Review
by Barry Feierman and the reviewers of the Second Report.

Physics: A First Course by Tom Hsu and published by CPO Science

Readability: The book is excellent for the intended audience of 9th graders. The chapters are reasonably short, have large enough print, single column with excellent support materials in the form of illustrations and pictures.

The sections on each chapter called Connections are used to show the applications of the concepts to practical life or to show the history of discovery of the physical laws discussed.

The end-of-chapter questions are excellent. There are sections that examine a mastery of the vocabulary (low level), sections that examine knowledge of the concepts, questions that ask about applications, and finally problem solving with some reasonably difficult questions. Chapters end with suggestions for further research called “Applying Your Knowledge”. I would, however, like to see a few extra hard “challenge questions” which involve a bit more analytical thinking for the brightest 9th graders.

Suitability for a Physics First course: I think the book is well designed for the intended audience of 9th graders who are just learning about working with equations and graphs. The variables in each equation are carefully defined, units are completely metric, and the sample problems are excellent. The layout is particularly well done and uncluttered.
However, the book must be held so that the pages are wider than they are tall, making it somewhat difficult to keep the book balanced while reading. It’s also a pretty hefty weight to carry around all year.

Contents of Book: The text covers all of the major topics typically found in a high school physics course in a traditional order, more or less. After an opening chapter discussing what physics is and the role of measurement, the text discusses matter and energy, systems of variables, scales, models, and how to measure distance and time, unit conversions, and finally introduces the concept of speed in terms of the ratio of distance to time as well as the slope of a distance-time graph.

The author does a good job of explaining graphs; how they are made, how the axes are defined, independent and dependent variables, and finally does an excellent job showing how to calculate the slope of a line and what that slope means.

Unit One (three chapters) in mechanics develops Newton’s Laws of Motion, the concepts of velocity and acceleration, gravity and free fall, and finally the Third Law of Motion and the Law of Conservation of Momentum. I would like to see in chapter one a discussion of the history of the origin of the kilogram and the meter to give readers a sense of how difficult it was in 1800 to come up with universal standards for mass, length, and time, as well as how and why the standards have changed.

Unit Two covers Energy and Systems defining work, power, simple machines, forces, vectors (without any mention of trigonometry), friction, torque and equilibrium. Unit Two ends with a nice chapter on circular motion, centripetal force, satellites, and center of mass.

Unit Three gets the reader into temperature, heat, specific heat, heat transfer, properties of matter, behavior of gases, and structure of the atom. The depth is suitable for a 9th grade level.

Unit Four is all about energy and change, energy flow, power, changes in matter, chemical bonds and chemical reactions, and nuclear reactions. It is sufficient in depth to give a good understanding of atoms for a student to enter a full-year chemistry or biology class following physics. Unit four ends with a chapter on relativity, both the special and general theory.

Unit Five is the traditional chapter on electricity, except the author begins with current and electric circuits, defining current, voltage and resistance and developing Ohm’s Law. The next chapter covers series and parallel circuits and electric power. The last chapter in the electricity unit covers static electricity and Coulomb’s Laws, conductors and insulators, and how capacitors work. Thus the topics are introduced in the reverse order from most introductory books. By doing the topics in this order, the history of electricity is lost until you get to the last chapter.

Unit Six is the traditional electricity and magnetism connection, where the text develops the idea of magnetic forces, magnetic fields, the Earth as a magnet, and how generators and motors work. The last chapter in this unit introduces the idea of fields (electric and gravitational).

Unit Seven is a very traditional waves chapter where the author introduces the idea of harmonic motion and its graphs, again without any mention of trigonometry. The next chapter covers waves in general, frequency, wavelength, wave speed, and how waves move through a medium. The last chapter is a nice development of sound and music.

Unit Eight is a very nice section of three chapters covering the nature of light, color, optics, and the physical nature of light leading to the idea of photons and the electromagnetic spectrum.

Accuracy: I would give the CPO Science book a very high rating if it were not for the myriad of mistakes, both conceptual and numerical that are scattered throughout the entire textbook. For any book that has been reviewed by a number of teachers, I am surprised that there are so many errors.

Errors found and discussed.

p. 18 the author introduces very nicely the notion of “per” meaning for each or for every, but uses the very unconventional abbreviation of “sec” for seconds. Thus, m/sec becomes the standard way speed and velocity are defined, unlike just about every book written on physics which uses “m/s” for the abbreviation of meters per second.

p. 19 the author discusses in a side panel the reason that the symbol “v” is used to represent speed and then discusses velocity as requiring both speed and direction. However, the author fails to make any mention of the difference between distance and displacement, thus confusing later definitions of acceleration.

p. 28 the author keeps mentioning that “force creates changes in motion” while it would be much better the first time to consistently use the notion that “net” forces create changes in motion. It is a simple matter to introduce the idea of a net force if there are two or more forces acting on an object. This does not need the development of trigonometry.

p. 29 do we really want to say that “objects want to keep doing what they are already doing” in the process of introducing the word inertia? There is no reason to introduce needs and wants when talking about nonliving matter.

p. 29 “some objects resist changes in motion better than others” I think you can introduce more resistance or less resistance but don’t need to complicate this concept with the idea of a “better” resistance.

p. 30 the idea of a force is introduced before the concept of acceleration, thus the newton is that force which when acting on one kilogram will cause the kilogram to “speed up by one meter per second per second”. First, I’d like to see acceleration introduced so that one topic can feed into the next one, and I’d like to reinforce that a newton can speed up or slow down a moving object. You might get away with the definition if you at least say that the newton of force causes a change in the velocity. The author does not mention here that forces can produce changes in either speed, direction, or both. It could all be clearer by just mentioning that acceleration causes changes in velocity and avoid the use of the word speed.

p. 32 again, the author says that “acceleration is the rate at which your speed increases.” I think this is just bad at this point of an introductory book. Acceleration can also decrease your speed.

p. 33 the author uses the very unconventional notation of m/sec for the more typical m/s short-hand description of meters per second. The author does a good job in introducing the concept of meter per second-squared as meters per second per second or (m/s)/s.

p. 33 caption “the only way a moving object can have an acceleration of zero is to be moving at constant speed in a straight line.” That is a good example, except for when the object is at rest and has an acceleration of zero. At this point in the book, before covering vectors, the drawing is very confusing.

p. 34 the discussion of positive and negative acceleration is just wrong. A positive acceleration “is when an object speeds up” the author says. What about a car in reverse and the driver steps on the brakes? Isn’t that also a negative acceleration, except the car is slowing down? Then the author says “a negative acceleration is when the object slows down. What about a car in reverse and the driver steps on the gas pedal? Why not just say that the sign of the acceleration is the same sign as the change in velocity and talk about positive and negative as just two opposite directions?

p. 35 “the acceleration of an object is directly proportional to the net applied force”. This is fine, but the author has not (yet) defined what direct proportion means. It would only take another few lines of text to say something like “doubling the force doubles the acceleration, triple the force and you get triple the acceleration.”

p. 35 “force is not necessary to keep an object moving at constant speed”. Better to say “in the absence of any friction …”, but every kid knows you have to keep pedaling your bike on a horizontal surface to keep moving at a constant speed.

In the next few examples I think that in order to make it simple and easy to understand, the author makes it much harder to get a truer picture of the concept of acceleration in terms of change:

Section 2.4 p. 46 “the slope of a position-time graph is the speed” It would be far better to use the word velocity instead of speed because of the complications which arrive when you talk about acceleration later on.

p. 47 again “slope equals speed”. The slope can be zero, positive, or negative, yet speed is a scalar quantity, so just call the slope of a position-time graph the velocity.

p. 49 Fig 2.19 is nice but you could also show what happens with a negative velocity graph and not restrict yourself to just “positive speeds” in the illustration.

p. 49 “constant acceleration means that an object’s speed changes by the same amount each second”. It would be far better to use the word velocity.

p. 61 “momentum is always calculated with velocity instead of speed because the direction of momentum is always important. Yes, so if you can say velocity here you can say it in the section dealing with acceleration as a rate of change of velocity with respect to time.

p. 62 the equation for impulse is given but with no insight as to where it came from. It would be easy to define impulse by equating what students already know:

a = F/m and a = change in Velocity/time

Thus FΔ t = mΔV.

p. 64 caption at bottom of page about the Calorie. The author defines the Calorie (capital C) as 4187 joules without any mention of the calorie as the energy to change the temperature of one gram of water by one degree Celsius.

p. 68 the author introduces the kinetic energy formula without any notion of where it comes from. It is easy (even as a footnote) to show that if work equals force times distance that F d = ma d and a = (Vf – Vo) / t and d = average velocity x time = (V0 + Vf) / t so even a student in algebra one can see how you get the ½ m (Vf2 - Vo2) formula.

p. 75 the rubber ball has an elastic collision and bounces back up with the same speed it had when it hit the floor” as long as the collision with the floor is elastic.

p. 76 example problem question asks “what force” did the floor exert on the ball?
Better to say “what average force” did the floor exert because the force was not constant.

p. 76 here is the derivation for impulse that is well done. The same could be done for work in terms of KE.

p. 78 caption might explain why there are two fuel tanks.

p. 82 problem #11 “how much energy is needed to move a 10,000N car 20 meters”?
You can’t tell. Are you pushing with a horizontal force of 10,000 N? Which way is the car moving?

p. 83 problem #5 “The energy is food” should read “in food”

p. 87 is it possible to introduce the idea of “negative work” such as the work done by the brakes on a moving car?

p. 98 Fig 4.12 look at the drawing for B. Do you see the problem? One rope goes nowhere - artistic license?

p. 119 – 121 you might consider introducing the equation: f = µN since you’ve got all the pieces there.

p. 137 Fig 6.5 look carefully at the drawing and note that the horizontal velocity vector Vx is changing yet the text says it is constant

p. 140 why is the 45 degree angle the longest range? I think you can explain this more clearly without the use of trig.

p. 149 is it possible to show where the centripetal force is derived?
The author just states that the centripetal force is directly proportional to the square of the object’s linear speed with no mention of how we know this.

p. 154 “at a launch speed of 8 km/second the curve of a projectile’s path matches the curvature of the Earth”. I think you want to say that at an orbital speed of 8 km/s - no projectile is launched at a speed of 8 km/s.

p. 154 Fig 6.23 the directions of the arrows for velocity should be at right angles to the radius of the Earth. And again, it’s not the “launch velocity” that has to be high, but the orbital (final) velocity. The Space Shuttle certainly does not launch at 8 km/s.

p. 159 confusing drawing of “lift” on a helicopter as helicopter blades tilt. Isn’t lift always perpendicular to the vertical?

p. 166 “the impact of the marble is much to small ….” - You mean much too small.

p. 167 Fig 7.3 why is the hydrogen about 3 times the volume of the oxygen?

p. 174 the graph illustrates temp vs. time. It would be nice to follow up with a graph of temp vs. energy and talk about the energy needed to change the state of matter.

p. 176 heat flows from a warmer object (higher energy) to the cooler one (lower energy). I think you mean from the warmer object (greater temperature) to the cooler object (lower temperature). Which has more energy: a cup of tea or a large iceberg? The iceberg. But heat doesn’t flow from the iceberg to the cup of tea. Heat doesn’t flow from high energy to low energy… but from high temperature to low temperature.

p. 177 “the calorie is the quantity of heat needed to increase the temperature of one gram of water by one degree Celsius”, but in the caption below, it shows one Calorie (kilocalorie) changing the temperature of one gram of water from 10 deg C to 11 deg C.

p. 178 “knowing the specific heat tells you how quickly the temperature of a material will change”. That has something to do with conductivity. I think you could change quickly to how easily or how difficult.

p. 178 specific heat can be defined as the energy needed to raise or lower the temperature of one kilogram by one degree C.

p. 180 check the calculations here. 4 joules will not change the temperature of one kg of silver by 17 degrees C. I think you mean 0.017 degrees. Or 4 kJ of energy.

p. 184 there is a graph with exponential scales on both X and Y axes, and no label on the X axis, which is very confusing for a 9th grader. Why not just say that the energy emitted by a black body goes up with the fourth power of the absolute temperature? The graph doesn’t convey any useful information to a 9th grader.

p. 203 Fig 8.20 what is the liquid? It doesn’t mention.

p. 211 “the relative humidity tells how much water vapor is in the air compared to how much the air can hold”. What does this convey? How does the air “hold” water vapor? That’s a bad concept to see in print. There are better ways of explaining relative humidity in terms of the saturation point where the vapor condenses.

p. 219 Fig 9.2 it would be good to attach a date to the Thomson model of the atom

p. 291 mention WHO coined the phrase “big bang” theory.

p. 298 “electricity usually means the flow of electric current”. Isn’t this redundant? Why not say the “flow of electric charge” or the “current in a circuit”. Current already indicates something is flowing.

p. 302 “Differences in voltage are what causes electric currents to flow”. Same error in language. Differences in voltage cause charges to move.

p. 309 “electrical resistances of many materials, including those in light bulbs, increases as temperature increases. Yes, you might also in one sentence mention that resistance in semiconductors (like carbon) decreases with temperature.

p. 309 Fig 13.13 I think you want the caption to read 100 watt bulb since a 100 watt bulb can’t draw a power of 145 watts.

p. 324 “if a circuit draws too much current the battery voltage will drop and fewer charges will flow”. You might mention this is because the battery also has some internal resistance, and some current just heats up the battery converting chemical energy to thermal energy.

p. 347 “some valence electrons ….”, best to mention what a valence electron is.

p. 505 bottom of page, the image should be inverted.

p. 507 Fig 23.13 that telescope won’t magnify if you follow the light rays. The objective lens needs to have a longer focal length than the eyepiece.

p. 522 “if you shake a magnet up and down 100 million times per second you would make an FM wave” NO NO. You just make a carrier wave at a frequency of 100 MHz, or the same frequency of the typical FM radio band. But to make an FM signal, you need to modulate it.

p. 526 radio towers do not need to be one-quarter of a wavelength high.
Most TV towers just have the radiating element on the top of the tower.
And some vertical antennas are 5/8 wavelength to maximize the low-angle radiation.

p. 534 “phosphorus atoms glow in the dark” … can you say why the light energy is delayed in photoluminescence?