“Physics with a Smile” – Explaining Phenomena with a Qualitative Problem-Solving Strategy, Roni Mualem and Bat-Sheva Eylon

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 fosteringqualitative 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 ofNewton’s laws, especially the third law. The approach also aimsto change students’ interest in physics and their views regardingits importance. It was tried out extensively with heterogeneous ninth-gradersand has also been integrated into the teaching of mechanicsat the advanced high school level.

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 Newton’s second law, dealing mainly with situations in which objects start or stop their motion. We found that although the previously described framework helped students to construct qualitative explanations, many students were still unable to formulate such explanations. We hypothesized that in addition to the conceptual framework, students need a qualitative problem-solving strategy that would guide them through the problem-solving process.11,12,13

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 stepsthat promote a clear subdivision of the problem-solving process thatare presented separately on colored index cards. One side ofthe card includes instructions for carrying out the relevant partof the strategy, and the other side includes guiding questionsthat are designed to assist the students to follow theinstructions accurately. Visual representations are used in the strategy asexemplified 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 ofthe system.

1.b. Constructing a table including all the interactions betweenobjects 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).

  1. 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 pairsof forces in the block diagram using the table ofinteractions.

2.b. Selecting an object and “gathering” all the forces thatact on it using the block diagram.

The guiding questions emphasizeNewton’s third law (N3) and ensure that all the forcesthat act on the object appear in the free-body diagramof the step stage. The relative magnitudes of the forcesthat act on the object are not considered. Note thatinteractions at a distance are marked by a dotted line.

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).

  1. The third step (“forces and motion”)allows the students to analyze the situation by constructing acomplete free-body diagram and relating it to the motion characteristics.The relative length of the arrows that represent these forcesin the diagram can be determined based on information givenin the problem or can be deduced from the characteristicsof the object’s motion. This step enables the students tolink between forces and motion by delineating the relations betweenthe forces and the observed motion (Newton’s second law—N2).

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 analyzingcomplex situations, as well as ill-defined problems that characterize authenticsituations 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 tothe conceptual level that they have reached until they areable to perform the complete analysis and to employ allthe 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 Newton’s third law (N3) from the Force Concept Inventory.16 These items are considered to be difficult because of their counterintuitive nature. Table I shows the results on these items.

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 airis released from the balloon?

Student: Because there is an interactionthe air exerts a force on the balloon this way(points to the correct direction).

Interviewer: What will happen to therocket balloon?

Student: It will move this way (correct), if thepushing force is greater than the friction force.

Interviewer: Let’s takesomething else Suppose you release the balloon but it doesn’tmove?

Student: The friction force can exert a force up toa certain magnitude and when you have a larger magnitudethe object will move but here this didn’t happen sothe 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 formallanguage and handles friction very well. He is also showinga more expert-like performance and mastery of understanding performances thatwere 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 theninth-grade students scored better in this N3 matriculation itemthan 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 tothe students after instruction, show that students believed that thestrategy used in this method helped them in analyzing situationsand that they would like to study other disciplines inthe same manner as they had studied physics.

The teaching method was introduced to junior high school science teachers (n=150) throughinservice training courses entitled “Who’s Afraid of Physics?” Teachers reportthat they gained self-confidence in their ability to explain everydayphenomena, changed their views about the relevance and interest ofphysics to the students, and were willing to implement themethod in their classes.


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 interactionconcept.
  2. The qualitative approach that does not employ any mathematicaltools, yet leads to a traditional physical description (like aforce diagram).
  3. The characteristics of the strategy and the procedures:
  • Visual representations: block diagrams, interaction tables, force diagrams.
  • Thedivision of the problem-solving process into simple steps.
  1. The tasksdealing with authentic situations that are familiar and relevant tothe students.
  2. The “physics with a smile” approach that employs practice cards with user-friendly drawings (see Figs. 12) and makesthe subject of physics less threatening.

This approach is already beingadopted in many ninth-grade classrooms in Israel. Modest beginnings showthat teaching with this method in the ninth grade increasesthe number of students who choose physics in senior highschool and improves their standard problem-solving skills. Introducing the qualitativeapproach in the ninth grade can function as a foundationand basis for the quantitative treatment in later years. Theapproach can also be integrated into the teaching of physicsin senior high school before introducing quantitative problem solving.


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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 Israel. Roni specializes in JHS teaching of physics and astronomy.

Bat-Sheva Eylon is an associate professor in the department of science teaching at the Weizmann Institute of Science, Israel. Her work focuses on the development and study of cognitive tools for enhancing conceptual understanding, problem solving, and knowledge integration in high school physics.Department of Science Teaching, The Weizmann Institute of Science, Rehovot, Israel, 76100; Roni.Mualem@weizmann.ac.il; b.eylon@weizmann.ac.il


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)

First citation in article

Table II. Students’ achievements in a problem taken from the physics matriculation exam. The ninth-graders studied by the method described herein.
Group n answered correctly (%) explained correctly (%)
Heterogeneous ninth-graders 360 47 41
Advanced physics 12th-graders 1115 42 31