2 - Pressure and flow

Abstract

This chapter presents the various terms and definitions used in hydraulics, the significance of Pascal's law and its applications, and the importance of flow and pressure in hydraulics. Pressure along with flow is one of the key parameters involved in the study of hydraulics. Pressure in a hydraulic system comes from resistance to flow. Fluids are composed of molecules that are in continuous random motion. These molecules move throughout the volume of the fluid colliding with each other and with the walls of the container as a result of which the molecules undergo a change in momentum. The chapter considers a surface within the fluid that is impacted by a large number of molecules. This results in a transfer in momentum from the molecules to the surface. The change in momentum transferred per second by these molecules on the surface gives the average force on the surface. The normal force exerted by the fluid per unit area of the surface is known as fluid pressure. Pascal's law states that the pressure applied to a confined fluid is transmitted undiminished in all directions. This law forms the basis for understanding the relationship among force, pressure, and area. The chapter studies two basic applications of Pascal's law; the hydraulic jack and the air-to-hydraulic booster. The chapter also discusses the study of liquids in motion under two headings; Hydrokinetics and Hydrodynamics.