Conceptual Physics

Paul G. Hewitt


Hewitt Drew-It

Books & Videos

Photo Gallery

Yummy Links

Contact Info


Taxi Driver

Paul G. Hewitt -City College of San Francisco, San Francisco, CA 94112

March 1994

On my way to a recent NSTA meeting I got into a conversation with a taxi driver. When I told him I was a physics teacher, I got the same response I almost always get when I bring up physics with non-scientists. "You're a physics teacher? Not for me, pal. Physics was my worst subject in school. I hated it - couldn't hack it - couldn't do all the math." Isn't this the typical response most of us get? Something is wrong here.

Regrettably, too few students in high school ever take a physics course - usually some 10 to 20 per cent, depending on the school. But they all take biology. If the level of their biology course is classifying and distinguishing between plants, animals, and other life forms, then this makes sense. But biology nowadays depends on a knowledge of chemistry, which in turn depends on a knowledge of physics. Doesn't it make better sense that a science sequence begin with physics, followed by chemistry, and then biology? In most high schools, however, physics is taught last - mainly because of its greater reliance on math and its high priority on problem solving. Isn't something wrong here?

If high-level math and problem solving keep physics at the end of the science sequence, can't the emphasis of physics be changed to conceptual understanding so that physics can be taught in the 9th or 10th grade and begin the science sequence? And isn't there a serious weakness anyway, when physics is taught by the problem-solving route before students are well grounded in concepts? We're all acquainted with students in an English class who recite poetry without understanding it, and students in a chemistry class who memorize the periodic table but have no clue as to what chemistry is about. Is learning to solve physics problems without first learning physics concepts any different? Isn't something wrong when students can calculate the gravitational field of a planet but can't answer a qualitative question that asks for the difference in field strength twice as far from the planet? Their plugging and chugging skills have taken priority over conceptual understanding. Isn't something wrong here?

Solving physics problems may be a teacher's cup of tea, but it is an entirely different experience for students who have no grounding in physics concepts. Whereas the teacher sees problems in terms of the concepts used to solve them, the concepts-poor student sees problems in terms of their situations - there are "pulley problems," "inclined plane problems," "pulleys-combined-with-inclined-plane problems," and so forth. Problem solving becomes a fitting of mathematical puzzles into the textbook's world-of-its-own problem sets. Students who are trained to do this well, sadly, are under the impression that they are learning physics. What's even more regrettable, some of their teachers have the same impression. Hasn't research indicated time and again that students who learn physics via the problem-solving approach are woefully deficient in their understanding of concepts? Nevertheless problem solving is the preferred method of physics instruction. It is expeditious, for lecture notes need be little more than a selection of problems that will fit class time. Besides, it's fun to solve problems and demonstrate their solutions. Physics teachers love problems perhaps more than English teachers love crossword puzzles. Isn't something wrong here?

Another reason for the problem-solving orientation of physics courses is the failure to distinguish between physics and math. The belief that physics is applied mathematics is so strong that many parents complain if their youngsters in high school are not crunching numbers. They see a concepts-based course as a substitute for the "real thing." Equations in the concepts-based course are guides to thinking about relationships, rather than recipes for crunching numbers. Numbers, they say, are what real physics is about. No distinction is made between the application of physics concepts and physics concepts themselves. The distinction, admittedly, is blurry compared to easier-to-make distinctions. Consider the distinction between grammar and physics as an example. If a physics teacher emphasized communication skills and purported that physics is best be taught in the context of language and syntax, parents might be somewhat bothered. If this emphasis bogged down the course so that most time was spent on mechanics, with only a brief touch of electricity and magnetism, and no time at all for modern physics, parents would complain loudly. Why? Because everybody sees the clear distinction between grammar and physics. Despite the importance of grammar, they'd complain that the sole year of physics ought to focus on physics - that grammatical deficiencies ought to be addressed in any of several English classes rather than in the precious solitary physics class. There's no doubt that something is wrong here.

Now consider the comparable situation where a teacher has a similar obsession with math, and spends primo course time on the tools of physics rather than the concepts of physics themselves. Suppose so much time is spent on significant figures, exponential notation, coordinate systems, graphical analysis, and the sharpening of algebra and trigonometry skills for the end all of problem solving that the course bogs down in mechanics, barely touches electricity and magnetism, and never gets to modern physics. Parental response? Acceptance! Why? Because the tools of physics are mistaken for physics itself, which stems from not distinguishing between math and physics. Most people still think that physics is math applied to word problems. Isn't something fundamentally wrong here?

So what is physics, if not a collection of mathematical word problems? To us in the physics community, one of many answers is that physics is that found between the covers of the three volumes of The Feynman Lectures on Physics - each volume without a single word problem.1 Feynman develops the concepts of physics and applies them to the everyday world, not as a basis for solving problems, but as a way of seeing the order and regularity in the world. Is not science a continuing formulation of the rules by which nature operates? And is not physics the study of the most basic of these rules?

We know that we cannot appreciate a chess game without knowing the rules of chess or enjoy a sports event without knowing the rules of the event. So it is with nature. We cannot fully appreciate the physical world about us without knowing its rules. Just as our life experience is enriched by knowing what to look for in art, and what to listen for in music, so it is with the physical world. The richness in life is not only seeing the world with wide open eyes, but knowing what to look for. A good physics course points out what to look for - shows that all the seemingly diverse phenomena about us are tied together by surprisingly few rules - rules that are beautiful in their simplicity. With an understanding of Newton's Laws, for example, we see that a tossed baseball, an orbiting space shuttle, and planets circling the Sun all follow the same simple rules. With an understanding of energy conservation we see not only mechanical devices differently, and chemical and biological processes differently, but see all sports differently, and see a pounding surf at the beach differently - in much the same way a composer hears music differently and an artist sees the relationships between light and color differently.

Time is precious to both taxi drivers and physics teachers. Just as wisdom is knowing what to overlook, good teaching is knowing what to leave out. When something is left out, something more important can be put in. By leaving out remedial math and minimizing problem solving, students have the time to learn classical through modern physics conceptually. Instead of training in problem solving, they learn to articulate concepts, to distinguish between closely related ideas, and to see where concepts do and do not apply to examples in the everyday world. This substitution of concepts in place of problems is an enormously beneficial trade when it occurs at the beginning of a student's high-school science experience, for then the study of the other sciences is richer. An early physics-concepts course can prove so popular that a follow-up senior year problem-solving course should be well attended.

If that physics course our taxi driver took had had this orientation, he might say to us, "You're a physics teacher? Wonderful! I loved physics when I was in school, because it changed the way I see things. I wasn't too good in math, so I didn't continue with the follow-up course, but I sure enjoyed the physics course I had." Something, at last, is right here.

1. The Feynman Lecture on Physics, Richard P. Feynman, Ralph B. Leighton, and Matthew Sands, Addison-Wesley, Reading, MA, 1963.

Good Energy!

        Paul G. Hewitt