Using coherent storylines to explain phenomena

Transcription

1 Using coherent storylines to explain phenomena Renee Turley, Alan Trotochaud, and Todd Campbell This space shuttle launch carried astronauts John Young and Robert Crippen into an Earth orbital mission. NASA September

2 Sense-making has been described as working on and with ideas both students ideas and authoritative ideas in texts (Campbell, Schwarz, and Windschitl 2016) to build coherent storylines, models, and/or explanations. In this article, we describe our process for developing storyline units to support students making sense of and explaining a rocket launch. Storylines The storyline approach, which aligns with the Next Generation Science Standards (NGSS Lead States 2013; see box, p. 41), engages students in figuring out instead of learning about. The storyline approach features three key dimensions: an anchoring phenomenon chosen to spark questions, investigations that allow students to figure out parts of the story, and a culminating performance expectation that puts the story together. Coherence is emphasized in storylines as students build ideas over time (Reiser, Novak, and Fumagalli 2015). The Chemical Reaction, Energy, and Force storyline For this storyline s anchoring phenomenon, we chose a specific portion of a rocket launch and articulated our own explanation of it (Figure 1). We then constructed a storyline to guide the day-today activities of the unit (Figure 2, p. 38). Initially, we developed the storyline by predicting questions students might ask. Each predicted question was then used to identify potential experiences (e.g., investigations, demonstrations) that students could use to explain the anchoring phenomenon. Each question represents a row in the storyline (Figure 2), and each row concludes with students figuring out something related to the rocket launch. Each row also leads to another question in the next row. Day 1: Students initial explanations To begin the unit, we showed students a video clip of the rocket launch (see On the web ) and asked them to share initial ideas about how a large rocket can be lifted off the ground. After whole-class discussion, students worked in groups of two or three to develop an initial model that explained their ideas about the rocket launch. Groups shared their models in FIGURE 1 Teacher explanation of the anchoring phenomenon (rocket launch). At first, chemicals used during rocket liftoff are in a less-reactive (stable) state, as can be seen in gases flowing out without any noticeable reaction. These chemicals (the fuel), like all matter, inherently have energy related to forces of protons and electrons of neighboring atoms. The bond energy between atoms is one type of energy. In some cases, matter can change without any added energy other than that taken from the surrounding environment for example, the chemical reaction of baking soda with vinegar. In other cases, additional energy is required to destabilize the reactants and allow them to change. Just before rocket liftoff, sparks are applied to the fuel to provide this energy (the activation energy). In a reaction that releases energy, the difference between the energy of the products (H 2 O) and the energy of the reactants (H 2 and O 2 ) results in excess energy being released into the environment [exothermic reaction]. At the particle level, it takes less energy to break the bonds in H 2 and O 2 molecules than that released when the new bonds in H 2 O molecules form. This energy is released into the environment as heat, light, and sound. Once the reaction starts, the sparks can be removed because some of the released energy causes more hydrogen and oxygen atoms to rearrange into water (similarly, once a fire starts, you don t have to continue adding outside energy [heat] to keep the flame going). To make the rocket launch, the chemical reaction takes place in a reaction chamber outside the fuel tank, where the gases are released at a controlled rate (not too fast or too slow). The released energy in this exothermic combustion reaction causes the gas molecules to move faster, raising pressure, which causes the primary product (H 2 O vapor) to expand and exit from the downward-facing nozzle. The gas flowing out of the nozzle has mass, and its downward movement creates a force (Newton s second law, F=ma). When something moves in one direction, there is an opposing force in the opposite direction (Newton s third law). This creates the force that pushes the rocket upward and into space. The United Launch Alliance Atlas V rocket with NASA s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft launches from the Cape Canaveral Air Force Station Space Launch Complex 41. NASA/BILL INGALLS 36 The Science Teacher

3 Achieving Liftoff Space Shuttle Columbia lifts off from Kennedy Space Center. NASA another whole-class discussion, then we elicited questions about the phenomenon. Next, we took up one of the questions that emerged: What is fuel? (Figure 2, Row 1, p. 38). Days 2 5 (Row 1): What is fuel? Through three investigations/activities, students began to develop an explanation to answer the Row 1 question (see On the web for detailed directions, resources, and safety information for these activities). During the first investigation, students tried to burn various materials (e.g., wooden splint, paper, nail) to determine why some materials burn and others do not. Students, who had previously learned about matter, were prompted to think about and represent (through developing initial group models) what might be happening at the particle level (i.e., atoms and molecules) when something burns. They thus began to consider the role that chemical bonds play in combustion. Through this investigation, students came to the consensus that fuel is made of matter, which is made up of small particles (atoms), and different types of matter contain atoms that are differently connected. During the second investigation, students completed a matter scavenger hunt using information communication technologies (ICTs) (e.g., online search engines) and other available resources to find examples of matter that occur in nature as single atoms. Students discovered that most matter in nature is made up of combinations of atoms, and few examples of individual, unconnected atoms exist. During the third investigation, we introduced students to the concept of bond energy (the energy required to break a chemical bond), gave them bond energy diagrams and tables (see On the web ), and asked them to make observations about the relative energies of single atoms versus bonded atoms. Through this investigation, students concluded that bonds involve energy, and that when atoms bond, they generally become more stable (lower potential energy). From these experiences, the question that guided Row 2 emerged. Days 5 8 (Row 2): Why do some things react and others do not? To answer this question, students engaged in two investigations/activities (see On the web for detailed directions). First, students were asked to reflect that both the wooden splint and paper burned in the first Row 1 investigation, and the nail did not. The first investigation for Row 2 involved live and video demonstrations showing an iron nail, steel wool, and magnesium metal strips reacting with oxygen from the air and the energy of a Bunsen burner s flame (see On the web for safety information). Students then considered the fact that some reactions occur more quickly or robustly than others (e.g., Mg vs. Fe during the flame demonstration) and that when new combi- September

4 FIGURE 2 The Chemical Reactions, Energy, and Forces storyline. Anchoring phenomenon/question Rocket launch: What happens during the launch of a shuttle to allow it to leave Earth and enter space? Activities/Science and Engineering Practices (SEPs) Students are introduced to the phenomenon and asked to develop initial models (SEP). Students share initial models and develop a list of unresolved questions about the phenomenon. (What is fuel?) Question Activities/investigations/SEPs What we figured out/what questions (Q) remain Row 1: What is fuel? Observing whether different materials burn. Using ICTs to conduct a matter scavenger hunt. Examining bond energy data. Fuel is made of matter. Matter is made of small particles (atoms) that are connected together. The tighter the atoms are held together, the more heat or energy is required to break their bonds and rearrange them. Q: Why do some things react whereas other things do not? Row 2: Why do some things react whereas other things do not? Row 3: What role does energy play in the rearrangements of atoms, and where does the energy come from? Demonstrating that Mg reacts with a flame, but Fe does not. Students develop an atomic model to explain what causes the observed differences between Mg and Fe. Demonstrating reactions that do and do not react (a napkin on a table does not burn, even though it is exposed to oxygen). Designing experiments with baking soda and vinegar at room temperature and colder, or glow sticks in cold and hot water, to help explain activation energy. Atoms are held together more or less tightly in different materials, and heat or energy is needed to break them apart. Some bonds require more heat/energy than others. Particles in different materials are held together with different amounts of energy. Q: What role does energy play in causing the rearrangements of atoms, and where does the energy come from? Reactions need a certain amount of energy to allow atoms to rearrange (activation energy). The materials that have been rearranged have a different amount of energy holding them together than the original materials. Some of the energy released is used to keep the rest of the reaction going. Q: What makes the rocket lift off if fire by itself does not cause liftoff? Row 4: What makes a rocket lift off if fire by itself does not cause liftoff? Doing investigations with balloons attached to a straw and smooth string to learn more about what creates a force that causes movement. Tossing a weighted ball from a rolling chair to learn more about equal and opposite actions/reactions of forces. Summative assessment The flow of gas released pushes down, so the rocket is pushed up. Using what they figured out in rows 1 4, students develop a final explanatory model for a space shuttle liftoff. 38 The Science Teacher

5 Achieving Liftoff nations of atoms form, energy is released as atoms rearrange to form more stable product atom combinations. Because it was difficult for students to explain what happens to these metals in the flame, we spent additional time teaching about metallic bonds. Through this investigation, students began to develop ideas and questions about the ways in which atoms are held together tightly or loosely, depending on the compound or metal. They also learned that the amount of heat or energy needed to break atoms apart is correlated with how tightly the atoms are held together by bonds. During the second Row 2 investigation, students were introduced to reactions that occur without the energy of a flame s heat (e.g., thermite reaction, steel wool reacting with a battery, glow stick). After observing these reactions, students thought about how chemical reactions can occur without added heat. From these investigations, the question guiding Row 3 emerged (Figure 2). Days 9 12 (Row 3): What role does energy play in the rearrangements of atoms, and where does the energy come from? To answer this question, students engaged FIGURE 3 in two investigations/activities (see On the web for detailed directions). During the first Row 3 investigation, students compared a napkin on a table being exposed to oxygen but not burning to a napkin in an oven being exposed to oxygen and burning. Students then designed experiments to observe baking soda and vinegar or glow sticks reacting at different temperatures, which helped them understand the relationship between particle energy and chemical reaction rates. Both activities helped students reconsider the rocket launch video, as they applied what they had learned about the role and origin of energy in rearranging atoms to the space shuttle s fuel and the presence of sparks during the launch. At the conclusion of these investigations, students revised their original models to include what they learned from all the activities about what fuel is, why some things react and some things do not, and the role and origin of energy in rearranging atoms. At this point, students realized that their explanations were becoming more sophisticated, but a question remained and was addressed in Row 4. Days 13 and 14 (Row 4): What makes a rocket lift off if fire by itself does not cause liftoff? To address this question, students engaged in two investigations/activities to develop an understanding that forces act in balanced pairs, such that for every action there is an opposite and equal reaction (Newton s third law). They also learned how forces are applied to an object such as a rocket to cause a specific movement or trajectory (see On the web for detailed directions). During the first Row 4 investigation, students were shown a failed rocket launch in which all of a rocket s energy was released at once, resulting in the rocket being consumed in flames. They used balloons taped to straws, which moved along a horizontal string hung in the classroom, to determine the most efficient way to release stored energy and move the balloon the greatest distance. During the second investigation, students were shown an action/reaction phenomenon (i.e., a person in a rolling chair Example of a final student model. September

6 Energy that is released causes changes in matter, in this case the expulsion of product gases, which creates the force needed to launch the rocket (Newton s third law). Conclusion Bell and Shouse (2014) acknowledge that there are many different instructional models that can be used in aligning instruction with the NGSS. Our work with the storyline approach (Reiser 2014; Reiser, Novak, and Fumagalli 2015) helped us learn more about one recently developed model. This work has provided us a context for professional learning as we not only developed a useful resource for engaging our students but also learned more about the structure of the NGSS. Renee Turley (rturley@cromwell.k12.ct.us) is a science teacher at Cromwell High School in Cromwell, Connecticut; Alan Trotochaud (atrotochaud@eosmith.org) is a science teacher at E.O. Smith High School in Storrs, Connecticut; and Todd Campbell (todd.campbell@uconn.edu) is an associate professor of science education at the University of Connecticut in Storrs, Connecticut. NASA Space shuttle Discovery and its seven-member crew begin the STS-121 mission. throwing a weighted ball and moving backward as the ball moved forward) and explained how it might be related to the rocket launch. At this stage, students had the necessary tools, resources, and ideas to explain how the space shuttle lifts off. Day 15: Students final explanations On the last day, students completed a final version of their explanatory models showing how a large rocket lifts off (see On the web for assessment resources and examples of student work). Although students final models varied, most students included the relevant disciplinary ideas in the work (see Figure 3, p. 39, for a sample final model): Fuel is necessary. Fuel is made of chemicals that are made of bonded atoms. Chemical reactions rearrange atoms that are bonded together. Chemical reactions occur when the breaking and reforming of bonds cause a change in overall energy. Energy is necessary to break bonds (e.g., activation energy or sparks during a rocket launch). Energy is released when new bonds form. On the web Assessment resources and examples of student work: Bond energy data set (diagrams and tables): Row 1 activities information: Row 2 activities information: Row 3 activities information: Row 4 activities information: Safety information for these investigations: Space shuttle launch video: Storyline: References Bell, P., and A. Shouse Practice Brief 4: Are there multiple instructional models that fit with the science and engineering practices in NGSS? (Short answer: Yes.). STEM Teaching Tools: Teaching Tools for Science, Technology, Engineering and Math (STEM) Education. Campbell, T., C. Schwarz, and M. Windschitl What we call misconceptions may be necessary stepping-stones on a path toward making sense of the world. The Science Teacher 83 (3): NGSS Lead States Next Generation Science Standards: For states, by states. Washington, DC: National Academies Press. Reiser, B.J Designing coherent storylines aligned with NGSS for the K 12 classroom. Paper presented at the National Science Education Leadership Association, Boston. ly/1tzesag. Reiser, B.J., M. Novak, and M. Fumagalli NGSS storylines: How to construct coherent instruction sequences driven by phenomena and motivated by student questions. Paper presented at the Illinois Science Education Conference, Tinley Park, IL The Science Teacher

7 Achieving Liftoff Connecting to the Next Generation Science Standards (NGSS Lead States 2013). Standards HS-PS1 Matter and Its Interactions HS-PS2 Motion and Stability: Forces and Interactions Performance expectations The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid connections are likely; however, space restrictions prevent us from listing all possibilities. The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations listed below. HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. Dimension Name and NGSS code/citation Specific connections to classroom activities Science and Engineering Practices Disciplinary Core Ideas Developing and Using Models Use a model to provide mechanistic accounts of phenomena. Analyzing and Interpreting Data Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution. Constructing Explanations and Designing Solutions Construct an explanation based on valid and reliable evidence obtained from a variety of sources (including students own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. Engaging in Argument From Evidence Evaluate the claims, evidence, and reasoning behind currently accepted explanations or solutions to determine the merit of arguments. PS1.B: Chemical Reactions Chemical reactions, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy (HS-PS1-4). A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart (HS-PS1-4). Throughout the unit, students iteratively develop models of a rocket launch. Students analyze and interpret data collected from experiments and use these analyses to inform revisions of their models. Students use evidence from observations and experimentation to explain different characteristics of chemical reactions and forces. Students evaluate other students claims, evidence, and reasoning for the arguments made about their models, which include data collected from experiments. Students explain how atom rearrangement and subsequent released energy is used to launch a rocket. Students observe that some compounds are stable and require energy if their atoms are to be rearranged. Crosscutting Concepts Energy and Matter The total amount of energy and matter in closed systems is conserved. Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. Students examine changes in energy and matter specifically related to chemical reactions, the amount of energy necessary to activate a chemical reaction, and the amount of energy released during atom rearrangement in rocket fuel. September