What principle states that total energy content remains constant when fluid flows without a change in velocity?

Bernoulli's Principle articulates that in a steady, incompressible flow of fluid, the total mechanical energy of the fluid remains constant when there are no work interactions being performed on the system. This principle integrates the concepts of kinetic energy (associated with fluid velocity) and potential energy (due to fluid pressure), highlighting the relationship between these energies when fluid velocity remains unchanged.

In practical terms, Bernoulli's Principle describes how an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or potential energy within a confined system. This is fundamental in understanding various vascular dynamics, as it relates directly to blood flow and pressure in arteries.

Poiseuille's Principle, while relevant to flow behavior in a cylindrical tube, particularly emphasizes the relationship between pressure, flow rate, and viscosity, rather than the conservation of total energy. Pascal's Principle focuses on the transmission of pressure in incompressible fluids, while Newton's Laws primarily deal with forces and motion, not the specific conservation of energy in fluid dynamics. Therefore, the correct answer emphasizes the constancy of total energy in fluid flow as described by Bernoulli's Principle.