Students' difficulties with tension in massless strings. Part I

Many students enrolled in the introductory mechanics courses have learning difficulties related to the concept of force in the context of tension in massless strings. One of the potential causes could be a lack of functional understanding through a traditional instruction. In this article, we show a collection of this kind of students' difficulties at the New Mexico State University, at the Arizona State University, and at the Independent university of Ciudad Juarez in Mexico. These difficulties were collected during an investigation conducted not only in lab sessions but also in lecture sessions. The first part of the investigation is developed in the contexts of proximity and the length of strings.