Reviewing a middle-school book in the Prentice Hall Science series

What a Display of Ignorance!

Lawrence S. Lerner

• Page 12: A photograph shows two fighter jets and a propeller-driven tanker plane, and the caption says: "These Navy fighter jets are traveling at tremendous speeds relative to an observer on the ground. But because they are moving at the same speed, they are not moving relative to one another. This enables them to hook up and refuel in midair." The jets' speed with respect to each other is irrelevant. All that matters is each jet's speed with respect to the tanker.

• Page 26: "The stopping distance of a car is directly related to its momentum." The stopping distance depends not on momentum (which is proportional to velocity) but on kinetic energy (which is proportional to the square of velocity).

• On page 27: "Momentum is always conserved." No, momentum is conserved in an isolated system only.

• Page 40: "Automobiles are able to stop because the action of the brakes increases friction between the tires and the road." Not true. (Have you ever applied your brakes while driving on icy pavement?) On the same page, a picture shows bicycle racers going around a curve on an indoor track, and the caption says: "Cyclists rely on friction to hold their bicycles on the ground." Precisely wrong. The curve is steeply banked so that the cyclists will not have to rely on friction.

• Page 71: "[A floating iceberg's] weight must be less than or equal to the weight of the salt water that it displaces." By jumbling two different ideas, the writers have produced needless confusion. If a piece of ice is floating, then its weight is equal to (not "less than") the weight of the water that is being displaced. But the weight of the ice is less than (not "equal to") the weight of the water that would be displaced if the ice were entirely submerged.

• Page 73: "According to the modern theory of plate tectonics and continental drift, the continents can be thought of as floating in a sea of slightly soft rock . . . . The height of any continent . . . depends in part on the difference between its density and the density of the rock on which it is floating." Plate tectonics and continental drift have nothing to do with this. What applies here is the classic principle of isostasy.

• Page 79: "Pressure is a force that acts over a certain area." No, pressure is not a force, and knowing the difference between pressure and force is vital in understanding the behavior of fluids.

• Page 79: "Buoyancy is the phenomenon caused by the upward force of fluid pressure." But the same page also says that "All fluids exert pressure equally in all directions" and "Pressure applied to a fluid is transmitted equally in all directions." Then how could pressure cause buoyancy, if buoyancy is a "force" that is directed only "upward"?

• Page 81: The writers tell the densities of gold, pyrite and mercury, and then they ask the student to design an experiment for distinguishing gold from pyrite. They apparently want an answer that involves putting the gold into mercury, putting the pyrite into mercury, and seeing which one floats and which one sinks. That is a dumb idea, because gold dissolves in mercury.

• Page 90: "[W]hen you use a shovel to move a rock, your effort is opposed by the rock's weight." No, your effort is opposed by the shovel. What the rock's weight opposes is the force that the shovel exerts on the rock.

• Starting on page 90, the text repeatedly says that work is conserved. That is false and is contradicted by the text itself, which points out that all real machines yield less work than is put into them. The writers don't grasp the difference between work and energy.

Nor do the writers have much sense of real-world quantities. On page 17, they guess that a cheetah can run at 2 kilometers a minute for 4 minutes! (Cheetahs may attain such a speed, but only for a matter of seconds.) On page 19 they ask the student to imagine that he is rowing a boat at 16 kilometers an hour! On page 33 there is an exercise involving freight cars that travel directly toward each other, one moving at 14 meters a second, the other at 10 meters a second, until they collide. The writers ask: "If the two cars collide and stick together, what will be the direction of their resulting motion?" Answer: If two freight cars collide when their relative speed is 24 meters a second, or about 50 miles an hour, they will end up as scattered debris.

• Page 35: We are told that Newton went to Woolsthorpe because there was a plague epidemic "throughout London." (London? Newton went to Woolsthorpe from Cambridge, after the epidemic led to the closing of Cambridge University.) Worse, the writers actually believe the story about Newton and the apple -- and they misconstrue it as well!

• Page 41: "Isaac Newton . . . recognized that if friction was not present, an object in motion would continue to move forever. No, that was Galileo.

• Page 44: In the teacher's edition, a note tells the teacher this: "Within our own solar system, astronomers have noticed a disturbance in the orbits of Uranus and Neptune, leading them to believe that perhaps a tenth planet with a large gravitational field may be located beyond Pluto." The phrase "a large gravitational field" is moronic, and the whole story is false. It seems to be the last gasp of the tale of Planet X, a story that was popular in tabloids of the 1930s. Few astronomers took it seriously, even in those days, and no astronomer takes it seriously today.

• Page 47: "Legend has it that in the late 1500s, the famous Italian scientist Galileo dropped two cannonballs at exactly the same time from the top of the Leaning Tower of Pisa . . . . He believed that the cannonballs would land at the same time. . . . According to the legend, [he] proved to be right. . . . Galileo's experiment displays the basic laws of nature that govern the motion of falling objects." What experiment? A legend isn't an experiment, and science does not deduce laws of nature from legends. Just what did Galileo actually do? Why haven't Prentice Hall's writers tried to find out?

The teacher's edition offers a load of notes that are ridiculous. I've already cited some of these. Here are a few more:

• Page 23 displays an unrealistic graph (supposedly derived from a drag race) in which distance is plotted against time. The caption asks the student to find the acceleration, but he cannot do this because the book does not provide the necessary equation. A note to the teacher says flatly that the answer is "5 m/sec/sec" -- even though the acceleration is not constant. The correct value for the average acceleration is about twice as great as the value given in the note.

• Page 38: After directing the teacher to ask students why rolling objects "produce less friction than sliding objects," the writers say: "Student responses might include that wheels are round and move better and that there is less surface touching another surface." Perhaps, but those responses would be wrong. It would be nice if the teacher knew better.

• Page 50: In telling the teacher about Newton's law of gravitation, the writers say that masses must be stated in kilograms, distances in meters. Then they casually say, "G is the universal gravitational constant," giving neither its value nor its units.

• Page 66: "Pascal also proved . . . that air pressure can produce a vacuum." How did he ever do that?

• Page 85: Here, students must calculate how much work a woman does if she lifts her 100-newton suitcase and carries it for 25 meters, or (alternatively) if she drags it along the floor for 25 meters. A note to the teacher gives the right answer for the first instance, gives a wrong answer for the second instance, and then says that the "total work in both lifting and dragging is 2550 joules." But the woman performs one operation or the other, not both. The so-called "total work" is meaningless.

On page 86, in the chapter about work and power, a "Multicultural Opportunity" note to the teacher says: "During the 1960s, power referred to a political movement, often designed to gain rights for minority groups." This looks like a garbled effort to invoke the Black Power movement, though the writers seem afraid to say its name. Do they really think that the word power had no political meaning, or that the phrase political power didn't exist, until the 1960s? The writers have made a futile effort to invent a connection where none exists.

Perhaps the worst instance of pandering comes on page 89, where the teacher encounters a "Multicultural Opportunity" note about a black man named McCoy. The story is presented as if it were true, but it is obviously false and comes from an absurd source. [See "The Fake McCoy" in this issue of The Textbook Letter.]

On page 47 we see that blacks aren't the only beneficiaries of the writers' condescension. As if to show how little they know or care about people other than themselves, the writers make a miserably poor effort to concoct a "Multicultural Opportunity" note about gravity! The teacher reads that in some other parts of the world, the value of g (the acceleration due to gravity) differs slightly from the value measured at Washington, D.C. Imagine that! What the teacher does not learn is what this has to do with anybody's culture. Maybe the lesson is that foreigners have to be rather clever, in their own cute ways, to survive in places where a dropped object may take an extra millisecond to reach the ground. In any event, the writers wrongly call g a "force" -- and by giving a wrong value for g at the North Pole, they destroy their own account of how g varies around the globe.

As I inspected Motion, Forces, and Energy, I typed nine pages of notes about its faults and failures, and especially about the writers' ignorance of science. In the space available for this review, I have been able to give only a fraction of my observations, but I think I have said enough to make my point: Prentice Hall's book is not fit for human consumption.

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. His specialties are condensed-matter physics, the history of science, and science education.

return to top go to Home Page read our Index List, which shows all the textbooks, curriculum manuals,      videos and other items that are considered on this Web site support the work of The Textbook League contact The Textbook League by e-mail The Textbook Letter is published, copyrighted and distributed by The Textbook League (PMB 272, 40 Fourth Street, Petaluma, California 94952)