The pendulum was an important scientific instrument in the 17th century. It became a typical textbook problem in the 18th century. After the introduction of vectors in physics in the 1890s, the pendulum problem started to be progressively solved in the manner we know nowadays from introductory mechanics courses. Starting from "F = ma" and using the tangential component of weight, we arrive at the equation of motion. The other part of "F = ma," which concerns the weight radial component, tension and centripetal force, has in no way deserved the same attention from textbook writers, if any. Physics education research has, however, pointed out relevant aspects of the phenomenon related with the latter part of the equation. The present paper presents an experiment, which reflects those relevant aspects, and provides a mathematical insight into the phenomenon suitable for the high school student.