Conceptual Storyline
Physics in Action (Sports 2)
Conceptual Storyline Overview:
The purpose of a conceptual storyline is to help students to see how all of the activities in a chapter are connected. Without a conceptual storyline, Active Physics can appear to students as a series of disconnected, hands-on activities. Students might have fun and they might learn scattered bits of knowledge, but they don’t learn “facts and ideas in the context of a conceptual framework”, one of three major foundational principles of learning identified by the National Research Council in its book, How People Learn.
The conceptual storyline for the Physics in Action chapter focuses on unfolding student understanding about how objects move. The teacher should focus conceptual debriefs after each For You To Do on helping the students to see how the experiment they just completed adds on to their prior understanding of an object’s motion. The teacher can connect this discussion to deep understanding of physics, including Newton’s Laws and quantitative representations of the concepts, but the teacher needs to be careful that the students don’t get lost in those details. The teacher should consistently guide the students back to the big picture of answering the question, “How do objects move?”
The Laws of Motion map from Atlas for Science Literacy provides key insight on the interrelationships of key concepts involved in this chapter. This tool can help teachers to visualize the conceptual ecology that they are guiding students to construct throughout the chapter. Atlas includes a terse, clear discussion of student misconceptions that impede students’ understanding of the key concepts related to the motion of objects. A similar discussion can be found on-line in section 4f of the research base of Benchmarks for Science Literacy. Greater depth on student’s misconceptions about forces and motion is covered in chapters 21 and 22 of Making Sense of Secondary Science: Research into Children’s Ideas (Driver et. al., 1994, Routledge Farmer Publishing).
Conceptual Storyline and Scaffolding Questions:
The following table gives for each activity the key concept, the key experimental evidence, and questions teachers can ask to help students link the evidence with the explanations provided by the concepts. The purpose of the questions is not to provide a script for teachers to follow. Guiding and facilitating learning, especially orchestrating discourse, following the vision of the national standards can’t happen via a script. Instead, these questions are designed to provide a scaffold to help teachers begin the process of orchestrating discourse successfully.
A / Key Experimental Evidence[1] / Questions for Focusing on Experimental Evidence /Key Concept
/ Questions for Focusing on Concepts1 / Data table from step 1a / Is the motion of the ball up the far side of the bowl the mirror image of the ball’s downward motion? If there were no friction, do you think it would be a perfect mirror image? / An object’s motion[2] stays the same unless acted on by an unbalanced force. / What forces[i] were causing the balls in experiment to speed up? What forces were causing them to slow down?
Think about an object that’s moving at a constant speed. What would happen to its motion if no forces acted on it?[ii]
5c, 6b, 8a / Would it be logical to conclude, that in the absence of friction, the ball in step 8 should keep going?
2 / 6a, 7a / What differences did you notice in the tennis ball’s motion as you increased the force you put on it? / An object’s acceleration is directly proportional to the unbalanced force acting on it and inversely proportional to its mass. / What does directly proportional mean? Which factor from our experiment had a direct relationship on acceleration?
What does inversely proportional mean? Which factor had an inversely proportional relationship with acceleration.
9a, 10a, / What differences in motion did you notice when you applied the same force to objects of different mass?
3 / 4a, 5a / [Guide a discussion of the questions posed in 4a and 5a.] / Predicting the motion of an irregularly shaped object is easier if you focus on its center of mass. / [Have students first complete Reflecting on Activity and Challenge.] What are some sports events for which focusing on the athletes’ centers of mass would make predicting their motion easier than looking at their whole body?
4 / 1c, 2b / How is the idea of hang time a myth? Why do you think people believe in hang time when your data shows that there’s no such thing? / If an object is launched straight up, the height of its trip can be predicted from its launch speed and mass or from the work done in launching it. / Think about some sports applications of what you’ve learned. How could take what you’ve learned in the lab and use it for predicting what happens in certain sports events?
6b, 7a / [Have each group post a summary of their data and calculations. Guide a discussion by which the each group analyzes the work of the other groups, looking for strengths and weaknesses.]
5 / 1e, 2c / Do you think forces always come in pairs? / If object A is applying a force on object B, then B is applying an equal and opposite force back on A. / Forces always come in pairs. Why is this a surprise to most people who haven’t studied physics?[iii]
3b, 4b / One student said, “If you’re not going up or down, then the ground has to be pushing up at the same amount your weigh pushes down.” Would you agree, based on your findings?
6 / 1c, 2a, 4b / Compare your findings for steps 2, 3, and 4. When did µ change? When did it stay the same? / Friction has to be considered when describing an object’s motion. Horizontal sliding friction is proportional to the roughness of the surface and the mass of the object. / What are the factors that affect sliding friction? Is their relationship to sliding friction direct or inverse?
7 / 3a, 4a, 5a, 6a, 7a / Compare and contrast what you discovered about collisions. What general principles do you think you’ve found? / An object’s momentum is proportional to its mass and velocity. / What are the factors that affect momentum? Is their relationship to momentum direct or inverse?
8 / 1a / What patterns did you notice in the data from the table in step 1? / In the collision of two objects, their total momentum is the same before and after. / If you repeated this experiment again and again so that you could do it without any error, what pattern do you think you’d see in your table from step 3?
9 / 1a / What did you find out about the direction of the force when an object is moving in a circle? Do you think this is true for all circular motion? / If an object is moving in a circle, a force must be acting on the object toward the center of its orbit.[3] / Think of some sports situation in which an object is moving in a circle. What is providing the centripetal force? What is the object’s path when the centripetal force is removed?
3 b, 3c, 3d / [Debrief directly to the questions included in the steps.]
[1] All step numbers are from FYTD, unless otherwise indicated.
[2] Rest can be considered a type of motion (velocity = 0).
[3] Based on Benchmarks for Science Literacy #4F/3.
[i]Per the research base of Benchmarks, “Students hold various meanings for the word "force." Typically, students think force is something that makes things happen or creates change. Their descriptions of force often include related words such as energy, momentum, pressure, power, and strength. Younger students associate the word "force" with living things (Watts, 1983b). Students tend to think of force as a property of an object ("an object has force," or "force is within an object") rather than as a relation between objects (Dykstra, Boyle, & Monarch, 1992; Jung et al., 1981; Osborne, 1985). In addition, students tend to distinguish between active objects and objects that support or block or otherwise act passively. Students tend to call the active actions "force" but do not consider passive actions as "forces" (Gunstone & Watts, 1985). Teaching students to integrate the concept of passive support into the broader concept of force is a challenging task even at the high-school level (Minstrell, 1989).”
[ii] Per the research base of Benchmarks, “Students believe constant speed needs some cause to sustain it. In addition, students believe that the amount of motion is proportional to the amount of force; that if a body is not moving, there is no force acting on it; and that if a body is moving there is a force acting on it in the direction of the motion (Gunstone & Watts, 1985). Students also believe that objects resist acceleration from the state of rest because of friction—that is, they confound inertia with friction (Jung et al., 1981; Brown & Clement, 1992). Students tend to hold onto these ideas even after instruction in high-school or college physics (McDermott, 1983). Specially designed instruction does help high-school students change their ideas (Brown & Clement, 1992; Minstrell, 1989; Dykstra et al., 1992).”
[iii] Per the research base of Benchmarks, “Students have difficulty appreciating that all interactions involve equal forces acting in opposite directions on the separate, interacting bodies. Instead they believe that "active" objects (like hands) can exert forces whereas "passive" objects (like tables) cannot (Gunstone & Watts, 1985). Alternatively, students may believe that the object with more of some obvious property will exert a greater force (Minstrell, 1992). Teaching high-school students to seek consistent explanations for the "at rest" condition of an object can lead them to appreciate that both "active" and "passive" objects exert forces (Minstrell, 1982). Showing them that apparently rigid or supporting objects actually deform might also help (Clement, 1987).”