Reprinted with
permission from: The Physics Teacher, Vol. 45, No. 3, pp. 158–163, March 2007
©2007 American Association of Physics Teachers.
“Physics with a Smile”—Explaining Phenomena with a
Qualitative Problem-Solving Strategy
Roni Mualem and Bat-Sheva Eylon
The Weizmann
Institute of Science ,
Rehovot ,
Israel
Various studies indicate that high school physics students
and even college students majoring in physics have difficulties in
qualitative understanding of basic concepts and principles of physics.1,2,3,4,5
For example, studies carried out with the Force Concept Inventory (FCI)1,6
illustrate that qualitative tasks are not easy to solve even at the
college level. Consequently, “conceptual physics” courses have been
designed to foster qualitative understanding, and advanced high school physics
courses as well as introductory college-level courses strive to develop
qualitative understanding. Many physics education researchers emphasize the
importance of acquiring some qualitative understanding of basic
concepts in physics as early as middle school or in the context of
courses that offer “Physics First” in the ninth grade before biology
or chemistry.7
This trend is consistent with the call to focus the science
curriculum on a small number of basic concepts and ideas, and to
instruct students in a more “meaningful way” leading to better
understanding. Studies7,8,9,10
suggest that familiar everyday contexts (see Fig. 1)
are useful in fostering qualitative
understanding.
Fig. 1. An example of a qualitative task describing a situation—a man pulls a dog but the dog does not move. The students are asked to explain the situation by using basic concepts and ideas of physics.
Developing Qualitative
Understanding
We
describe a new teaching approach in mechanics for junior high school
(JHS) and high school (as an introduction) that requires around
15–30 teaching hours. The approach guides students to explain and
predict qualitatively, using physical terms, a class of everyday
phenomena and situations in mechanics (see Fig. 2)
by applying a qualitative understanding of
Fig. 2. Situations with interacting objects.
This
method takes a systems approach and does not detach the object from
its surroundings. It encourages students to analyze the interactions
among components of the entire system before focusing on a specific
object and constructing its free-body diagram. Students learn to
systematically identify short and longterm
interactions and to characterize the mutual influences on shape
and/or speed of interacting objects. A qualitative study of basic
motion concepts is followed by a qualitative study of
The
Problem-Solving Strategy and an Example
The
qualitative strategy is inspired by Reif's work
on physics problem solving.13 It consists of
three steps that promote a clear subdivision of the problem-solving
process that are presented separately on colored
index cards. One side of the card includes instructions for carrying
out the relevant part of the strategy, and the other side includes
guiding questions that are designed to assist the students to follow
the instructions accurately. Visual representations are used in the
strategy as exemplified below.
1. The first step (“system characterization”)
consists of two substeps that enable the
student to consider the subsystems and all the interactions before
focusing on a certain object.
1.a. Representing
the situation by a block diagram involving components of the system.
1.b.
Constructing a table including all the interactions between objects
within the system.
The accompanying guiding questions to this step assure that the students do not omit any long-range and/or short-range interactions.11
For
example, consider the situation presented in Fig. 1. In this step, the student
translates the situation, first to a block diagram [Fig. 3(a)] and then to a table of
interactions [Fig. 3(b)].
Fig. 3a. A block diagram (step 1.a). Fig. 3b. Table of interactions (1.b).
2. The second step (“from systems to selected
objects”) is designed to lead the student to draw a
free-body diagram of a selected object. The process is performed in
two stages:
2.a.
Marking all the pairs of forces in the block diagram using the table
of interactions.
2.b.
Selecting an object and “gathering” all the forces that act on it
using the block diagram.
The
guiding questions emphasize
If
we apply the second step in our example (see Fig. 1) we
get Fig. 4(a). Isolating the selected object,
in this case the dog, and marking the objects that exert forces
on it without considering the magnitude of the forces leads to Fig. 4(b).
Fig. 4a. Marking forces in the block diagram (2.a). Fig. 4b. Isolating a selected object (2.b).
3. The third step (“forces and motion”) allows
the students to analyze the situation by constructing a complete
free-body diagram and relating it to the motion characteristics. The
relative length of the arrows that represent these forces in the
diagram can be determined based on information given in the problem
or can be deduced from the characteristics of the object's motion.
This step enables the students to link between forces and motion by
delineating the relations between the forces and the observed motion
(
This
step allows the student to (a) deduce forces from motion information
as described above; (b) deduce motion characteristics from a force diagram;
and (c) based on Newton's laws, predict what will happen in a situation,
observe the outcome, and explain it (POE12— Predict, Observe,
and Explain).
In
our example, the dog does not move (motion characteristics are
known). Thus, the net force along each axis should equal zero. That
means that the arrows along each axis have equal length and are in
opposite directions (Fig. 5).
Fig. 5. A complete force diagram.
This
approach is especially useful in analyzing complex situations, as
well as ill-defined problems that characterize authentic situations
familiar to students.
The
Teaching Process
The
teaching sequence consists of presenting the conceptual framework
and the qualitative strategy in a combined manner. During the
teaching process several selected situations, illustrated as comic
drawings (see Fig. 2),
are analyzed several times. Each time the students carry out an
analysis corresponding to the conceptual level that they have
reached until they are able to perform the complete analysis and to
employ all the concepts learned in the program (a spiral analysis).
Evaluating
the Effectiveness of the Approach
A
study was conducted with ninth-grade students (n=242) who
studied according to this approach. Pre- and post-questionnaires, administered
to the students, included a few items that deal with
As
indicated in the table the average <g> of these students
is high as compared with achievements of college-level students studying
by traditional methods (for example, a value of <g>=0.28 was
reported by Redish17
et al.). These students demonstrated in interviews an improved
ability to explain and predict phenomena using physics ideas. In
pre-interviews conducted with some of these students (n=69),
they used only intuitive reasoning and colloquial language in explaining
and predicting phenomena, while in the post interviews they showed a
more expert-like performance13,14
using physical terms, physics principles, and force diagrams. The
following excerpt illustrates the nature of explanations given by
students after instruction (see Fig. 6):
Interviewer: What
will happen to the rocket balloon when the air is released from the
balloon?
Student:
Because there is an interaction
the air exerts a force on the balloon this way (points to the
correct direction).
Interviewer: What
will happen to the rocket balloon?
Student: It
will move this way (correct), if the pushing force is greater than
the friction force.
Interviewer: Let's
take something else
Suppose you release the balloon but it doesn't move?
Student: The
friction force can exert a force up to a certain magnitude and when
you have a larger magnitude the object will move
but here this didn't happen
so the balloon didn't move.
Fig. 6. “A Rocket Balloon”—a balloon on a fishing line. A small balloon that is filled with air is hooked to a fishing line and is allowed to move along the line when the air is released. The student needs to explain why the balloon is moving if it is fully filled with air but does not move when only partly filled.
In
this sample, the student uses formal language and handles friction
very well. He is also showing a more expert-like performance and
mastery of understanding performances that were on focus (prediction
and explaining).
A selected item from the Israeli matriculation
examination in physics that dealt with N3 (see Fig. 7)
was added to the post-questionnaire. Results on this
matriculation question are shown in Table II
showing that the ninth-grade students scored better in this N3
matriculation item than high school students majoring in physics.
Fig. 7. The Israeli matriculation question. The student's claim is incorrect because the box is involved with two interactions: one is with the Earth and the other is with the rope.
Attitude
questionnaires, administered to the students after instruction, show
that students believed that the strategy used in this method helped
them in analyzing situations and that they would like to study other
disciplines in the same manner as they had studied physics.
The
teaching method was introduced to junior high school science
teachers (n=150) through inservice
training courses entitled “Who's Afraid of Physics?” Teachers report that they gained self-confidence in their ability
to explain everyday phenomena, changed their views about the
relevance and interest of physics to the students, and were
willing to implement the method in their classes.
Summary
Traditionally,
problem-solving strategies in high school are used for solving
quantitative problems and not for tasks requiring the construction
of explanations or for predictions. Qualitative problems such as the
ones in the FCI are considered as “one-step” problems that do not
require the use of a strategy. The present paper suggests that this
assumption is unjustified and that a combination of a useful
conceptual framework with a qualitative problem-solving strategy can
bring ninth-grade students to impressive achievements in explaining
and predicting phenomena in comparison to achievements of senior
high school students in advanced physics courses. In addition, this
empowerment of students and teachers led to a positive change in
attitudes and confidence. We suggest that the success of this method
stems from several factors:
1.
The conceptual framework that emphasizes the “system's
approach” and uses the interaction concept.
2.
The qualitative approach that does not employ any mathematical tools,
yet leads to a traditional physical description (like a force
diagram).
3.
The characteristics of the strategy and the procedures:
•
Visual representations: block diagrams, interaction tables, force diagrams.
•
The division of the problem-solving process into simple steps.
4.
The tasks dealing with authentic situations that are familiar
and relevant to the students.
5.
The “physics with a smile” approach that employs practice
cards with user-friendly drawings (see Figs. 1-2) and makes the
subject of physics less threatening.
This
approach is already being adopted in many ninth-grade classrooms in
REFERENCES
- Richard R. Hake, “Interactive-engagement versus traditional methods: A six-thousand-student survey of mechanics test data for introductory physics courses,” Am. J. Phys. 66, 64–74 (Jan. 1998).
- Jim Minstrell, “Getting the facts straight,” Sci. Teach. 50, 52–54 (Jan. 1983).
- Edward F. Redish, “Diagnosing students' problems using the results and method of physics education research,” Paper presented at the International Conference on Physics Teaching, Guilin, China (Aug. 1999).
- Ibrahim Halloun and David Hestenes, “The initial knowledge state of college physics students,” Am. J. Phys. 53, 1043–1055 (Nov. 1985).
- Lillian C. McDermott, “Research on conceptual understanding in mechanics,” Phys. Today 37, 24–32 (July 1984).
- Richard N. Steinberg and Mel S. Sabella, “Performance on multi-choice diagnostics and complementary exam problems,” Phys. Teach. 35, 150–155 (March 1997).
- Physics First site, http://members.aol.com/physicsfirst.
- Project 2061 site, http://www.project2061.org/default.htm.
- Kevin Pugh, “
- Luli Stern and Andrew Ahlgren, “Analysis of students' assessment in JHS curriculum materials: Aiming precisely at benchmarks and standards,” J. Res. Sci. Teach. 39, 889–910 (May 2002).
- Lou Turner, “System schemas,” Phys. Teach. 41, 404–408 (Oct. 2003).
- White and Gunstone, Probing Understanding (The Falmer Press, New York, NY, 1992).
- Frederick Reif, “Millikan Lecture 1994: Understanding and teaching important scientific thought processes,” Am. J. Phys. 63, 17–32 (Jan 1995).
- B. White and J. Frederiksen, “Causal model progressions as a foundation for intelligent learning environments,” Artificial Intelligence 24, 99–157 (1990).
- M. T. H. Chi, M. Bassok, M. W. Lewis, P. Reimann, and R. Glaser, “Self-explanations: How students study and use examples in learning to solve problems,” Cogn. Sci. 13, 145–182 (1989). [Inspec]
- David Hestenes, Malcom Wells, and Greg Swackhamer, “Force Concept Inventory,” Phys. Teach. 30, 141–158 (March 1992).
- Edward F. Redish, Jeffery M. Saul, and Richard N. Steinberg, “On the effectiveness of active-engagement microcomputer-based laboratory,” Am. J. Phys. 65, 45–54 (Jan. 1997).
About
the Authors
Roni Mualem has
been teaching physics for 15 years in middle schools, high schools,
and in college. He is also a Ph.D. student in the science teaching
department of the Weizmann Institute of
Science in
Bat-Sheva Eylon is an
associate professor in the department of science teaching at the Weizmann Institute of Science,
TABLES
|
Table I. The FCI sub-test: the degree of progress of JHS students who ere taught with our method. |
|||
|
FCI item (from N3) |
No. of classes |
No. of students |
<g>** |
|
2 |
11 |
242 |
0.68 |
|
11 |
11 |
242 |
0.46 |
|
13 |
11 |
242 |
0.58 |
|
14* |
3 |
61 |
0.82 |
|
average |
|
|
0.64 |
|
* The question was administered only in three of the seven classes that participated in the study |
|
|
|
|
** <g> is the degree of progress1 of the students and indicates the real effectiveness of the approach. <g> = (post-test score − pre-test score)/(100 − pre-test score) |
|||