At some point in their careers, most physicists make an attempt to read and understand Newton's Principia. Unfortunately, it is an extremely difficult book — it quickly becomes clear that one does not simply "read" the Principia. Even for a professional physicist, Newton's prose (written in Latin and translated to English) is difficult to follow. His diagrams and figures are complicated and confusing. To understand fully what Newton had done, the problems he posed would have to be solved by the reader.Newton's geometric methods and techniques, and the geometry and vocabulary that passed for common knowledge in the late 17th century, are now arcane and all but inaccessible to a modern reader. The contents of the Principia are not. Most physicists and physics students, and many scientists in general, would find the physics in the Principia interesting, illuminating, and useful.This book presents all the wonderful physics in the Principia in a manner that a modern reader can recognize and understand, using physics and mathematics as we understand them in the 21st century.