What is the formula used to express pressure loss due to friction between the air and the pipe wall?

The correct answer is the Darcy Formula, which is specifically used to calculate pressure loss due to friction within a fluid moving through a pipe. This formula takes into account factors such as the fluid's viscosity, density, the diameter and length of the pipe, and the roughness of the pipe's interior surface. The primary use of this formula is in applications involving fluid dynamics in various piping systems, including plumbing.

The Darcy Formula is fundamentally important in the design of plumbing systems as it allows engineers and plumbers to predict how much pressure will be lost as water or air flows through pipes, which is crucial for ensuring adequate flow rates and system efficiency.

When comparing the other options, Pascal's Principle relates to the transmission of pressure in fluids but does not specifically address friction losses in pipes. The Bernoulli Equation provides a general relationship between pressure, velocity, and elevation in fluid flow but does not account for friction effects directly. The Poiseuille Equation applies to laminar flow in cylindrical pipes and focuses on viscous flow but is not as widely applicable for turbulent flows typically encountered in plumbing design.