Schools for Though chapter 5 Science: Inside the Black Box Try answering the following four physics problems. To solve them you need no mathematics, but you do have to understand some basic physical principles. A hint, in case you haven’t worked at physics in a while, is that the problems require using Newton’s First and Second Laws of Motion. The First Law says that if no unbalanced force acts on a body, the body moves uniformly in a straight line. The Second Law says that if an unbalanced force acts on a body, then the force equals the product of the body’s mass and its acceleration. The answers are given in note 1. A coin is tossed in the air and follows the path shown in panel A of figure 5.1. In which panel, B or C, do the arrows correctly show the forces acting on the coin on the upward (a) and downward (b) parts of its trajectory? Figure 5.1 (From Clement 1982. Used with permission of the author and the American Journal of Physics.) 127 Schools for Though chapter 5 Figure 5.2 (From White and Horwitz 1987. Used with permission of Barbara Y. White.) Problem 2. Suppose you are trying to get a hockey puck to travel along the track shown in figure 5.2. At the beginning, somebody hits it in the direction shown. (i) In which direction, A, B, or C, does somebody hit it so that the puck makes the first turn? (ii) In which direction, A, B, or C, does somebody hit it so that the puck makes the second turn? Problem 3 . Under normal atmospheric conditions, an object is placed on a scale and the scale reads 10 pounds (figure 5.3). If the scale and the object were placed under a glass dome and all the air were removed from under the dome, what would the scale read? Problem 4. An object weighing 1 kilogram in normal air takes 1 second to fall a distance d (figure 5.4). How long will it take an object the same size but weighing 5 kilograms to fall the same distance? Figure 5.4 (From Jim Minstrell’s diagnostic quiz. Used Figure 5.3 (From Jim Minstrell’s diagnostic quiz. with his permission.) Used with his permission.) 128 Schools for Though chapter 5 If you didn’t answer all the questions correctly, don’t feel bad. Most people get them wrong. By chapter’s end you will understand these problems and why we tend to make the mistakes we do. These problems appear simple, but they are classic examples from cognitive science and science education of how naive theories or misconceptions dominate everyday reasoning about physical objects. Science educators also know that these misconceptions are hard to change with traditional science instruction. John Clement (1982) was one of the first to study how we reason about the coin problem. He found that what leads us to choose B rather than C is the misconception that flipping a coin gives it an impetus. On the upward path, we reason, the impetus gradually diminishes, until it becomes less than the force of gravity and the coin falls. According to Newton, however, once we toss the coin it would continue on a straight- line path indefinitely unless an unbalanced force acts on it. The only force acting on it is gravity. Gravity causes the coin to slow down until it reaches the top of its trajectory, and then to speed up as it falls back to the ground. Clement found that only 12 percent of students in a first-year engineering course, all high school physics graduates, answered the coin problem correctly. Worse, 72 percent of these students still gave the wrong answer after their first semester of college physics, as did 70 percent after two semesters! Engineering students who persevere through two semesters of college physics are among the most successful science students in our schools. Yet, after all this formal instruction, their naive conceptions of force and motion remained in place. They couldn’t apply Newton’s Laws to simple problems, though they could all, no doubt, recite the laws and write equations for them. The coin problem is not an isolated case, and physics isn’t the only science where misconceptions occur. Cognitive scientists and science educators have examples of misconceptions from the physical and biological sciences at all grade levels-misconceptions that persist through years of science instruction. Cognitive research suggests how science instruction might be improved to correct these misconceptions. It also suggests what must be done to teach science as a high- order skill. The National Assessments show that most students can recall simple science facts, but that serious deficiencies occur at the higher levels of science proficiency. Students are weak in applying the facts they know, interpreting data, evaluating experimental design, and using specialized scientific knowledge to draw conclusions. They are poor at reasoning scientifically, which is to say they don’t really understand science. Most of the examples in this chapter are from physics, but the results, insights, and conclusions generalize to other school sciences. Inside the Black Box A favorite metaphor among scientists is the black box. A black box is a process or phenomenon such that scientists know what goes in and what comes out, but are ignorant of what happens in between. Scientists find black boxes intellectually intolerable; they are obsessed with finding out what goes on inside them. Fred Reif, a physicist and a pioneer in applying cognitive science to improve science instruction, wonders why scientists don’t bring the same obsession to teaching science. “While we make great efforts in physics to understand the mechanisms that underlie observed phenomena,” he writes, 129 Schools for Though chapter 5 “we are often content to consider scientists and students as ‘black boxes’ whose internal intellectual functioning can be left largely unexamined in spite of its importance for teaching” (Reif 1986, p. 48). Reif doesn’t expect physicists to become psychologists, but he feels that science teachers could and should exploit what cognitive science has discovered about how their students think and learn. The cognitive revolution showed that we can make sense of what goes on inside the mental black box. We can begin to understand the mental processes involved in learning and doing science. Effective science instruction has to be sensitive to how long-term memory works. All learning depends on prior knowledge. Learners actively construct understanding by relating current experience, including classroom instruction, to preexisting schemas stored in long-term memory. Just as children spontaneously develop informal math knowledge from infancy, they also spontaneously construct scientific schemas-little theories about how the physical world works. Unlike preschoolers’ informal knowledge of numbers, which is largely consistent with formal school theories, much of their informal, self- acquired science knowledge is inconsistent with formal science. Math education has to build on students’ informal math conceptions. Effective science instruction has to start from student’s informal science conceptions, build on those informal ideas that are consistent with formal science, and correct or eliminate the others. The glimpse cognitive research gives us into the black box can guide science instruction. Researchers have documented scores of scientific misconceptions, and in some cases have traced their development in children. We know much about novice- expert differences in scientific problem solving, especially in physics. We know how differences in what people know and how they organize their knowledge influence their problem solving. Understanding students’ informal, naive ideas gives us a starting point for science instruction, and expert performance gives us an educational goal. Misconceptions and Cognitive Development The development of sophisticated experimental methods has helped developmental psychologists discover how much children, even infants, know about the physical world. Infants can’t speak or even move well; but they can look, and they do so voraciously. Psychologists exploit this trait in a method they call preferential looking. The idea is simple. If you show an infant two objects or displays and the infant consistently prefers to look at one rather than the other, then you can infer that the infant notices some difference between the two objects or displays. Psychologists sometimes elaborate on preferential looking by conducting habituation experiments. They show an infant a display until the infant begins to lose interest in looking at it. They then show the infant a test display. If the infant remains bored with the test display, it apparently sees no difference between the two displays; if the infant looks longer at the test display, it must see some differences. Elizabeth Spelke, a developmental psychologist, studies how infants perceive objects. In one series of experiments, she showed 4month-old infants a display like the first one in figure 5.5, until they began to lose interest in it (Spelke 1990). She then tested the infants with two displays: one showing a single moving rod and the other showing a fragmented moving rod. On average, infants looked twice as long at the fragmented as 130 Schools for Though chapter 5 at the single rod. They found the fragmented rod more interesting; they saw it as different from the habituation display. Spelke reasoned that the infants had created a representation of a single connected rod during habituation. Although they were not able to see such a rod in the habituation display, they inferred that there was a single rod, so the fragmented rod in the test display surprised and interested them. Spelke found the same effect whether the rod in the habituation display moved left-right, up-down, or forward-back.