Hydrostatics is the branch offluid mechanics that studiesfluids athydrostatic equilibrium[1] and "the pressure in a fluid or exerted by a fluid on an immersed body".[2] The word "hydrostatics" is sometimes used to refer specifically to water and other liquids, but more often it includes both gases and liquids, whethercompressible orincompressible. It encompasses the study of the conditions under which fluids are at rest instable equilibrium. It is opposed tofluid dynamics, the study of fluids in motion.
Hydrostatics offers physical explanations for many phenomena of everyday life, such as whyatmospheric pressure changes withaltitude, why wood and oil float on water, and why the surface of still water is alwayslevel according to thecurvature of the earth.
Some principles of hydrostatics have been known in an empirical and intuitive sense since antiquity, by the builders of boats,cisterns,aqueducts andfountains.Archimedes is credited with the discovery ofArchimedes' Principle, which relates thebuoyancy force on an object that is submerged in a fluid to the weight of fluid displaced by the object. TheRoman engineerVitruvius warned readers aboutlead pipes bursting under hydrostatic pressure.[3]
The "fair cup" orPythagorean cup, which dates from about the 6th century BC, is a hydraulic technology whose invention is credited to the Greek mathematician and geometer Pythagoras. It was used as a learning tool.[citation needed]
The cup consists of a line carved into the interior of the cup, and a small vertical pipe in the center of the cup that leads to the bottom. The height of this pipe is the same as the line carved into the interior of the cup. The cup may be filled to the line without any fluid passing into the pipe in the center of the cup. However, when the amount of fluid exceeds this fill line, fluid will overflow into the pipe in the center of the cup. Due to the drag that molecules exert on one another, the cup will be emptied.
Heron's fountain is a device invented byHeron of Alexandria that consists of a jet of fluid being fed by a reservoir of fluid. The fountain is constructed in such a way that the height of the jet exceeds the height of the fluid in the reservoir, apparently in violation of principles of hydrostatic pressure. The device consisted of an opening and two containers arranged one above the other. The intermediate pot, which was sealed, was filled with fluid, and severalcannula (a small tube for transferring fluid between vessels) connecting the various vessels. Trapped air inside the vessels induces a jet of water out of a nozzle, emptying all water from the intermediate reservoir.[citation needed]
Pascal made contributions to developments in both hydrostatics and hydrodynamics.Pascal's law is a fundamental principle of fluid mechanics that states that any pressure applied to the surface of a fluid is transmitted uniformly throughout the fluid in all directions, in such a way that initial variations in pressure are not changed.
Liquids can havefree surfaces at which they interface with gases, or with avacuum. In general, the lack of the ability to sustain ashear stress entails that free surfaces rapidly adjust towards an equilibrium. However, on small length scales, there is an important balancing force fromsurface tension.
When liquids are constrained in vessels whose dimensions are small, compared to the relevant length scales,surface tension effects become important leading to the formation of ameniscus throughcapillary action. This capillary action has profound consequences for biological systems as it is part of one of the two driving mechanisms of the flow of water inplantxylem, thetranspirational pull.
Without surface tension,drops would not be able to form. The dimensions and stability of drops are determined by surface tension. The drop's surface tension is directly proportional to the cohesion property of the fluid.
^"Hydrostatics".Merriam-Webster. Retrieved11 September 2018.
^Marcus Vitruvius Pollio (ca. 15 BCE),"The Ten Books of Architecture", Book VIII, Chapter 6. At the University of Chicago's Penelope site. Accessed on 2013-02-25.
