The Unabashed Academic

20 March 2011

On service courses

In physics departments, a lot of the students we teach are not going to be physics majors.  They are going to be engineers, chemists, computer scientists, biologists, and doctors.  Everybody (that is, all physicists) agrees that physics is good for all future scientists since physics is the basis of all other sciences – at least that’s the way it seems to physicists. We tend to be reductionists.  That is, we build everything up from fundamental low-level principles.  Thus, in principle, quantum mechanics is a consequence of quantum field theory, chemistry is a consequence of quantum mechanics, biology is a consequence of chemistry, and medicine and social science are a consequence of biology.  Therefore, every science is based on physics.  Of course none of those connections (even the first) are filled in yet – or are likely to be filled in for many years, if ever.  But that’s a topic for another essay.  If those “in principle” reductionist connections are not why we teach physics to other scientists, what is?

I think that there are still lots of good reasons for other scientists to take physics.  The first and most obvious is that physics actually plays a role in the actual practice of all those sciences.  Chemists need to understand electricity and quantum physics, biologists need to understand fluid flow and energy, and doctors need to understand forces and torques as parts of their knowledge collection.  But more important than the specific bits of physics is the “physics way of thinking”.

The core of the approach that physics takes to science is that of finding and reasoning from a small core of fundamental principles.  And the deeper and more advanced we go in physics, the fewer and more powerful the principles become.  At the macroscopic level, we learn conservation of energy and momentum and they are fundamental principles that allow us to think about and solve many complex situations.  At a more advanced level, the fundamental principles become that our laws of physics should not depend on where we are or when we apply them.  This invariance with respect to space and time turns out to imply energy and momentum conservation.

One result of this “push for principle” in physics is that we tend to simplify.  Einstein said, “Physics should be as simple as possible, but not simpler.”  We seek the simplest possible problem that illustrates the application of the principle we are trying to teach.  I call these touchstone or toehold problems.  Once we understand these simple examples thoroughly, then more complex situations can be built around them.  The toehold examples provide starting points, ways of going forward or of organizing what we know in order to make sense of the complexity. 

We spend a lot of time working on the simple case of a mass attached to a spring since this provides us with a way of thinking about any oscillating system.  The core ideas behind oscillation are restoring force and inertia.  The is some stable equilibrium of the system such that when the system is deformed away from it, there is a force that attempts to pull it back to the equilibrium point.  Typically, that force gets stronger the farther you get from equilibrium and vanishes at equilibrium.  As that system is pulled back towards equilibrium, it starts going faster.  When it reaches equilibrium, the restoring force vanishes.  But at that point it is moving and has inertia.  Since there is no more force to stop it, it keeps going, goes past its equilibrium and we start all over.  This pattern can be working out in detail for the mass on a spring and provides the basis for describing damped oscillations, driven oscillations, coupled oscillations and resonance, as well as (perhaps surprisingly) a basis for the theory of motion of protons and neutrons in a nucleus or the theory of light in quantum field theory.

Besides this “drive for the simple”, physics thinking has a number of other characteristics such as looking for coherence, thinking about physical mechanism, taking multiple ways of looking at things, and making the connection to everyday experience.  (This last sometimes needs some refinement of our everyday experience to reconcile it with the science we have developed.)  There are valuable tools that we commonly use to achieve these ends such as doing dimensional analysis or considering limiting cases.

In an attempt to make physical thinking more explicit in our traditional service courses, my colleagues and I at the University of Maryland have spent the past decade learning about our biology clients in our algebra-based service course and refining the course to help them learn to strengthen their scientific reasoning skills.  [The method and results are laid out in our paper, Reinventing College Physics for Biologists: Explicating an Epistemological Curriculum , E. F. Redish and D. Hammer, Am. J. Phys., 77, 629-642 (2009).]  We had good success with this class.  On standardized mechanics conceptual tests (FMCE) we get much better pre-post fraction of the possible gain ( ~ 0.45-0.50) than in traditional classes ( ~ 0.15-0.30), and we get strong gains on our Maryland Physics Expectations (MPEX) survey, something not seen in most traditional classes.  

Anecdotal comments from students are also often positive and supportive (though they sometimes complain that there is too much hard work for a 100 level class).  Many students have said that the course changed the way they think about science for the better. (Some anecdotes are reported in the above-cited paper.)  But a recent comment from a student brought me up short. 

The week before the beginning of the second term, a student who had been in my first semester class came by to tell me I would be seeing him and his two friends from the class again.  He said they had enjoyed the class very much, worked together on the homework (as I had encouraged them to do), and felt they learned a lot.  As a result, they signed up for the second semester right away, choosing my course over some competing courses in their major.  He added that they wanted to take my course, despite the fact that they were biology majors and therefore it wasn’t of much relevance for them.

Well!  Despite the fact that I had thought carefully about what might be useful for biologists in their future careers, and focused on developing deep scientific thinking skills, it suddenly became clear that I had failed in an important part of my goal.  I had managed to teach some good knowledge and good thinking skills, but I had not made the connection for my students to the role of that knowledge or those skills in their future careers as biologists or medical professionals.  The occasional problem I had included with a biological or medical context did not suffice.

I now see that often I taught my principles and simple examples without making a real connection to show how those principles imbed in complex situations.  This can make my basic principles and the problems I give seem more like puzzles and games than ways of parsing a more complicated problem. 

I therefore propose we who are delivering service courses for other scientists – and I mean mathematicians, chemists, and computer scientists as well as physicists – ought to measure our success not just by the scientific knowledge and skills that our students demonstrate, but by their perception of their value to themselves as future professionals.  We can tell ourselves, “Well, they’ll see later how useful all this is,” and they might, but that is really wishful thinking on our part.  If our students see that what we provide is valuable now, they will maintain and build on what they have learned in our classes.  Otherwise, it is likely that what we have taught will fade and our efforts will have been largely in vain.

 For years I have been asking my students an extra credit question on my final exams, “Have you learned anything in this class that you think will be of any use to you in five years?  If so, what?  If not, why not?” (5 points for any thoughtful answer)  Up to now I have been looking at the results with interest and amusement.  I now intend to take those answers much more seriously and will use them as a significant measure of what I see as overall success in my service courses.


  • For mathematicians, you are better off showing them the beauty of the models, without trying to pretend it is useful to them. Mathematicians value beauty over utility most of the time.

    For computer scientists, you'll have a very hard time convincing them that physics is useful to them, unless they are really computer engineers and want to learn some electronics as well. Physics and physics-style thinking is not really that useful to computer scientists.

    Chemists should be an easy sell—they work with more complex systems than physicists do, and so need to use more simplifications in their models, but the style of thinking is very similar.

    Biologists have vastly more complicated systems, and their science is data-driven, not model-driven. Thinking like a physicist does not get you very far in biology.

    By Anonymous Anonymous, at 1:35 PM  

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