A double integrator is a dynamical model for a wide variety of physical systems. This includes a mass moving in one dimension and an object rotating around a shaft. It represents a broad class of systems with two states. In this chapter, you will learn how to model a double integrator and how to control it. In the process, you will create some very important functions for implementing control systems, plotting, and performing numerical integration. This will provide a springboard to other, more complex systems in later chapters.