Physics. Grade 9 A Textbook for educational institutions - 5 th ed., Revised - ("Academic school textbook") (GRIF) / Fizika. 9 klass Uchebnik dlya obshcheobrazovatelnykh uchrezhdeniy - 5-e izd.,pererab - ("Akademicheskiy shkolnyy uchebnik") (GRIF)