Author: Brigitte Servatius
Reference: Newsletter of the SIAM Activity Group on Discrete Math. 4, (1), 1--5, 1993.
Abstract: A wide variety of physical structures, e.g. scaffolding (rigid), or a DNA molecule (non-rigid), may be modeled as a collection of rigid rods connected to one another by idealized ball joints. By a ball joint we mean a connection between a collection of rods which imposes the sole restriction that they share common endpoint. For a given structure, the basic question that arises is whether it is rigid and, if not, how to describe its motion. We would like to describe some of the applications of combinatorics to this area.
An illustration of an infinitesimal motion of a graph in the plane.