This concept module on time constants is one of thirteen modules that provide a flexible, laboratory-based physics instructional package designed to meet the specialized needs of students in two-year, postsecondary technical schools. Each of the thirteen concept modules discusses a single physics concept and how it is applied to each energy system. In this module, time constants are shown to be common to different energy systems and to serve, therefore, as a unifying concept. Included with the concept module are seven application modules that discuss a specific application of a single concept in a single energy system, and contain a student laboratory exercise. Laboratory modules included are Shock Isolation by Absorbers, Rate of Emptying Tanks, Resistance Capacitance Circuits, RL Circuits, Resistance Inductance Capacitance Circuits, Response Time of Thermocouples, and Time Constants of Heating and Cooling. (LRA)