Summary: McDermott, et al.end of the bat. They were told that the bat was of uniform
mass density and asked to compare the total mass to the left
and right of the balance point. Only about 15% of the K-5
teachers responded correctly. Nearly everyone who gave an
incorrect answer claimed there must be equal mass on both
sides. They did not seem to be aware that it is not only the
amount of mass but also its distribution that determines the
turning effect.
A question to probe understanding of acceleration was
administered to about 180 preservice and inservice teachers
(primarily grades 9–12). The question was based on a strobe
diagram of a ball rolling up and down an inclined ramp. Only
about 50% of the teachers drew correct sketches that showed
acceleration vectors of constant magnitude that were always
directed down the ramp. The most common incorrect answers
were that the acceleration would be zero at the turnaround
point or directed vertically downward, rather than always
along the ramp.
The topic of electric circuits is included in many precol-
lege curricula. We have frequently asked for the ranking of
the brightness of identical bulbs in three circuits with iden-
tical, ideal batteries. The circuits contain, respectively, one
bulb, two bulbs in series, and two bulbs in parallel. The cor-
rect ranking is that the single bulb and the two in parallel are
equally bright and brighter than the two in series. Of the many
teachers who have been asked this question, only about 15%
have given a correct ranking. Research has revealed two wide-
spread mistaken beliefs: (1) the battery is a constant current
source and (2) current is “used up” in a circuit.
Our development of an instructional sequence in the
Dynamics module in Physics by Inquiry was motivated by the
inability of many students to apply Newton’s Laws properly.
In one example, students were shown a diagram of a sys-
tem consisting of three blocks in horizontal contact with one
another. A hand pushes horizontally on one of the end blocks,
thus accelerating the system. The question asked was how, if
at all, the acceleration changes if the middle block is replaced
by one of greater mass while the hand exerts the same horizon-
tal force. To answer that the acceleration has decreased, stu-
dents must recognize that the inertial mass has increased while
the net force exerted on the blocks has remained the same.
When this question was administered after standard instruc-
tion in introductory physics, fewer than 20% of the students
answered correctly. The question has also been given to intro-
ductory physics students (N > 100) after they have worked
through the tutorial on Newton’s Second and Third Laws in
Tutorials in Introductory Physics, our supplementary curricu-
lum in which the treatment of Newton’s Laws is less thorough
than in Physics by Inquiry.^7 About 55% (N ~ 720) gave correct
responses. While this improvement (i.e., 20% to 55%) is sig-
nifi cant, high school teachers must understand the material at adeeper level than students in an introductory university course.
About 90% of the teachers (N = 45) who worked through the
Dynamics module in PbI gave a correct response.
The research paper also contains an example from geometri-
cal optics that demonstrates the positive effect that even inex-
perienced teachers can have when they understand the material
in depth. Their study of this topic begins with a pretest on the
image produced by a triangular hole in a mask placed between
a long-fi lament bulb and a screen. Like introductory physics
students, only about 20% of our teachers have responded cor-
rectly. Most have had no mental model in which light rays travel
in straight lines in all directions from every point on an object.
After working through the Light and Color module in PbI, the
teachers develop a ray model that enables them to account for
the patterns formed by light sources and apertures of various
shapes. After teaching this topic in a ninth-grade classroom,
the preservice teachers have given a post-test. About 45% of
their students have given correct answers. If the teachers had
not developed a ray model, their students would likely have
done no better than they had done on the pretest.
When research in physics education has a strong discipli-
nary focus, it can signifi cantly contribute to the preparation
and professional development of precollege teachers. The
research summarized in this article should help convince
university faculty about the type of preparation in phys-
ics that teachers need. The article also contains data from
other populations, which are a resource that instructors can
draw upon in teaching students at the introductory level and
beyond.(^1) The 2006 article accompanied an editorial that described in detail some gen-
eral issues relevant to physics teacher preparation that are described in this
summary. See, Lillian C. McDermott, “Editorial: Preparing K-12 teachers in
physics: Insights from history, experience, and research,” Am. J. Phys. 74 ,
758-762 (2006).
(^2) At the elementary school level, the curricula included Elementary Science
Study (ESS), Science Curriculum Improvement Study (SCIS), and Science – A
Process Approach (SAPA).
(^3) A. Arons wrote The Various Language (Oxford University Press, NY, 1977)
while teaching this course.
(^4) L.C. McDermott and the Physics Education Group at the University
of Washington, Physics by Inquiry (John Wiley & Sons, NY, 1996).
Development of the published curriculum began in the combined course.
(^5) These were initially inspired by the clinical interviews of J. Piaget, a Swiss
psychologist.
(^6) D.E. Trowbridge and L.C. McDermott, “Investigation of student under-
standing of the concept of velocity in one dimension,” Am. J. Phys. 48 (12)
1020-1028 (1980); D.E. Trowbridge and L.C. McDermott, “Investigation of
student understanding of the concept of acceleration in one dimension,” ibid.
49 (3) 242-253 (1981). These articles were the fi rst in AJP resulting from
research toward a physics Ph.D. in a U.S. physics department.
(^7) L.C. McDermott, P.S. Shaffer and the Physics Education Group at the
University of Washington, Tutorials in Introductory Physics, First Edition
(Prentice Hall, Upper Sadddle River, NJ, 2002); Instructor’s Guide, 2003. A
Preliminary Edition was published in 1998.
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