Reflections on Matter and Interactions

I’m teaching introductory mechanics for the umpteenth time, using the Matter and Interactions curriculum, as we have for a while. This is going to be my last time teaching out of M&I, though, because last year the department decided to switch to a different book. Starting this winter term, we’ll be using Halliday, Resnick and Walker.

My physics blogging over at Forbes tends toward the contemplative anyway, for a variety of reasons, but knowing that this is the last time through M&I has had me thinking even more along those lines. Thus, recent posts on really simple physics and what it means to say something is fundamental and missing pieces. A detailed discussion of the pros and cons of the book is a little too inside-baseball for Forbes, though, so I’ll blog about it here.

First and foremost, I should say that the switch away from M&I to HRW is not one I would’ve made. I like M&I a lot, and enjoy teaching from it. Several of my colleagues really detest M&I, though, and haven’t gotten any happier about it over the years, so I understand the reason for the change. I’m really going to miss this book, though I suspect that the things I really like about it are also major factors contributing to my colleagues’ dislike of it.

The first thing I like, as mentioned in the missing pieces post, is that the curriculum has a very strong and definite narrative to it. They’re coming at the subject matter of introductory physics from a very particular point of view, and the sequence of topics and their presentation are carefully tailored to reflect and reinforce that point of view. It’s a very physicist-y way of looking at things, and emphasizes computation, always starting with discrete elements and repeated summation.

This sense of narrative is both good and bad– the book has a nice flow, and constantly reinforces its main ideas, but it requires some buy-in. And if you can’t adapt to their viewpoint, teaching from it is very awkward– the order of topics in electromagnetism initially struck me as strange, and I tried to do an on-the-fly re-ordering of the material the first time I taught it, with very limited success. In subsequent terms, I made more of an effort to go with the book as it was, and that worked much better.

The particular structure they choose also leads to some limitations in the material they cover. From the very first chapter, they emphasize the use of three-dimensional vectors for all physical quantities, using a very consistent convention for the axes where y is vertical and x and z horizontal. This choice of fixed coordinate system makes it awkward to do the traditional block-on-an-inclined-plane problems, though, where the key step is choosing to deal with coordinates defined by the plane, rather than by gravity. The end result is that they basically don’t do those problems at all, which is cause for rejoicing for some students, but also misses the key idea of the arbitrariness of the choice of axes.

They also have a weirdly perfunctory chapter on collisions, which sets up the difference between inelastic and elastic collisions, but doesn’t provide useful problems regarding the latter. Again, I think this is rooted in the consistent use of three-dimensional vectors, because elastic collision problems in more than one dimension are really hard to do at the intro level. (In the HRW-type curriculum, I usually skipped 2-d elastic collisions due to time constraints; with M&I, I often skipped the entire collision chapter, because they don’t get anything out of it but a couple of vocabulary words.)

On the other hand, it opens up other classes of problems, and they do more with air resistance than most texts, because those kinds of problems can only be solved numerically. As I said in the missing pieces post at Forbes, the complex-systems problems are great, and in the electromagnetism course they do some rally cool stuff using a microscopic picture of current that I haven’t seen elsewhere. So, you know, you win some, you lose some.

So, I like the narrative aspect, but it makes the text harder for a lot of faculty to adopt, or perhaps “adapt to” would be a better term. If you don’t find their viewpoint congenial, and aren’t able to fully buy into it, you’ll end up fighting against the book a lot of the time, and that makes for a frustrating teaching experience.

The other big factor that I like that puts some people off is that it doesn’t look like high-school physics. We used to teach out of HRW and its isomorphs, back when I started at Union, and I noticed a pattern in those classes where the students with the best preparation coming in would follow a particular bad trajectory. The first 5-6 weeks of the intro course on the HRW template looks almost exactly like a good high-school class: kinematics in 1-d, Newton’s laws, projectile motion, block-on-a-plane, etc., so students who had a good class in high school could pretty much coast on what they learned in that previous class. As a result, I’d see their study habits and general engagement drop off. And then when we hit them with genuinely new stuff in work and energy– dot products and integrals– they’d go all to pieces, because they’d fallen out of the good habits that would let them grapple with and power through new material.

M&I breaks that by not looking at all like high school physics. They start off with momentum– in the relativistic form, even– and everything is in three dimensions right from the get-go. Even the language used to talk about the physics is different– they don’t discuss “Newton’s 2nd Law” but rather “The Momentum Principle,” and frame the discussion not in terms of formulae for particular special cases, but iterative application of general principles.

This is confusing, even for the good students, and they can’t fall into coasting on their high-school classes. Which reduces the problem of study-habit atrophy, forcing them to stay more engaged even in dealing with material that they’ve seen before.

The down side of this, of course, is that it’s confusing, and that leads to a lot of questions from students, and a fair number of complaints. Which can be kind of a hassle, from the faculty side.

My personal feeling is that the extra confusion is actually a good thing, on balance. Others see it as being a sign that the curriculum doesn’t work for our students. There’s also some concern that students without a good background are at a big disadvantage, but I don’t really buy that. My impression over umpteen iterations of the class is that the least prepared and most confused students are no more bewildered under M&I than they were with HRW and isomorphs, but the students with good preparation are more confused, and more vocal about that confusion. I think they ultimately end up “getting it” at least as well as they did under the more standard curriculum, but they need to work at it more, and that will be to their ultimate benefit.

So, as I said, I’m happy teaching from M&I and wouldn’t switch books at all. I definitely wouldn’t pick HRW as my first choice of new text. But I understand that others have a strong negative feeling about M&I, so I’ll go along with that. There are even some benefits– we’re closing in on the point with my current approach where I would need to blow up my notes and start fresh just to keep myself from getting bored, and this forces my hand. And it will make it much easier to crib materials from the Colorado PER group (which I’ve been doing already, but carefully selecting problems and altering wording to fit the M&I language). And while I think HRW is about the most boring choice we could’ve made, that’ll force me to find new ways to keep the class from looking so much like high school physics that the students get bored and tune out. I’ve got some thoughts along those lines already.

Still, I’m going to miss teaching out of M&I. It’s been fun, and I’ve learned a lot about intro physics from taking this different perspective on it.

Comments

  1. #1 AJD
    November 12, 2016

    Do you think that you will find yourself “fighting against the book” when you switch to HRW? Will you continue to include computation in the intro classes, even if the textbook doesn’t support it?

  2. #2 Chad Orzel
    November 12, 2016

    I probably won’t try to do computation with HRW, because it’s very time-consuming to teach, and we’re always under time pressure. There’ll be a bit of fighting against the book in that the HRW format lends itself much more to formula-hunting, and I really hate that. My plan is to use a lot of video analysis of real(ish) problems, something I’ve done a bit of with M&I, but struggled a little to incorporate because so much of the good video stuff that’s out there is tailored for more HRW-like curricula, with lots of inclined planes and so on.

  3. #3 dean
    November 12, 2016

    Only tangentially related comment: back in 1974 I had to buy a yellow(ish) physics text by Halliday and Resnick, and I used it for 3 semesters. I still have it, and just checked the faint price that is still inside the front cover: $18 and some change.

    Usinflationcalculator dot com tells me that something that cost $20 in 1974 would cost about $100 today. Looking at the current book prices in your link, it seems you in physics have some of the same issue with rapidly increasing textbook costs we do in statistics, but IMO it’s still a little worse for us.

  4. #4 Omega Centauri
    November 12, 2016

    I couldn’t locate it, but when my son had intro physics at UC Merced, the textbook included a license to an online homework app “Mastering Physics”. The license was only good for 1 student one semester, which meant you couldn’t use a used book. And the price for the combo was over $3000, which I thought was a horrible financial imposition on the students.

    The actual homework app was interactive, and if you got the wrong answer, it would tell you and let you retry as many times as needed. That could easily have been abused by students who just wanted to shotgun guesses at it until they got the correct result.

  5. #5 Omega Centauri
    November 12, 2016

    Opps, that was $300, it looks like I typed an extra zero.

  6. #6 enl
    November 13, 2016

    Welcome to the future of textbooks. There are a number of reasons for the change, but in my opinion, it is just a more efficient and lower cost version of the new edition every year model. The publisher has a reliable income stream. If there were options with regard to publisher, this could backfire by making it easier to change texts due to the lost incentive to stick of the used book option, but a quick look at the textbook publishing world will show a very, very limited set compared to 20 years ago.

    Associated with this is the push for online materials (no matter what the quality) in many environments, which, again, has the benefit of reliable income stream. The school district where I like tossed all paper books, bought chromebooks, and signed for 5 years of licenses for online delivery. If the kids don’t have an internet connection, no book. The annual is about half of a new paper text. The paper text lasted 5 to 10 years, typically, so it is a major financial hit over time, but not all at once, so the cost cutters look good.

  7. #7 lyle
    November 13, 2016

    All be it it is a two year course did they consider Feynman Lectures on Physics? IMHO it is the best intro physics text book, all be it does not come with a lot of problem sets.But in the past it has been criticized as being to intense for most colleges into series as well, (since it was taught at Cal-Tech)

  8. #8 Bruce Fowler
    United States
    November 13, 2016

    I am going to make a wild conjecture that your calculus-based, Freshman Physics population is not overwhelmingly engineering service course freshmen. In my experience, they vastly prefer Halliday and Resnick in any of its variants. I also have to admit to being rather on the other side of the matter, I suspect. My favorite Freshman Physics text has always been the Schaum’s Outline, followed in the more recent past by Jerry Marion’s book. This was based on a valuation of the merits of the text as its endurance: how well does it serve as a reference and memory aide in the years after the course? With the GEN Y penchant for discarding texts immediately after the exam, this is probably dated.

  9. #9 Chad Orzel
    November 13, 2016

    Actually, our intro course is mostly an engineering service course. I do think those students would be happier with a more HRW-style book, but then, they would’ve been happier with an even more formula-driven approach back when we used HRW and isomorphs. I think that, if you fully buy in to the approach, M&I has a lot of potential to appeal to engineering students, particularly those who are good at programming.

    Textbook costs are just absurd, bordering on obscene. Especially given how little most students use the books. I’ve run into that regarding the book for my Winter term course, too– a single modern physics book costs almost $200 new. It’s almost enough to make me consider doing without and just providing super-detailed lecture notes.

  10. #10 CCPhysicist
    November 14, 2016

    First, those articles on F—- are now unreadable with side bars and an intrusive ad that includes audio. I only stayed long enough to notice your diagram of tension and compression (normal) forces, which belongs in every book. We should admit that matter is made of atoms, which can only help when you get to thermo because it enables discussion of energy “lost” to friction as a transfer to internal energy long before you get there.

    However, I also see the possibility of confusion. Put that model of a surface at an angle, and it would seem that the surface force is not normal to the surface unless you impose some constraints on it. And a rope has mass, to it won’t be straight if it is at an angle. This is ultimately good for future engineers, but dangerous. And they — as well as physics majors — need to know how to choose the appropriate coordinate system for a given problem rather than imposing constraints.

    Two questions.

    Did you look at any of the open texts? It would be great to get the faculty of a school like yours on board to add even more voices to the defacto peer review board. The one we are looking at seems to be a free HR-style text except it has a “vectors first” approach. I think you can also have them buy a homework system separately.

    Have you looked at the changes in the AP physics curriculum? Those students might prefer an inquiry based approach with the kind of modeling you want them to do.

  11. #11 Bruce Fowler
    United States
    November 14, 2016

    I agree, based purely on your discussion and a cursory review of on-line advertising, that I would prefer the M&I approach if I had the freedom to select. You don’t have that nor, I understand, do many universities accord that to contemporary faculty. I used to do my own lecture notes and share them with my students but that was mostly graduate courses. In those days we barely had xerox machines and they were zealously guarded by administrators wary of irresponsible faculty and grad students. My colleagues who still get to teach assure me they have no time for such and have to rely on textbook publishers’ bennies, which include learning forbidding “powerpoint slides.” It sometimes seems the modern university is dedicated to preventing learning.

  12. #12 CCPhysicist
    November 15, 2016

    When I first read and commented on this post, I fell into the narrative that the people teaching a course are the best people to ask about how it works. Yes, the comfort level of the instructor does affect the classroom climate, but what really matters is how physics majors do in their first real physics classes, the ones they take after yours. Did you get solicit any feedback from those faculty about the strengths and weaknesses of the students coming out of your course?

    Similarly, have you approached the engineering faculty to see what they see as the strengths and weaknesses of the students that show up in their first engineering mechanics class, and how those might have changed since you changed books? If not, you might ask them to start noticing any changes a year or so from now.

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