Discrepant Events: A Challenge to Students' Intuition

Discrepant Events: A Challenge to Students' Intuition Cite as: The Physics Teacher 48, 508 (2010); https://doi.org/10.1119/1.3502499 Published Online: 22 October 2010 Wilson J. González-Espada, Jennifer Birriel, and Ignacio Birriel ARTICLES YOU MAY BE INTERESTED IN Keep Them Guessing The Physics Teacher 51, 438 (2013); https://doi.org/10.1119/1.4820864 The First Three Minutes … of Class The Physics Teacher 44, 477 (2006); https://doi.org/10.1119/1.2353601 Gravity, Time, and Lagrangians The Physics Teacher 48, 512 (2010); https://doi.org/10.1119/1.3502500 The Physics Teacher 48, 508 (2010); https://doi.org/10.1119/1.3502499 © 2010 American Association of Physics Teachers. 48, 508 Discrepant Events: A Challenge to Students’ Intuition Wilson J. González-Espada, Jennifer Birriel, and Ignacio Birriel, Morehead State University, Morehead, KY S tudies on cognitive aspects of science education, especially how students achieve conceptual change, have been a focus of interest for many years.1 Researchers of student learning and conceptual change have developed several easily applicable teaching strategies. One of these strategies is known as discrepant events. Discrepant events are very powerful ways to stimulate interest, motivate students to challenge their covert science misconceptions, and promote higher-order thinking skills. The key point is that directly challenging students’ naive ideas will lead to more quality science learning going on in the classroom. In this paper, we summarize the research-based role of discrepant events in conceptual change and we share several highly successful discrepant events we use in our own classes. Learning is a constructive process in which an active learner builds his or her own knowledge from his or her collective experiences.2 Sometimes, however, the information is inaccurate to begin with, or is not remembered properly, or is integrated into the cognitive scaffolding in unexpected ways. The result is that students will sometimes have ideas that are inconsistent with scientifically accepted notions of how the natural world works. These notions are commonly called preconceptions, naive conceptions, naive theories, alternative frameworks, or misconceptions.3,4 One way to challenge students’ naive ideas is to apply the conceptual change model of science learning. This model proposes making students aware of the inadequacies of their own explanations by exposing them to evidence that directly contradicts their ideas, therefore creating cognitive conflict.5 This should result in students’ becoming intrinsically motivated to create alternate explanations and to find out why their ideas are inconsistent with their observations. Overall, positive pedagogical effects of creating and resolving cognitive conflict have been documented in the literature.6 A simple way to create cognitive conflict, or cognitive dissonance, is through the use of discrepant events.7,8 A discrepant event is defined as a situation whose outcome is inconsistent with what one would expect. Discrepant events promote student motivation and effectively facilitate cognitive gains in students.5 Mason et al.9 summarize the main advantages of using discrepant events for teaching science: “Discrepant events evoke dissatisfaction with one’s content knowledge and in certain cases cause teachers to reconsider their pedagogical practices. Discrepant events may also aid students in resolving conflicts between their naïve conceptions and the accepted sci- 508 entific explanation and, in addition, serve to fascinate, engage, arouse curiosity, motivate, and stimulate intellectual development in learning scientific concepts.” (p. 1309). The idea is, as Tim Slater ingeniously said, to offend your students’ intuition.10 Discrepant events have been successfully used in biology, chemistry, physics, and even social studies and teacher training.11,12 In one version of the strategy, the teacher asks students to predict what they expect to happen and why they think it should happen that way before the teacher presents the demonstration. Then students observe what happens and are asked to modify their previous explanation.13 In another version, the teacher acts as if the demonstration will turn out as expected, and he or she is “surprised” when the result is unexpected. The teacher acts like a magician who sets up students into expecting something, and students are caught off guard by what actually happens. Below, we share a sampler of discrepant events that our students have considered most surprising or informative. Nature of science switcheroo Among the basic tenets of science is that most events in the universe occur in consistent patterns that are comprehensible and that the same basic science rules are applicable everywhere. As a consequence, science can explain and predict phenomena. One way to demonstrate this fact is by quantifying the relationship between the release height of a bouncy ball and its bouncing height. A bouncy ball is placed 35 cm from the floor and released, then grabbed at its highest rebounding point. The data are plotted on a graph of bouncing height (y-axis) as a function of release height (x-axis). This process is repeated with the bouncy ball dropped from a height of 70 cm and the rebounding height recorded. The third time the bouncy ball is released from a height of 100 cm, but this time the ball “accidentally” hits the instructor’s shoe and rolls on the floor. The instructor, appearing embarrassed, places the ball in his or her front pocket and returns to the board to ask students to predict, based on the data, what should be the next rebounding height. After students have predicted possible values, the instructor gets the ball from the pocket and releases it from the 100-cm mark. The ball is dropped and students are taken aback when the ball fails to bounce at all! When asked what happened, many students will question whether the ball grabbed from the pocket is the same one used before, precisely because they are beginning to under- THE PHYSICS TEACHER ◆ Vol. 48, NOVEMBER 2010 DOI: 10.1119/1.3502499 stand that most things and events in the universe occur in consistent patterns that are comprehensible. A completely different behavior for an object is contrary to this premise. Of course the “trick” is that the instructor is using identical happy/sad balls. Radioactive or not? We teach students that science is the study of patterns in nature. In reality, however, pattern recognition in nature is far from simple.14,15 One interesting demonstration of this is the determination of which materials are radioactive and which are not. the other color marbles are “cold,” the antique jewelry is “hot,” and the Atomic Fireballs are not “hot.” Each teacher can find her or his own set of “hot” and “cold” items but must develop some sort of pattern. This demonstration works best with a fair amount of showmanship. For example, students can be guided into thinking “green” and “glass” equates with “hot.” In addition, with the salt being “hot” and the Atomic Fireball burning your mouth, one can really convince students that this favorite candy might actually be radioactive! The main point of this demonstration, however, is that pattern recognition in nature is generally not the simple process it appears to be in most of our “lab” experiences, but that’s what makes science so interesting! Ball and funnel Fig. 1. Items for radioactive test. Students are presented with a series of 10 relatively common items (Fig. 1): a green plastic cup, a green glass plate, a clear glass plate, a bag of potassium iodide salt, a collection of rocks, a green ceramic plate, an orange Fiesta® Dinnerware cup, a variety of colored glass marbles, an antique jewelry pin, and an Atomic Fireball candy. Students are asked to predict (really just guess this first time) which of these items is radioactive or “hot.” After students have made their initial predictions, the instructor uses a portable Geiger counter with a speaker to demonstrate the radioactivity of each item. The instructor demonstrates first that the green plastic cup is not “hot,” the green glass plate is “hot,” and that the clear glass plate is not “hot.” The students are informed that the glass contains uranium. Students are asked to reevaluate their predictions on the remaining items. The instructor demonstrates that both the salt and the rocks are radioactive, much to the students’ surprise! Students are given a chance to reevaluate the remaining five items based on the prior observations. The instructor then demonstrates that the green ceramic plate is “cold,” but the orange Fiesta Dinnerware cup is extremely “hot.” By now, students are very perplexed! Students are given a final chance to reevaluate their predictions for the remaining three items. The instructor shows students that only the green marbles are “hot,” while Under the pretense of identifying which gender has the largest lung capacity, one male and one female student are asked to come to the front of the classroom. The instructor provides each student with a small clean funnel and a PingPong® ball, and calls for two more volunteers. These students will use a meterstick to measure how high the Ping-Pong ball is blown directly upward. After a signal from the instructor, the two initial students will blow as hard as possible through the funnel so that their ball reaches the highest point. No matter how hard the students blow, the ball will stubbornly spin in place and never become airborne! Of course, this is all an elaborate setup for students to expect the Ping-Pong balls to move upward. At this point, the instructor tells the students that because the air blown by the students moves around the Ping-Pong ball faster than the relatively still air above it, it has less pressure. The pressure difference pushes the ball down and prevents it from leaving the funnel. Color my world Students have many misconceptions when it comes to the nature of color and light. Some of the common ones are that a white incandescent or fluorescent bulb produces light of only one color; that when light passes through a filter, color is added to the light; and that when light passes through a diffraction grating, color is added to the light.16 Using a simple demonstration, we can challenge all of these misconceptions. Students are provided diffraction grating slides, color filter gel sheets (red, green, blue, and possibly yellow), and several flashlights with tungsten filament light bulbs (not LED bulbs). Students are asked to predict what they will see if they observe the white light of the flashlight bulb through the diffraction grating. Many, if not most, will expect the white light bulb to produce only “white” light. They will be surprised to discover that white light appears to contain all of the colors of the rainbow, rather than simply containing only one color (i.e., white light). Next, students are asked to place a color filter between the grating and their eyes. With just two different filters (such as red and blue), it should become obvious to students that color filters actually absorb some colors and transmit oth- THE PHYSICS TEACHER ◆ Vol. 48, NOVEMBER 2010 509 ers, rather than adding color to light. Now, some skeptics may argue that the diffraction grating is adding the rainbow of colors to the otherwise white light. One way to address this is to have students reverse the order of the grating and the filter. If the grating is indeed adding the colors to the white light, then the full rainbow spectrum should reappear if the grating is placed after the light is filtered, right? Students can alternate the order of the grating and the filter and observe that no additional color appears if the grating is placed after the filter. Trying this with at least two color filters should convince skeptics that the grating does not add the color to the light, but rather just spreads out the component colors that comprise white light. The cozy thermometer Students are very familiar with the experience of keeping warm by covering themselves with a “warm” blanket. When the context is changed somewhat, their previous knowledge leads many of them to an incorrect conclusion. During a discussion of heat and temperature, students are presented with a glass thermometer and a small blanket. Students are asked about how they feel when covered by a blanket and then are asked to predict what would happen if the blanket is wrapped around the thermometer. After the temperature is recorded, the thermometer is covered with a blanket and is kept on a nearby table for about five minutes. When the thermometer is unwrapped, the measured temperature is the same as before! A debate promptly ensues, as students reflect on the experience and create alternate explanations. Eventually, they realize that since both the thermometer and the blanket are at room temperature, no heat energy can travel from one to the other. People keep warm when covered with a blanket because it prevents body heat from escaping, not because it provides heat to a person. Both the literature on discrepant events and our experience implementing them in our physical science and physics classes coincide in that this time-tested strategy never ceases to amaze students and to create cognitive conflict by challenging naive but strongly held science conceptions. Although many discrepant events require careful planning and preparation, the pedagogical rewards are worth it! 3. 510 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. J. Park, “Modeling analysis of students’ processes of generating scientific explanatory hypotheses,” Int. J. Sci. Educ. 28, 469–489 (2006). S. Kang, L.C. Scharmann, T. 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Bruce, Learning Social Studies Through Discrepant Event Inquiry, 1st ed. (Alpha Publishers, Annapolis, 1992). 11. W. J. González-Espada, “A last chance for getting it right: Addressing alternative conceptions in the physical sciences,” Phys. Teach. 41, 36–38 (Jan. 2003). Wilson J. González-Espada is an associate professor of science in the Department of Earth and Space Sciences, Morehead State University. He teaches courses in physics, physical science, and science education. Jennifer Birriel is an associate professor of physics in the Department of Mathematics, Computer Sciences and Physics, Morehead State University. Trained as an astrophysicist, she teaches astronomy and physics, and writes the “Astronomer’s Notebook” column for Mercury magazine. Ignacio Birriel is an associate professor of physics in the Department of Mathematics, Computer Sciences and Physics, Morehead State University. Trained as a nuclear structure physicist, he teaches physical science, physics, and nuclear science courses. Morehead State University, Morehead, KY 40351; w.gonzalez-espada@moreheadstate.edu THE PHYSICS TEACHER ◆ Vol. 48, NOVEMBER 2010 511