Saturday, March 10, 2007

The place of Newton's Laws in the physics curriculum

As you may know, I've just written a manuscript for a book about Newton's Laws of Motion. The inspiration for today's post was my deepening realization that in one sense at least, this project sails against the prevailing winds of postsecondary science education. By this I mean that the book does not attempt in any way to connect the core ideas to issues of importance in the world. Everyone in physics is trying to do that today, not just in the liberal arts colleges but also in universities, with courses on Physics for Future Presidents and so on. Let me say that I think the prevailing winds are blowing in a good direction, and I foresee myself doing a lot of work that goes with the flow. But let me also try to draw a distinction here. There is 'commodity physics' and then there is 'deep physics.' Commodity physics includes topics like lenses, heat conduction, circuits, and even to some extent energy. This stuff is a commodity in the sense that just about anyone can learn it, and just about anyone can teach it. And, since it doesn't take long to learn, having learned it you are in a position to apply it all over the place. This is where the textbooks are going.

But the Laws of Motion are not a commodity; they're precious metal. They are buried deep, hard to reach; those who catch a glimpse of them experience awe, perhaps even mania.

There are very different reasons to study physics "as a liberal art." One reason can be for the citizenship stuff, and in that case you end up pushing ideas such as problem-solving and rates of change; and you end up linking topics such as heat conduction to applications like R-values for home insulation. Great; worth doing. But the other side of the liberal arts is the great ideas, and the stretching that we do to reach them, and the way they stay with us for life. Newton's Laws of Motion are a masterpiece. Teaching them so that you can connect them to social problems is like teaching Hamlet so that your graduates can be impressive at cocktail parties.

A clue to the distinction I'm trying to make between Newton's Laws and other parts of physics may be found in the fact that it is not very easy to invent good examples of applying the Laws of Motion in a technology or industry setting, whereas for topics like energy or circuits it is effortless to do so. It's as if one were to try to write an essay question along the lines of, "How would Hamlet have handled the Cuban Missile Crisis?"

I wish I didn't have to make this kind of distinction between commodity physics and deep physics, but the difficulty and subtlety of the Laws of Motion force you to make a choice. The views are from the top, and it takes a long time to get there.

Lately I've been having the radical thought that Newton's Laws should be removed from most introductory physics courses. You're probably laughing out loud right now, but bear with me for a moment. If you were to suggest this idea to a physicist, I bet he or she would object in the following way: "Are you crazy? It's all *based* on Newton's Laws for God's sake!" But I say, (A) If the Laws are so important, then why aren't you more upset that so few of your students are learning them? (B) If it's really "all based on" Newton's Laws, then why don't students' difficulties with the Laws doom them for the rest of the introductory year? (C) Energy and momentum have central roles in contemporary physical theories, but force does not; so can't we just get over the historical blip that was 1687-1926? (D) Remember, I'm not touching the curriculum for physics majors or engineers, so try to stay calm. (E) Let's take a careful look at the curriculum and see who actually has to know what. Yes, doctors have to know about forces because of structural anatomy and muscles; but when they do this work do you really think they're using what *you* taught them? They forgot all that a long time ago. They're just using everyday intuitions about force; and everyday intuitions are fine for everyday purposes.

Once you remove Sir Isaac from the non-physics-major curriculum, you can offer non-majors a course specifically about Newton's Laws. This is more like a course on Hamlet, in that students take it not for what they can do with it, but for what it adds to their inner lives. And notice that with a whole semester to spend, we can make another radical move, which is to really teach non-physics-majors the Laws: not a cartoon version of them but the full vector dynamics, the way it's done in my book. I can report that this works, because I actually taught Physics 1 last fall to a class of mostly non-majors using a draft of my book, and it was great. I had more success in getting the core ideas across than I ever did before, and that includes my experiences teaching Physics 131 at Grinnell College and TA'ing Physics 7A and 8A at UC Berkeley. But the pace was radically slow by the usual standards; and even at that slow pace, if I'm honest I have to admit that the end result was that the students' understanding was fragile. After such herculean efforts on everyone's part, I could still trip them up at will with certain conceptual questions. It was the failure mixed with the success that led me to wonder if more would be gained than would be lost by removing this material from the introductory physics curriculum altogether.


Larry Berger said...

Am I right to be bothered by the word "commodity"? I know you are trying to provoke, but I wonder if you mean something else, and if you risk people surfacing their own claims of intrinsic beauty and deep meaning in the ways of lenses.

I'm struggling for a substitute. It certainly isn't applied vs pure. Perhaps it is a prose/poetry type of distinction. Your deep/surface metaphor worked well (and may itself work against the term "commodity" if the precious metals are traded on the commodities exchanges). Am I right to think that the two things you want in the term are "core vs. peripheral" and "elegant and intrinsically inspiring vs. practical and relevant?"

Alan said...

I don't think we should teach "commodity" physics, because I don't think that is what students think is relevant. It is possible to teach the elegance of physics - parts of the Feynman lectures, for example - and the excitement of the years 1896 - 1945 in physics, and also relate it to the dropping of the atom bomb, to use just one example. In my experience, students are much more interested in those kinds of social justice issues than they are in how an automobile works (unless you are explaining that in relationship to global warming, which students, at least my students, really care about).

We do teach too much breadth and not enough depth. Even more troubling is that when you add the social justice aspects, you have even less time to deal with the physics (or biology, or chemistry). But it does connect the science much more to the students' lives.

Mia said...

JZ, I appreciate the honesty and stream of consciousness with which you present your thoughts and dilemmas. Allow me to respond in kind, with the warning that I am a sociologist who specializes in social and cultural aspects of physics education.

First, there are several studies in my social science world that might inform your theories. Education studies, for example, by Andy DiSessa (UC Berkeley) or Ricardo Nemirovsky (UCSD) about how kids understand (or not) Newtonian mechanics. Or sociological studies that demonstrate that good-looking people tend to get hired and promoted at rates much greater than the uglies. I just want to point out here that you are not alone in forming or testing these kinds of hypotheses.

Second, I advocate more physicist - social scientist collaborations. On one of my own projects, for which I partner with a biophysicist, we are researching the effectiveness of project-based learning in physics and math on women in four undergraduate engineering programs. These students are getting great educations and know they'll have high-paying management positions when they graduate--which I think falls into your commodity physics argument--, but I do worry about their souls. Words like "beauty" and "evanescence" are not part of their vocabularies when describing their learning. I hail from a liberal arts background, so my view is admittedly biased.

Third and finally, I have a friend who just finished his own manuscript of an introductory physics text. It contains 50+ physics-related limericks. Do limericks count as poetry and beauty that might pop out to students to enhance their learning? I'm really not sure. Should we be writing a grant to study the possibility of this phenomenon?

Susan said...

First thought. It seems to me that the challenge, above all, is to teach a great idea in ways that students come to feel its power and beauty in their bones. In other words, the aesthetics of the idea are the hardest, but perhaps the most useful thing to convey. This is very different from teaching concepts through illuminating applications, which I think tends to constrain more than liberate, or at least inhibits the learner from taking the idea and letting it ramify through a whole range of inquiries and concerns.

dr. dave said...

The idea of a "Course about Newton's Laws" isn't terribly far from what I try to do for my liberal arts students. I have the luxury of being the only physics guy at a school with NO phys/chem/bio majors, so I don't have to worry too much that the students aren't getting this or that bit of technical knowledge.

I take a much more historical and literary approach to physics in my liberal arts classes. In "Foundations of Physics", for example, we begin the topic of Galileo and acceleration by reading his dialogues. We begin the section on Newton's Laws by reading them in the original Latin, and translating them word-by-word... cognate-by-cognate. (It's really quite easy with a little prompting for the short words.) We do problem solving as well, but we never START with the equations. What these students do best is read and analyze, so we always start there.

So in some sense, I agree that the TECHNICAL usefulness of Newton's Laws is fairly minor for most students of physics. But as far as their role in the history of physics and the so-called "Scientific Revolution", I think they are conceptually indispensible.