## Pedagogy

Each SC activity consists of four sections. The Purpose includes a brief introduction and a key question that will be answered during the activity. The Initial Ideas section is designed to elicit students' prior knowledge about the central issue of the activity. Both in the small-group and in the whole-class discussion that follows, students usually suggest ideas and raise issues that are explored later. The Collecting and Interpreting Evidence section includes experiments, and a sequence of questions to prompt students to compare their experimental observations with their predictions. The choice of questions was informed by the extensive literature on students' understanding of physical science. Often, the experimental evidence supports some of the students' initial ideas but not others. The Summarizing Questions section addresses the activity's key question, helps students recognize what they have learned in the activity and how their final ideas might have built on their initial ideas.

As an example of the SC activity structure— and the way the Next Gen PET Design Principles are incorporated—consider Activity 1 from the Force Model Unit of the Interactions and Forces Module. The Purpose section reminds students that, in a previous unit, they described contact push/pull interactions in terms of energy. In Unit FM, it is explained that similar interactions will be described in terms of pushes or pulls, which are called forces. The activity is guided by the key question, When does a force stop pushing on an object?

The Initial Ideas section asks students to think about a soccer player kicking a soccer ball. After the kick, the ball rolls across the grass and gradually comes to a stop. This question follows from Design Principle 1 (Learning builds on prior knowledge). Students sketch a speed-time graph for the motion of the ball from the moment the player's foot first comes in contact with the ball until it comes to a halt again. They then label on their graph where the foot was in contact with the ball and where there was a force pushing the ball forward. Finally, they draw pictures of the ball and show what forces (if any) they think are acting on the ball during the kick and also after the foot has lost contact with it, but before it stops. Student groups answer these questions, sketch graphs and drawings on large white boards, and then share their thinking with the whole class. The pedagogical purpose is to immediately begin addressing the common idea that 'force' is something that an object carries along with it and is transferred between objects when they contact each other [1-5]. For instance, it is not uncommon for students to draw an arrow on the after-the-kick picture representing the force from the kick. Compared to physicists, students often ascribe a different meaning to the word 'force,' and often talk about the 'force of an object,' as if it were a property of the object. This activity provides students with evidence that a force is an interaction between two objects, not something carried by an object or something associated with an individual object.

The Collecting and Interpreting Evidence section consists of an experiment using carts, tracks, and motion probes, and several questions to answer. Before the experiment, students are first shown a speed-time graph for a cart receiving three quick pushes. They are asked to sketch a corresponding force-time graph for the motion. Next, students set up a motion detector and a low friction cart with a force sensor to collect speed-time and force-time data. They record data as they give the cart three quick pushes as it moves along a track. The subsequent observation and making sense question asks students whether there is a force acting on the cart in the periods between pushes. This supports the norm that arguments in science should be based on evidence (Design Principle 5: Learning is facilitated through the establishment of norms). To focus the students' attention on the relationship between the motion of the cart and whether or not there is a force acting on it, the activity provides the following conversation between three hypothetical students.

Samantha:
The force of the hand is transferred to the cart and is carried with it. That's why the cart keeps moving after the push.
Victor:
The force of the hand stops when contact is lost, but some other force must take over to keep the cart moving.
Amara:
After contact is lost there are no longer any forces acting on the cart. That's why it moves differently.

Students discuss which of the three hypothetical students they agree with and why. This question usually elicits substantive discussion, since the three hypothetical students express commonly held views about the relation between force and motion.

The Summarizing Questions section consists of four questions. The first question asks what happens to the motion of a cart when a force acts on it. The second question asks whether force is transferred from the hand to the cart during the interaction. The third question asks at what point the force stops acting on the cart when it is given a quick shove. The last question asks what is transferred from a source to a receiver during a contact push/pull interaction: energy, force, both, or neither. This last question tends to generate much discussion since it requires students to tease apart the separate concepts of force and energy. For each Summarizing Question, students are expected to explain their reasoning and, where appropriate, to cite evidence from the activity to support their answer.

Activity 1 illustrates how Next Gen PET incorporates the Design Principles Students' prior knowledge is elicited through questions in the Initial Ideas section (supporting Design Principle 1), providing opportunities for students to engage in discussions (supporting Design Principle 4). Carts, sensors, and computers, along with whiteboards and the student workbook, are tools that facilitate learning and help structure interactions (Design Principle 3). Next Gen PET also promotes norms (Design Principle 5) that ideas should be supported by experimental evidence, that scientific ideas should make sense, that students need to take an active role in learning, and that students are expected to contribute ideas to group and class discussions. On a larger scale, Activity 1 is part of a Unit that successively builds the complex ideas associated with force and motion (Design Principle 2).

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This project is funded by the National Science Foundation IUSE program, DUE-1626496. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.