Physics 9A and 9HA are the first of their respective sequences of introductory physics for engineers and scientists. Physics 9 is a four-course sequence that serves the vast majority of engineering and pure science majors. Physics 9H is a five-course series that provides a more rigorous and challenging treatment of introductory physics which typically attracts physics or applied physics majors, as well as a small number of the more ambitious engineering majors. Both sequences are calculus-based and carry with them high levels of mathematics prerequisites. The two sequences diverge after 9A/9HA, which cover classical mechanics.