| Arnold Arons' Guide to Introductory Physics Teaching
eloquently testifies, in subsections bearing such titles as "misleading
terminology" and "what we say can hurt," to the need for instructors to
use clear, consistent language.1,2 Indeed we all attest that
words matter every time we make careful distinctions between words such
as "speed" and "velocity." Unfortunately, our vocabulary often does
little to guide students toward proper concepts and occasionally even
contradicts the desired concepts, making learning more difficult and
misconceptions more likely. Most ripe for change is the word "heat." As we all know, heat is a process, a form of energy transfer,
and not a form of energy. But our usage belies this meaning. Since it
is a process, we should treat "heat" as a verb, but instead we treat it
as a noun. Following Arons' precept "idea first and name afterwards,"3
we should begin with simple examples such as heating a pot of soup on
the stove. Then a formal definition: Any spontaneous transfer of
thermal energy (students should already understand thermal energy, i.e.
internal energy) from a hot to a cold body because of a temperature
difference is called "heating." We say that the flame "heats" the pot.
This must be followed up with a consistent use of "heat" only as an
action-"to heat" or "heating"-not a thing. If the instructor says for
example "heat is transferred to the pot," students will conclude that
heat is an entity that can be transferred the way that energy can be
transferred. We should speak of "thermal energy flow" (or "thermal
energy transfer"), never "heat flow" (or "heat transfer"). There's an
important difference between thermal energy (a form of energy) and
heating (one form of thermal energy transfer). "Heat"
exemplifies physicists' unfortunate tendency to turn actions into
things, i.e. to make nouns out of verbs. Another example is "work." As
with heat, students often misconceive work to be a substance, similar
to energy. But again work is a process, a way of transferring energy,
not a form of energy. A body does work, and it does heating, but it has
energy. The rule is that "to do work" and "to heat" are verbs, while
"energy" is a noun. Logically, we should say "A works on B," a parallel
construction to "A heats B." However the accepted form "A does work on
B" is not bad, so long as we never let it degenerate into "A adds work
(or provides work) to B." There
is a similar problem with "force." "Force" is an action, similar to
work and heating, but physicists have turned it entirely into a noun,
as in "A exerts a force on B." But force is an action, e.g. a push or a
pull, and should be treated linguistically just like "push." We would
normally say "A pushes B" rather than "A exerts a push on B."
Unfortunately, the equivalent construction "A forces B" is never used.
If we did use this construction (and I'm not necessarily advocating
it), it would reduce misconceptions. "A exerts a force on B" reinforces
the misconception that there is some entity, "a force," that A
bequeaths to B and that B then carries with it. It would help if we
instead used the terms "interact" and "interaction strength" whenever
possible, as in "A interacts with B" or better yet "A and B interact."
Since "interact" is clearly an action, this usage might resolve some
conceptual problems while also more naturally suggesting Newton's third
law. Do we
really need the term "centripetal force"? When we name it, students
naturally conclude, wrongly, that this is a new kind of force. How many
times have students told us, for example, that the forces acting on a
satellite are gravity and the centripetal force? "Net force" and "acceleration" should be all that are needed to discuss circular motion. It
would be more descriptive, less boring, and historically more accurate,
to replace the titles of Newton's first, second and third laws with the
law of inertia (Descartes and Galileo, not Newton, first formulated
it), Newton's law of motion, and the law of force pairs (or the law of
interactions). "Potential"
is overused and confusing. There are at least five common forms of
potential energy: gravitational, elastic, electromagnetic, chemical
(microscopic electromagnetic energy), and nuclear. But the adjective
"potential" is usually applied only to the first three of these. To
further confuse matters, there is an "electric potential" in
electromagnetism, but it is not a form of energy; instead it is an
electric energy per unit charge. Furthermore, students think of
potential energy as only potential, as opposed to actual; this is a
misconception, because the potential forms of energy are fully as "actual" or "real" as the kinetic forms.
Why not drop the term "potential" in connection with energy, and
instead use the more descriptive terms gravitational energy, elastic
energy, etc.? Turning
to modern physics, "quantum mechanics" gives students the enormous
misconception that this is a mechanistic theory, similar to Newton's
mechanics. But the quantum world is not like a machine. It is not made
of Newton's "solid, massey, hard, impenetrable particles" that "never
wear or break in pieces."4 It is non-deterministic, and it
is deeply entangled and non-local rather than made of localized parts.
"Quantum physics" would be a better term. It
can be misleading to speak of quantum "uncertainties," because it puts
students in mind of a quantity having a definite value that is however
unknown to the observer, a view of quantum physics that is demonstrably
incorrect.5 Heisenberg used the German "Unbestimmtheit"
(usually translated as "indeterminacy" although it can also mean
"uncertainty") rather than "Unsicherheit" (uncertainty).6
The English "indeterminacy" seems to better capture the correct quantum
concept that precise positions, momenta, etc. do not, in general,
exist, i.e. there is no precise position or momentum for an object such
as an electron.2,7 We
should include exciting new topics such as string theory in our
introductory courses. But we should be careful with the word "theory."
"String theory" is a misleading term, since it is not yet an
empirically tested theory but is instead a wonderful and well-developed
hypothesis. The distinction between a plausible supposition or
"hypothesis," and a well-tested body of ideas or "theory," is crucial
in science education, especially when discussing scientific methodology
and pseudosciences such as creationism and astrology. We should speak
of the "string hypothesis."8 Wouldn't
it be nice if the physics education community could come to a meeting
of minds on improved usage for some of these terms, and recommend new
standard usages that most textbooks, articles and teachers would then
use consistently? References - Arnold Arons, A Guide to Introductory Physics Teaching (John Wiley & Sons, New York, 1990)
- See also M. Thomas Williams, "Semantics in teaching introductory physics," Am. J. Phys. 67, 670-680 (1999).
- Ref. 1, p. 23; italics in the original.
- Alan L. Mackay, A Dictionary of Scientific Quotations (Adam Hilger, New York, 1991), p. 181.
- Daniel F. Styer, "Common misconceptions concerning quantum mechanics," Am. J. Phys. 64, 31-34 (1996).
- Werner Heisenberg, "Die Rolle der Unbestimmtheitsrelationen in der modernen Physik," Monatshefte für Mathematik und Physik (Leipzig) 38, 365-372 (1931).
- Andrew Whitaker, Einstein, Bohr and the Quantum Dilemma
(Cambridge, New York, 1996), makes the point (pp. 147-8) that we should
speak of quantum indeterminacy rather than uncertainty.
- However, I must admit that I have gone along with the crowd and called it "string theory" in my textbook Physics: Concepts and Connections (Prentice Hall, Upper Saddle River, NJ, 3rd edition 2003).
Art
Hobson, Professor Emeritus of Physics at the University of Arkansas,
Fayetteville, is the author of the liberal-arts physics textbook:
Physics: Concepts and Connections as well as The Future of
Land-Based Strategic Missiles, (American Institute of Physics, 1989),
Physics and Human Affairs, (John Wiley, NY, 1982) and Concepts in
Statistical Mechanics, (Gordon and Breach, NY, 1971). Email: ahobson@uark.edu |