Hydrostatic equilibrium

The hydrostatic equilibrium ( hydro " water " static " unmoved ") is a balance between gravity, which pulls a solid body down, and the static lift, trying to lift the body from the liquid upwards.

More generally, the hydrostatic equilibrium is always the balancing of a directed force and a pressure gradient. Then also convection over hydrostatic balance can be described.

Biology

All living things with air pockets in the body ( which applies to virtually all bony fish ) have to readjust constantly to maintain hydrostatic equilibrium. As the pressure increases with depth, trapped air is compressed to the same degree, as the pressure increases. Compression reduces the volume and therefore buoyancy. The hydrostatic equilibrium is always so for a predetermined depth, and must be adjusted when changing the depth. Creatures with air pockets in the body are fish with their swim bladder and humans ( divers) with their lungs or diving equipment. When divers are called tare this readjustment.

Mechanics

Diving boats ( submarines) can absorb water by flooding of dip tanks and dive so by increasing their ( average ) density of surface running. By blowing -dose ( with compressed air) such ( rigid ) tanks can be controlled their water content and the submarine be adjusted moderately dense to the surrounding water.

A diver fills the soft, flaccid bladder his buoyancy compensator ( BC ) with air to that extent that it - allowed tared hovering without strenuous swimming motion at a certain depth - with average lung filling.

The thus achieved hydrostatic equilibrium is only unstable. Something deeper dive compresses both the air bubble in the diver vest ( and additionally in neoprene ( foam) indicate ) and the volume of air in an unpressurized ( open at the bottom ) immersion tank. The gravitational force is greater than the buoyant force and pulls boat or man down further, if left unchecked by blowing air into tank or bladder. Conversely, the prospecting of a higher dive location a part of the expanded air then be discharged from the bladder. Finding this balance is trained as a tare.

The Galileo thermometer float depending on the temperature (and therefore density) different balls.

Astrophysics

For larger celestial bodies such as ( dwarf ) planets or stars, there is a stratification, which is caused by materials of different density. This arises for each layer boundary a balance between the attractiveness of underlying mass and the pressure generated by various physical processes, so that a spherical shape or such as in the case of the earth in the form of an inner sphere ( the made ​​of iron and nickel core of the Earth ) and overlying spherical shells ( mantle and crust ) results. The pressure can be applied by the gas pressure as well as by the radiation pressure in stars or by the degeneracy pressure in white dwarfs or neutron stars.

Meteorology

In meteorology and atmospheric physics one uses the concept of air packet ( Parcel method), which is sufficiently homogeneous to be treated like a solid body in the atmosphere ( "float "). This hydrostatic equilibrium describes the Static stability ( stratification stability ) of the atmosphere.