In support of efforts to foreground functions as central objects of study in algebra, this study provides evidence of how secondary students use trigonometric functions in contextual tasks. I examined secondary students' work on a problem involving modeling the periodic motion of a Ferris wheel through the use of a visual programming environment. Using the cK\¢ model of conceptions, I characterized 5 conceptions of sine and cosine functions in students' work that differed in the ways that students interpreted the given problem, their use of semiotic resources, and the control structures that motivated their work. This study illustrates the range of prior knowledge and resources that students may draw on in their use of trigonometric functions as well as how the goals of students' work inform their reasoning about trigonometric functions.