More than ten years have passed since the publication of the first edition of this book .. Despite the fact that almost simultaneously there were several good books devoted to the same section of the course of general physics, our book found its readers. This is evidenced by the rapid disappearance of the book from the shelves of bookstores, not excluding bookish. Since then, the opinion of the authors about what should be the course of molecular physics in high school has not undergone significant changes, but in this edition the book has been partially revised. some paragraphs are rewritten, some others are reordered, new paragraphs are introduced. These changes are partly due to the experience of "exploitation" of the book, partly - changes that occur over time in physics itself. The general nature of the book, however, has not changed. The authors hope that the reworking of the book led to its improvement.