The geometry of bar-and-joint machines

Tom Braden, Department of Mathematics and Statistics, U. Mass., Amherst

Abstract: I will talk about the motions of machines made up of rigid rods connected by ideal, infinitely flexible joints. The set of possible positions of such a machine can be considered as a geometric space called its configuration space. A continuous motion of the machine gives a path in the configuration space, for example. Trying to understand how the structure of the machine affects the geometry of the configuration space (Is it smooth? What is its dimension? How many "holes" does it have?) leads directly to some fundamental ideas from geometry: tangent spaces, critical points, and Morse theory.