Description of Chapters

The PET course consists of six chapters of activities. The course is hierarchical, with both topics and skills developed in a structured progression around some powerful common themes.

Chapter 1: Interactions and Energy

The first chapter introduces students to all of the common themes of the course. The concept of interactions is first introduced in the context of three different types of interactions.


Students use motion sensors and graphing software to investigate the motion of objects in these interactions, and then use a computer simulator to determine the effect of removing friction completely. From their results, they infer that the effect of such interactions is to change the motion of an object in some way.


In parallel, they are also introduced to an energy description for interactions that can be easily represented in diagrammatic form.

In preparation for the idea of energy conservation, students explore two interactions between objects of different temperatures:

In this context, students are introduced to the idea of  interaction chains, such as when hot water warms up a glass, which then emits infrared radiation that is absorbed by an IR camera. Using this idea, students consider the interactions that result from changes in temperature, such as those caused by the friction contact interaction, and develop the idea that the heat conduction and infrared interactions are pervasive.  Finally, by keeping careful track of energy inputs, outputs, and changes, in various simulator set-ups students construct an energy conservation rule applicable to both open and closed systems:

Energy Input = Energy Output + Energy Changes within the System

After they have developed their ideas, students are introduced to a procedure that they use to construct and evaluate energy-based explanations of various phenomena.

Chapter 2: Interactions and Forces

This chapter introduces students to an alternative framework (that of forces) within which they can explain the same contact interactions they first saw in Chapter 1. Chapter 2 is written to explicitly address common misconceptions many students hold about the nature of forces and their connection to the motion of an object.

Students again use motion sensors and computer simulators to gather evidence on the effect that a single force has when it is applied to a cart under various conditions. From this evidence they construct a set of ideas that is equivalent to Newton’s first two laws of motion. The ideas are extended to combinations of forces in a homework assignment. These ideas are then applied in constructing force-based explanations for phenomena.

In this chapter students are also introduced to the ideas of elementary students about forces, with two Learning about Learning assignments (one carried out in class, the other as homework).

Chapter 3: Interactions and Fields

The first activity in this chapter uses the context of the interaction between two magnets to allow students to consider ‘action at a distance’. The activity then introduces the idea of a ‘field of influence’ to account for this phenomenon, and to act as a source or receiver of energy during such interactions. Students are also introduced to the idea of potential energy. 

In the second activity, students consider the same ideas in the context of the electric charge interaction. In a LAL homework, they consider the relationship between observations and models. In the rest of the chapter, students consider the gravitational interaction using both energy and force frameworks. They examine the interplay between stored energy and motion energy, and explicitly address the apparent paradox of different mass objects falling at the same rate.


Chapter 4: Model of Magnetism

This chapter concentrates more on the nature of science as it engages students in a series of activities designed to lead them to a basic domain model of magnetism. After examining the phenomenology of magnetic interactions between magnets and ferromagnetic materials, students propose an initial model for what happens inside a nail when it is magnetized by rubbing with a permanent magnet.

In the following activities, students make predictions based on their model and perform experiments (such as cutting a magnetized nail into two pieces) to test them. They then try to patch or revise their model as needed to explain their new observations.  Watch a video of students explaining their magnetism models.

At the end of the chapter, students complete a special homework assignment in which they examine the nature of science in the context of the process they went through to develop their magnetism model, along with other ideas they have developed in the PET course. In the same context of developing a magnetism model, students also examine the historical development of a model of magnetism and elementary students' ideas about magnetism.

Chapter 5: Electric Circuit Interactions

Students first investigate the conditions necessary for a simple electric circuit to work. In an optional experiment, they can apply their ideas to explain the internal construction of a flashlight. They then consider the energy flow in circuits with different energy sources and receivers. 

In addition, students examine series and parallel circuits in a homework assignment involving the use of a computer simulator.

Experience has shown that students have difficulty differentiating between the ideas of energy flow and current flow in a circuit.  Therefore, the third activity in this chapter explicitly addresses the idea of electric current. The fourth activity explores the special case of energy flow in short circuits.  After developing their own ideas about current flow in a circuit, students examine young children’s ideas on the same topic. 

Students next explore energy efficiency in the context of electrical devices using their knowledge of electric circuits and energy conservation. In the culminating activity for this chapter, students construct and analyze ‘The Fabulous Wake-up Machine’, a single-battery circuit capable of powering a bulb, a buzzer and a fan motor simultaneously.

Chapter 6: Light Interactions

In the first activity of Chapter 6, students explore how light interacts with mirrors, and determine whether light interacts with their eyes. Then, in the second activity, they examine elementary students' ideas about the relationship between light and seeing, and how those ideas evolve after the children engage in experiments similar to those the PET students performed in the preceding activity. 

Students then investigate how light reflects from shiny and non-shiny surfaces, and how refraction occurs. The fourth activity deals with the color spectrum of visible light and reflection from colored objects, and in the final activity, students explain phenomena involving light and color using the ideas they have learned in this chapter.

During this chapter, students also complete a ‘learning about learning’ assignment that allows them to reflect on the learning process itself and their own personal learning during the course. This assignment is followed by the last homework assignment, in which students review social scientists' ideas about learning science and decide to whom they apply: themselves, children, and/or scientists. This homework becomes the basis for a discussion about the learning process during one of the final class periods.