Fluidstatik

Fluidstatik, commonly called hydrostatics, is the branch of fluid mechanics that analyzes fluids at rest. It studies how pressure is distributed inside a stationary fluid, how pressure depends on depth, and the resultant forces on boundaries and submerged bodies. The standard framework assumes a continuous, incompressible fluid in a uniform gravitational field, with boundaries that may exert normal (perpendicular) pressures.

The central equation is the hydrostatic equilibrium: dP/dz = rho g, where P is pressure, z is vertical depth, rho is fluid density, and g is acceleration due to gravity. Integrating for a fluid with a free surface open to the atmosphere yields P = P_atm + rho g h, where h is the vertical depth below the free surface. The pressure at a point inside the fluid is isotropic and depends only on depth (if rho is constant).

Buoyancy: An object submerged in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid (Archimedes' principle). Floating and submerged states are determined by the relative densities (and the balance of forces). The concept underpins the stability of ships and submarines.

Common applications include barometry and manometry, calibration of measuring devices, analysis of water columns in pipes, dam and harbor design, and the study of atmospheric air columns in meteorology. Limitations include neglect of viscous stresses and dynamic effects; for gases, density may vary with height, requiring the hydrostatic equation to account for variable rho.