This document defines key terms related to fluids and fluid dynamics. It describes the basic properties of fluids like pressure, temperature, viscosity, and density. It then discusses Poiseuille's law, which states that fluid flow through a tube is directly proportional to pressure difference and the fourth power of the radius, and inversely proportional to length and viscosity. The document applies Poiseuille's law to blood flow and other physiological contexts. It discusses how factors like radius, length, and viscosity impact resistance to fluid flow.