Students of physics, even at the undergraduate level, often perceive common sense and the use of mathematical formalisms in problem solving as disconnected activities. We present an ethnographic account of a case study, a year-long research apprenticeship of an 11th grade physics student. The analysis examined the development of the student's understanding a mathematical equation as a model for a physical phenomenon, his use of that mathematization as a tool and as an object for sense making, and how these were nurtured by the mentor. Our analysis suggests that this process can be paralleled to the development of reading comprehension and that it involves the deciphering of the explicit and implicit meaning of the equation. We also show that using physics equations in this manner is not intuitive, and requires an epistemological change that needs to be necessitated for students.