The document discusses bicycles as a system composed of subsystems. It defines a system as a set of entities that interact with each other, and a subsystem as a set of elements that is itself a system and part of the whole. It prompts the reader to think about their experience with bicycles and how they work. It links to an article about the history and design of early bicycles. It asks the reader to identify bicycle parts and subsystems, and to choose one to research in more detail, answering questions about its function, how it affects the bicycle, and how understanding bicycle systems relates to understanding the human body.