw similar problems when he reviewed mathematics textbooks for the state of California 40 years ago
The [...] books were so lousy. They were false. They were hurried. They would try to be rigorous, but they would use examples (like automobiles in the street for "sets") which were almost OK, but in which there were always some subtleties. The definitions weren't accurate. Everything was a little bit ambiguous—they weren't smart enough to understand what was meant by "rigor". They were faking it. They were teaching something they didn't understand, and which was, in fact, useless, at that time, for the child.
— Richard P. Feynman
Something is wrong—obviously, seriously, and persistently wrong—but what? And more importantly, what do we do about it? I don't think the fault lies with any of the actors. I think the underlying problem is that the government is running the schools, and it shouldn't be. Because the government runs the schools, the process for choosing textbooks is ultimately political, not scientific or educational. And politics is a bad way to choose textbooks.

If we privatized the schools, then parents would have a choice of where to send their children, and schools would compete for students. Schools would compete based on the quality of their facilities, their teachers, and, yes, their textbooks. If a parent were unsatisfied with a school—for whatever reason—they could send their child to a different one, rather than just complaining about it on the web.

Our tertiary schools (colleges and universities) are largely private, and are the best in the world. I don't see why we couldn't do the same thing with our primary and secondary schools.


flat wrong
Never mind that if it were true, it would be the answer to the question.
cover photo
Not that the students will see much of it. Schools require students to hide their textbooks under book covers.
big typeface
doubtless touted as "easy to read" by the sales people
It is like Jabberwocky in that the words lack referents. In another sense, it is very unlike Jabberwocky: Jabberwocky is strong, clear, definite writing; this is not.
the glossary writer
presumably, an adult
money is neither created nor destroyed
patently false: humans create and destroy money. However, individuals normally behave as if this were true.
energy is neither created nor destroyed
not strictly true, but the exceptions needn't concern us
chocolate, wood
these are not chemical compounds MRI scan of a human head
It's empty
It is also—very likely—a fudge. The profile of the nose identifies the CT scan as a cross section in the mid-sagittal plane; however, the eyeball does not exist in that plane. Compare the CT scan with this MRI scan, also in the mid-sagittal plane. Figuring out why the editors felt compelled to draw an eye on a CT scan is left as an exercise for the reader.
measure the distance from the cuticle to the mark
This presumes an understanding that nails grow from the root, unlike—say—trees, which grow from the tip.
A.K.A. fingernail polish remover
school committees are elected
or appointed by elected officials

Further reading


"This isn't right. This isn't even wrong."
— Wolfgang Pauli
I wrote it. That is to say, I collaborated in writing it. No book is produced individually, as you know.
— George Orwell, 1984

Steven W. McDougall / resume / swmcd@world.std.com / 2004 Jan 01