Difference Between Fluid Dynamics and Fluid Mechanics

Fluid Dynamics vs Fluid Mechanics

Fluid dynamics and fluid mechanics are two very important fields of studies in physics. These fields are very important when it comes to subjects such as aeronautic engineering, nautical engineering, civil and military engineering, and various other fields. Fluid mechanics and fluid dynamics can be taken as a whole new field of classical mechanics where probability and thermodynamics play very important roles. In order to fully understand the aspects of fluid mechanics and fluid dynamics, one must have a good knowledge in energy conservation, vector fields, and even statistical thermodynamics. In this article, we are going to discuss what fluid mechanics and fluid dynamics are, their founding principles, similarities, applications, and finally their differences.

Fluid Mechanics

A fluid is defined as either a gas or a liquid. Fluid mechanics is the study of behavior of liquids and gasses. More properly defined fluid mechanics is the study of fluids and forces on them. Fluid mechanics has three main fields. They are namely fluid statics that studies the fluids at rest, fluid kinematics that studies the movements of fluids, and fluid dynamics that studies the effects of forces on fluid motion. But as we know, liquids and gasses don’t have a steady state. There is always a random motion due to the thermal agitation of gasses and liquids. However, the thermal agitation of gasses is higher than that of liquids. One of the founding fathers of fluid mechanics was Archimedes. His famous buoyancy principle was one of the very first principles in fluid mechanics. Later, prominent scientists like Leonardo da Vinci, Evangelista Torricelli, Isaac Newton, Blaise Pascal, Daniel Bernoulli and prominent mathematicians like Euler, d’Alembert, Lagrange, Poisson and Laplace made significant contribution to the study of fluid mechanics. The field of viscosity was later developed by Poiseuille, Hagen, Navier and Stokes.

Fluid Dynamics

Fluid dynamics is a sub field of fluid mechanics. Fluid dynamics studies the effect of forces on fluid motion. Most notable equations in fluid dynamics are Bernoulli’s equation, which was proposed by Daniel Bernoulli. It is defined for an incompressible, inviscid fluid on a steady and non-turbulent flow. For such a fluid, the summation of the hydrostatic pressure, the kinetic energy per unit volume and the potential energy per unit volume is a constant. This can be applied to any arbitrary line of flow in the fluid. However, fluids in real don’t obey this equation since they are compressible and viscous. Other important equations of fluid dynamics are Navier-Stokes equations and Reynolds transport theorem. These are basically mass conservation, energy conservation and momentum conservation in different forms. An important aspect of fluid dynamics is aerodynamics. Airplanes use the Bernoulli theorem to create a pressure difference between upside and downside of the wings. This makes the flying possible. Hydrodynamics also plays an important part in day to day life.