Wednesday, April 16, 2014
Why Biology, Pre-Med Majors Can't Do Physics
Once again the issue of Life sciences majors' inability to do physics has come to the fore, now in a follow-up discussion appearing in the April issue of Physics Today (pp. 12-13). This follows a detailed article ('Reinventing Physics for Life-Sciences Majors' ) that appeared in the July, 2013 issue. I had dealt with the latter article in an earlier post: http://brane-space.blogspot.com/2013/08/life-sciences-majors-and-physics.html
As I noted therein:
Physics stresses reasoning from a few fundamental principles, and generally expresses those principles in terms of mathematical laws, i.e. Newton's Second law of motion, F = ma. Biologists, meanwhile, focus on structure- function relationships and rarely stress quantitative reasoning. There is also an enormous amount of memorization which students also think they can bring to physics - but are sadly mistaken.
These points were again highlighted in the Physics Today letters. Among some of the observations made were the following by a lecturer in calculus physics and algebra-based physics at San Diego State College:
"The biology majors I have taught are comfortable with memorizing and reproducing. They have never learned to solve problems. They have a fantastic memory power and there is no way to make use of it in a physics course."
As an example consider the sample problems below from a typical course in first year college physics:
1. A 1.8 m (5’ 11”) tall man tosses a ball from his height position (e.g. ball leaves his hand at level of the top of his head) to a hard board 2m high and 3.0 m distant. If the ball strikes the board at a height of 1.5 m, find: a) the initial speed of the ball; (b) the time of flight, and c) the speed when it hits the board. (Assume g = 10 m/s2)
2. A rocket is fired at a launch angle of 30 degrees, and at an initial velocity of u = 500 m/s. Find: a) the horizontal range, b) the greatest altitude (h) reached, and c) the time taken to reach h. (Assume g = 10 m/s2)
3. Find the acceleration with which a 2 kg mass accelerates down a frictionless inclined plane (angle of incline = 30 degrees) (Assume g = 10 m/s2)
All the preceding problems are fairly basic, none requires anything more than algebra- level math to solve, yet one finds fewer than 1 in 5 pre-med or biology majors can do them. Why? The reason in most cases is that they immediately attempt to recall the "formula" that will be exactly right to solve it, without being aware of the context.
The context only becomes apparent when the student lays out the specific problem, i.e. in a working diagram. At the top of the page I show how one of the few successful pre-med students presented each of the three problems, using appropriate diagrams. It then becomes clear (certainly to the physics prof) that the ability to sketch a problem diagram is part and parcel of successful problem solving. You can't just do an instant recall of one of some four hundred memorized formulae and expect success.
But doing the correct diagram paves the way to seeing manner of solution. Consider problem (3) for example. Given the diagram above we can proceed:
We find the component of acceleration of the 2 kg mass along the incline is mg sin q
This is also the component needed to apply Newton's 2nd law of motion: F = ma
(Force = mass times acceleration), so:
F = ma = mg sin q
q = 30 degrees
so the acceleration: a = g sin q = (10 m/s2) sin (30) = 10 m/s2(1/2)
or a = 2 m/s2
The other two problems are somewhat more involved, but follow on in a similar manner from the correct use of the diagrams.
My point is that the successful physics student needs to ditch the reliance on memorizing formulas, equations and understand first the layout of the particular problem. What is being asked, and how can one physically represent this?
The other comment by the same prof is also illuminating:
"The second problem is an aggressive and obsessive quest for an A. I think the pathological anxiety about grades stands in the way of learning a difficult subject like physics. Though pre-med students regularly perceive anything less than a 4.0 spells doom, mediocre students with less than average GPA routinely get into med schools."
This is also quite true, but this "A-obsession" isn't merely confined to the pre-med lot, it infects virtually every discipline. It is also part of the reason that grade inflation has infected every facet of academia, including physics! Only the strongest, most fearless physics profs are prepared to avoid this infection and - as I have - tell students they will get exactly what they earn, not some inflated version of it. (Of course, one must be prepared to face the evaluation fallout!) But if this isn't done, and the prof or lecturer gives in out of extortion, then the subject itself becomes contaminated and diluted.
The other part of this issue is that when one yields to grade inflation and "A obsession" one automatically sets the stage for the extension and reinforcement of the very memorization methods that are inimical to students really learning physics. The reason is that mediocre marks, grades are more likely to flow (at least initially) when the proper methods for problem solution are used, though the students will get better with greater exposure. But in a difficult subject with difficult problems one simply can't expect a 95% on every exam!
Another letter writer posed the following:
"Physics professors have to constantly remind themselves that mathematics is a foreign language to most biology students. They are language oriented and can learn the names of countless chemicals and medicines that most physicists would never attempt to master."
This is true, but if the situation were reversed, and Biology was required of all physics students, and they had to master all the species names in assorted Phyla, etc. to pass the course, you can bet your sweet bippy they would, i.e. memorize what they had to. Similarly, if they had to memorize a mass of data, drug names, medical conditions in a pre-med course, they would. In the same way, a pre-med or biology student needs to grasp that he or she is expected to fulfill a certain level of aptitude in problem solving, say to excel in (or even pass) a physics course. You can't expect the physics prof or department to dilute the courses of all mathematics because the biology, pre-med students treat math as a "foreign language".
Again, we're not talking about differential calculus to solve problems in the first year physics courses that life science majors take. We're talking basic algebra! My belief, and it's strong, is that if a college student can't even pose problems in terms of algebra - or use algebra - he or she has no business being in college in the first place. (One is forced to ask how they even made it through the Math section of the SAT.)
Finally, one prof from the University of Wisconsin might have proposed the most pragmatic solution, when he wrote:
"Biologists have worked in a much more qualitative context than physicists. But with the advent of modern simulation, the intractability of analytic understanding is becoming less of a problem, and biology might be expected to become much more akin to computational physics. Therefore, we might think of educating biologists more in computational than analytical physics."
Fortunately, a good computational physics course shouldn't be too difficult to draw up. However, one proviso I would have is that it still needs to contain the core analytical sections as they relate to the most fundamental principles of physics, i.e. Newton's laws of motion, the laws of thermodynamics.