Newton's cradle: a smartphone-based video analysis approach

In this paper we discuss a simple and inexpensive method to study pendular movement and head-on elastic collisions, according to the Bring-Your-Own-Device philosophy. A popular toy, the Newton's cradle, can be used to provide a pendular or a collision system, and the movements of the spheres can be tracked by video analysis, using a smartphone. We show that the conservation of momentum and kinetic energy, upon collision of two or more spheres, can be easily confirmed and that the pendular movement can be studied in detail. A more complete analysis, appropriate for undergraduate students in STEM degrees, is also suggested.