  Electromagnetism (E&M) is often challenging for students enrolled in
introductory college-level physics courses. Compared to mechanics, the
mathematics of E&M is more sophisticated and the representations are more
abstract. Furthermore, students may lack productive intuitions they had with
force and motion. In this article, we explore the mathematization of electric
charge. Specifically, we explore how difficulties with positive and negative
signs can arise for learners who approach integers primarily as positions on a
number line.
