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Overview
Fluid mechanics is the study of fluids, meaning liquids and gases. It includes fluids at rest, fluids in motion, pressure, density, buoyancy, viscosity, flow rate, turbulence, and forces produced by fluids. Fluid mechanics is essential for understanding air, water, blood, fuel, weather, aircraft, ships, pipes, pumps, and natural flows.
What Is a Fluid?
A fluid is a substance that can flow and take the shape of its container. Liquids and gases are fluids because they deform continuously under applied shear stress.
Fluid Statics
Fluid statics studies fluids at rest. It includes pressure with depth, buoyancy, Pascal's principle, and forces on submerged surfaces.
Fluid Dynamics
Fluid dynamics studies fluids in motion. It includes flow speed, flow rate, streamlines, viscosity, turbulence, and pressure changes.
Pressure and Density
Pressure and density are central fluid properties. Pressure describes force per area, while density describes mass per volume.
Viscosity
Viscosity is a fluid's resistance to flow. Honey has higher viscosity than water. Air has lower viscosity than many liquids but still produces drag.
Laminar and Turbulent Flow
Laminar flow is smooth and organized. Turbulent flow is irregular, swirling, and chaotic. Many real flows transition between these regimes.
Applications
Fluid mechanics is used in plumbing, aviation, medicine, meteorology, oceanography, engines, pumps, turbines, ventilation, and environmental science.
Common Mistakes
A common mistake is thinking fluids are only liquids. Gases are also fluids and obey many of the same broad principles.
Why This Matters in Physics
Fluid mechanics connects mechanics, thermodynamics, engineering, weather, biology, transportation, and environmental systems.