Contents related to energy and sustainable development are all in compulsory Section 3 in each version of textbooks, but the chapter placement is different. Therefore, this paper compares the chapter introducing energy and sustainable development, as shown in Table 1.

As can be seen from Table 1, in terms of the chapter headings in which energy and sustainable development are located, the People’s Education edition is electricity energy and the energy conservation law, the title of the Guangdong edition is Electricity and sustainable development of energy, and the title of the chapters in the remaining four versions is energy and sustainable development.

The People’s Education edition has the least knowledge capacity of energy and sustainable development with a total of 4710 characters, the Shanghai Science and Education edition has the most knowledge capacity with a total of 15,123 characters, and the Luke edition, Guangdong edition, Education Science edition, and Shanghai Science and Technology edition have 7414, 8922, 11,321, and 13,078 characters, respectively. In terms of the subsections of the content on energy and sustainable development, the People’s Education edition has fewer subsections, occupying only one subsection, with a clear knowledge line and easy for students to understand. The other versions of the textbook divided the content into subsections, with the difficulty of knowledge ranging from shallow to deep, among which, the Shanghai Science and Education edition divided it into four subsections, and the remaining four versions of the textbook divided it into three subsections.

Reviewing the textbooks of the six editions, we found that the “Energy and Sustainable Development” of the People’s Education edition, and the Luke and the Guangdong edition are preceded by circuits and their applications, followed by electromagnetic fields. Shanghai Science and Education edition, Education Science edition, Shanghai Science and Technology edition textbook “Energy and sustainable development” is located in the last chapter of Compulsory Study 3, the front content of the circuit and its application and electromagnetic fields and electromagnetic waves. Six versions of the textbook are the knowledge of the circuit to the front, for the study of energy and sustainable development in the “Energy Conservation Law” part of the content to lay the foundation, for the cognitive laws of students.

All six versions of the textbook include three parts of knowledge: “Transformation and Conservation of Energy”, “Classification and Utilization of Energy”, and “Energy and Environmental Protection”. The order of presentation is shown in Table 2.

Knowledge points are organized from light to deep, reflecting the logic between knowledge [2] [3] . As can be seen from Table 2, the textbooks of People’s Education edition, Shanghai Science, and Education Science edition first arrange the transformation and conservation of energy, and then arrange the classification and use of energy, and this arrangement begins with the student’s existing experience, and it is explained to the students in detail through theoretical knowledge of the energy conservation law that, although the total amount of energy does not appear to be infinite [4] . The remaining three versions of the textbook arrange the classification and utilization of energy before the transformation and conservation of energy, weakening the logic between the two parts of knowledge. In the Shanghai Science and Education edition, energy use is included in the environmental protection section, while in the Guangdong edition, energy classification is included in the environmental protection section.

Different versions of secondary physics textbooks have slightly different ways of understanding “energy and sustainable development”, but they all meet the requirements of the curriculum standard from the perspectives of energy conversion and conservation, energy classification and use, and energy and environmental protection. Each version of the textbook has its characteristics, for example, the secondary headings of the Shanghai Science and Technology edition

textbook are provided in the form of questions; The Luke edition and the Education Science edition textbook pay more attention to the investigation of each knowledge point; The People’s Education edition, the Shanghai Science and Education edition and the Guangdong edition textbook emphasize more on the connection of knowledge and the systematization of knowledge [5] .

A comparison of the six versions of the textbook reveals that there is no definition of “energy” in the People’s Education edition and Luke edition, and it is a bit abrupt to categorize energy directly. The other four versions of the textbook first define the concept of “energy”, and then describe the classification of energy and its application, which is in line with students’ cognition.

Regarding the section on “Classification of energy sources”, different textbooks take different approaches to categorization. The People’s Education edition and Shanghai Science and Education edition classify them into renewable and non-renewable energy sources and give common examples. In terms of the comprehensiveness of the classification of energy sources Guangdong and Shanghai Science and Technology editions do a better job. In addition to the common classification of primary energy sources (including renewable and non-renewable energy sources) and secondary energy sources, the Guangdong edition also classifies energy sources into polluting energy sources and clean energy sources according to whether or not the energy sources pollute the environment, while Shanghai Science and Technology edition introduces the classification method according to the source, nature and utilization technology of the energy sources. Other editions of the textbook have less material in the section “Classification of Energy” and only briefly cover it.

Among the six editions of the textbook, the Education Science edition and the Shanghai Science and Education edition set the example question of “Energy and sustainable development”, which is not covered in other editions. In terms of the number of example questions, the Shanghai Science and Education edition is more than the Education Science edition. As far as the sample question format is concerned, the Shanghai Science and Education edition uses simple and concise language to describe, and the complete solution is the main; The Education Science edition includes questions, analysis, answers and expansion, and each module is more detailed [8] . The specific comparison is shown in Table 3.

The table above illustrates how the example problems in the two versions of the textbook differ significantly from one another. One difference is the variation in the number of sample problems. The first section of the Education Science version contains just one sample problem. The second and fourth parts of the Shanghai Science and Education edition contain two sample problems. The application of the energy conservation law is the main focus of the Education Science edition’s content. The Shanghai Science and Education edition focuses on the effects of energy usage on life and the environment.

On the other hand, there are differences in the format of example problems. The Education Science edition of the sample problems section, for example, demonstration, presents a clear hierarchy, including questions, analysis, answers and extension of several modules, each module is described in detail, and in the analyzing section, there is strong guidance for students, for example, it seems to be easy to explain in terms of conservation of energy. In the expansion section, the education on the history of the science of perpetual motion machines is permeated, which plays an important role in developing students’ scientific literacy [9] . The Shanghai Science and Education edition also focuses on the process of answering questions, but its language is concise and condensed, and it shows more flexibility in the format, for example, the individual sample questions have added the thinking section, which can further disperse students’ thinking.

Statistics on the exercises of the six versions of the textbook “Energy and Sustainable Development” show that there are significant differences in the number and type of exercises and the examination of student’s abilities, as shown in Table 4.

As shown in Table 4, the Shanghai Science and Education edition and the Shanghai Science and Technology edition have the most exercises, both of which are 24 questions and rich in exercise types, with the Shanghai Science and Technology edition having a relatively single column of exercises, and the names of the section exercises and chapter exercises are all homework and activities. The People’s Education edition of the least number, does not involve the corresponding chapter exercises, types only thinking questions and calculation questions, focusing on the simple application of knowledge, more science and technology and production, and life in the background, for example: “Observe the household goods, point out what energy conversion? What is the maximum power generated by the Three Gorges Power Station?” These questions are easier to answer as long as students master the knowledge and think a little.

The Education Science edition of the exercises is arranged as 1 calculation question, 13 reflection questions, and section exercises presented in the form of “self-evaluation”. The title with a short description of the language, the difficulty

is low, and most of the questions can’t mobilize students’ thinking at a deeper level, for example: “Do you know what forms of energy are there? On what basis is energy categorized?” Such questions are designed to consolidate and review learning.

The exercises in the Luke edition are set up with a strong openness, mostly presented in the form of inquiry activities and practical investigations, which are conducive to enhancing students’ sense of active participation and deepening their understanding of the relationship between science, technology, society and the environment, e.g., “consulting the information to understand the historical prospects of human use of nuclear energy and the challenges it faces, learning about the advantages and disadvantages of different sources of energy for generating electricity through questionnaire surveys, and learning about the perpetual motion machine through the Internet and libraries”.

The Guangdong edition has fewer exercises, but the types of questions are more varied, and the examination of student knowledge and ability is more comprehensive. For example, the multiple-choice questions and table questions on energy source categorization adequately examine students’ memorization and understanding of basic knowledge. Reflective and calculating questions require students to apply what they have learned to some simple situations, which might help pupils develop their fundamental math and logical thinking skills. Practice and extension questions require students to comprehend and apply relevant knowledge through specific investigations or practices, which helps to build the link between physical knowledge and social reality.