This study investigates the predictive influences of achievement motivational variables that may sustain students' engagement in physics and influence their future enrolment plans in the subject. Unlike most studies attempting to address the decline of physics enrolments through capturing students' intention to enrol in physics before ever studying the subject, this study is novel because it captures the perceptions of students currently enrolled in senior secondary physics and their subsequent enrolment intentions after completing modules from the physics curriculum. Participants comprised of senior secondary students in year 11 completing their first year of physics in Australia across nine high schools in New South Wales. The Sustained Enrolment Models for Physics (SEMP), which drew upon the Expectancy-Value (EV) theoretical foundation, proposed predictive relations among students' achievement motivation, sustained engagement, and enrolment intentions in relation to physics. The data showed a good fit to the theoretically developed model for all four physics topics from the year 11 curriculum. The path coefficients of the models demonstrated the strength of relationships among the variables for each of the topics. The topic specificity of SEMPs allowed the mapping of students' motivational patterns at a more sensitive level than the domain-specific level and suggested that the relative influence of motivational precursors can vary by topic. This study advanced the EV research knowledge that, while values may be significant, it is the expectancies that largely predict students' sustained choice intentions in relation to physics. Implications for these findings are discussed.