Structure of Chapters and Activities

The PET curriculum consists of six chapters:

Chapter 1: Interactions and Energy

Chapter 2: Interactions and Forces

Chapter 3: Interactions and Systems

Chapter 4: Model of Magnetism

Chapter 5: Electric Circuit Interactions

Chapter 6: Light Interactions


Each chapter is intended to help students develop a specific set of physics ideas. The physics content of the chapters are described in more detail in the Content section. Here we focus more on the pedagogical structure of the chapters and activities. Each chapter consists of a sequence of activities, and there are two types: Developing Ideas activities and Applying Ideas activities. There is also an extensive set of supporting homeworks.

A typical Developing Ideas activity consists of the following subsections.

To provide a context for discussing the pedagogical structure of a Developing Ideas activity, we will focus on an example: The fourth activity in Chapter 3, called Strength of the Gravitational Force (pdf). We refer to this activity in the following discussion and provide video excerpts from a classroom where students are working on it.

Prior to this activity, students have developed the idea of a field (in the context of making sense of the magnetic interaction), and have been introduced to the gravitational interaction and the gravitational field. The Purpose section and the Key Questions raise the issues of whether the strength of the gravitational force depends on the mass of the falling object, and what other forces, if any, might affect falling objects.

In a previous activity in Chapter 2, students had performed a race between two low friction carts moving along two tracks. Identical fan units powered both carts, but one cart had more mass than the other. The students observed that the more massive cart speeded up and slowed down at a slower rate than the less massive cart.


With this experience (among others) to draw upon, in the Initial Ideas section students consider what happens when a bowling ball and a soccer ball are dropped from the same height. They decide which ball would reach the floor first (or if both reach the ground at the same time).

The Initial Ideas Small Group Video discussion shows part of a long discussion among three students, where they entertain two possible answers to the question and try to draw on previous experience to justify one of them. They finally decide that both the bowling ball and soccer ball will reach the floor at the same time.



The Initial Ideas Whole Class Video shows part of the whole class discussion, where several groups share their prediction and reasoning to the Initial Ideas question. (Each group drew its prediction on a large presentation board and mounted the board in the front of the room.)

Following the whole class discussion, students then worked in their groups on three experiments in the Collecting and Interpreting Evidence part of the activity. During Experiment #1, a student in the group held a 100 g mass in one hand and a 1000 g mass in the other, compared the effort to hold them, and concluded that the gravitational force was greater the object with the greater mass. This led the group to change its Initial Ideas prediction to state that heavier objects will fall faster than lighter objects.

In Experiment #2, however, they dropped several spheres of different masses and reached the conclusion, somewhat surprising to them, that all objects fall together, regardless of their weight.


The Experiment #2 Making Sense Video shows how the group draws on the previous experiment from Chapter 2 (racing cars with the same fan units, but different masses) to help make sense of their observation that all the masses fall together. (The video also includes a segment where the group is explaining their reasoning to the class.)

During Experiment #3 students study the effects of air resistance and conclude that lighter objects and ones with greater surface area are more affected by air resistance than heavier objects with smaller surface areas.

Finally, the Summarizing Questions Video shows a part of the whole class discussion where groups are answering Summarizing Question #3: “If the force of air resistance is negligible, does the rate at which an object falls depend on its mass? Why do you think this is?”1 The groups in the video use slightly different arguments to explain why it makes sense that in the absence of air resistance both heavy and light objects will fall together.

A typical Applying Ideas activity begins with students comparing the ideas they developed during class with Scientists’ Ideas. Except for some jargon, students generally develop conceptual ideas that are essentially the same as those listed in the Scientists’ Ideas handout. Students are also asked to summarize the experimental evidence that would support each idea.

Following the comparison of ideas, students apply their ideas to explain some interesting phenomena. The curriculum provides a structure for constructing explanations: First, analyze the situation by identifying the interacting objects and drawing energy and/or force diagrams; second, write an explanation using the ideas developed in class; and third, evaluate the explanation using a set of criteria. Students practice evaluating explanations written by other hypothetical students and then construct their own. See the Common Themes page for a more detailed description of explanations.


1This question is worded slightly differently in the current version of PET: "If the force of air resistance is negligible, does the rate at which a falling object's speed increases depend on its mass? Why do you think this is so?"