Friday, May 31, 2013

Rounding Off the Cow

In the October 2012 issue of the American Journal of Physics, Dawn Meredith and Jessica Bolker published an article about Rounding Off the Cow: Challenges and Successes in an Interdisciplinary Physics Course for Life Science Students (Volume 80, Pages 913-922). The article is interesting, and much of the motivation for their work is nearly identical to that of Russ Hobbie and I in writing the 4th edition of Intermediate Physics for Medicine and Biology. They focus on an introductory physics class, whereas Russ and I wrote an intermediate level textbook. Nevertheless, many of the ideas and challenges are the same. Here, I want to focus on their Table 1, in which they list topics that are emphasized and deemphasized compared to standard introductory classes.

Table I. Changes in topic emphasis compared to standard course
Semester 1Semester 2
Included/stressedKinematicsHeat transfer
DynamicsKinetic theory of gases
Static torqueEntropy
EnergyDiffusion, convection, conduction
Stress/strain and fractureSimple harmonic motion
Fluids (far more)Waves (sound, optics)
Omitted/de-emphasizedProjectile motionHeat engines
Relative motionMagnetism (less)
Rotational motionInduction (qualitatively)
StaticsAtomic physics (instrumentation)
Newton’s law of gravitation
Kepler’s laws

How does this list compare to the content of IPMB? We don’t stress kinematics and dynamics much. In fact, most of our mechanics discussion centers on static equilibrium. Interestingly, Meredith and Bolker emphasize static torque, which is absolutely central to our analysis of biomechanics in Chapter 1. Rotational equilibrium and torque is what explains why bones, muscles and tendons often experience forces far larger than the weight of the body. It also underlies our rather extensive discussion of the role of a cane. We discuss mechanical energy in Chapter 1, but energy doesn’t become an essential topic until our Chapter 3 on thermodynamics. We agree completely with Meredith and Bolker’s listing of “stress/strain and fracture” and “Fluids (far more)”, and I second the “far more”. Our Chapter 1 contains a lot of fluid dynamics, including the biologically-important concept of buoyancy, the idea of high and low Reynolds number, and applications of fluid dynamics to the circulatory system.

The time allotted to an introductory physics class is limited, so something must get deemphasized to free up time for topics like fluids. Meredith and Bolker mention projectile motion (we agree, it is nowhere in IPMB), relative motion (not crucial if not covering relativity), and rotational motion (we don’t emphasize this either, except when analyzing the centrifuge). I don’t really understand the omission of statics, because as I said earlier static mechanical equilibrium is crucial for biomechanics. They deemphasize collisions, and so do we, although we do discuss the collision of an electron with a photon when analyzing Compton Scattering in Chapter 15. Newton’s law of gravity and Kepler’s laws of planetary motion are absent from both our book and their class.

In the second semester, Meredith and Bolker stress heat transfer (convection and conduction), the kinetic theory of gases, and entropy. Russ and I discuss all these topics in our Chapter 3. Diffusion is a topic they emphasize, and rightly so. It is a topic that is typically absent from an introductory physics class, but is crucial for biology. We discuss it in detail in Chapter 4 of IPMB. Meredith and Bolker list simple harmonic motion among the topics they stress. We talk about harmonic motion in Chapter 10, but mainly as a springboard for the study of nonlinear dynamics. Much of the analysis of linear harmonic motion is found in IPMB in an appendix. Finally, they stress waves (sound and optics). We do too, mainly in our Chapter 13 about sound and ultrasound; a new chapter in the 4th edition.

Topics they omit or deemphasize in the second semester include heat engines. We barely mention heat engines at the end of Chapter 3, and the well-known Carnot heat engine is never analyzed in our book. Meredith and Bolker deemphasize magnetism and magnetic induction. As a researcher in biomagnetism, I would hate to see these topics go. Russ and I analyze biomagnetism in Chapter 8. However, I could see how one might be tempted to deemphasize these topics; biomagnetic fields are very weak and do not play a large role in either biology or medicine. I personally would keep them in, and they remain an important part of IPMB. They do not stress “Atomic Physics (Instrumentation)” and I am not sure exactly what they mean, especially with their parenthetical comment about instruments. We talk a lot about atomic physics in Chapter 14 on Atoms and Light. Finally, Meredith and Bolker omit relativity, and so do Russ and I, except as needed to understand photons. We never discuss the more traditional phenomena of relativity, such as the Lorentz contraction, time dilation, or simultaneity.

Some topics should get about the same amount of attention as in a traditional class, but with slight changes in emphasis. For instance, I would cover geometrical optics, including lenses (when discussing the eye and eyeglasses) but I would skip mirrors. I would cover nuclear physics, but I would skip fission and fusion, and focus on radioactive decay, including positron decay (positron emission tomography).

I think that Meredith and Bolker provide some useful guidance on how to construct an introductory physics class for students interested in the life sciences. Russ and I aim at an intermediate class for students who have taken a traditional introductory class and want to explore applications to biology and medicine in more detail. Our book is clearly at a higher mathematical level: we use calculus while most introductory physics classes for life science majors are algebra based. But for the most part, we agree with Meredith and Bolker about what physics topics are central for biology majors and pre-med students.

1 comment:

  1. The take home message is that you can not cram all of physics into one course. Which topics offer the most useful sets of tools to the students? Answer: it is not the topics themselves that are important, but how they are approached (derived from fundamental theorems) and how they are applied. This is the heart of what physics truly is: how to set up a problem and apply it in appropriate situations. In your classes, for example, you took the time to explore different possible applications by offering a wide variety (from many areas of science) of examples. While the text book is an excellent source for the student and the teacher - the real magic happens at the board when the Professor picks up his drawing pen.