Hydrostatic

Hydraulic and Hydrostatic Table, 1728 in Cyclopaedia, Volume 1.

Hydrostatics is the branch of hydraulics that studies the phenomena associated with fluids that are in a state of rest.

Fluid characteristics

Fluid is called that continuous medium formed by some substance between whose molecules there is only a weak force of attraction. The defining property is that fluids can change shape without the appearance of restorative forces tending to recover the "original" (which constitutes the main difference with a deformable solid, where there are restorative forces).

The liquid, gaseous and plasma states of matter are fluids, in addition to some that present characteristics of these, a phenomenon known as solifluxion and that present it, among others, glaciers and magma.

The main characteristics of all fluids are:

• Cohesion. Force that holds together the molecules of the same substance.
• Surface tension. Phenomenon that occurs due to the attraction between the molecules of the surface of a liquid.
• Accessibility. Attractive force manifested between the molecules of two different substances in contact.
• Capilarity. It occurs when there is contact between a liquid and a solid wall, due to the adhesion phenomenon. If the wall is a very thin container or tube (called "capills"), this phenomenon can be seen very clearly.

Pressure of a fluid in equilibrium

In terms of classical mechanics, the pressure of an incompressible fluid in a state of equilibrium can be expressed by the following formula:

δ δ P=ρ ρ gh{displaystyle delta P=rho gh}

where P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height.

Pascal's Principle

Height of a ton under pressure from a water column.

Pascal's principle is a law enunciated by the French physicist and mathematician Blaise Pascal (1623–1662) that is summarized in the phrase: «the increase in pressure applied to a surface of an incompressible fluid (usually it is an incompressible liquid), contained in a non-deformable container, is transmitted with the same value to each of its parts".

That is, if pressure is applied to a non-compressible liquid in a closed container, it is transmitted with equal intensity in all directions and senses. This type of phenomenon can be seen, for example, in the hydraulic press or in the hydraulic jack; both devices are based on this principle. The condition that the container is non-deformable is necessary so that changes in pressure do not act deforming the walls of the container instead of being transmitted to all points in the liquid.

Archimedes' Principle

Archimedes' principle states that any solid body that is totally or partially submerged in a fluid will be pushed upwards by a force equal to the weight of the liquid displaced by the solid body. The object does not necessarily have to be completely submerged in said fluid, since if the push it receives is greater than the apparent weight of the object, it will float and be only partially submerged.