An introduction to physics, written to be challenging, surprising and motivating on each of its pages. How do colours appear? How do muscles work? What is the maximum force found in nature? What do love, fireworks and butterflies have in common? Is levitation possible? What does 'quantum' mean? Is time travel possible? Is the universe a set? Which problems in physics are still open? Exploring these questions with this text will provide at least as much pleasure as making love. This free textbook presents the science of motion: physics. The book is written for curious men, women, boys and girls: it is entertaining, surprising and challenging on every page. With little mathematics, starting from observations of everyday life, the text presents the most fascinating aspects of things that move. It explores mechanics, thermodynamics, special and general relativity, electrodynamics, quantum theory and modern attempts at unification. The essence of these fields is summarized in the most simple terms possible. For example, the text presents modern physics as consequence of the notions of minimum entropy, maximum speed, maximum force, minimum change of charge and minimum action. For each field of physics, the text presents the latest research results, the best animations, the best images, the most interesting physical puzzles and the most telling physical curiosities. It includes more than 600 animations, films and illustrations, more than 100 tables, more than 1700 challenges and puzzles, and includes over 900 internet links.