Fluid

The liquids and the gases are designated indistinctly with the name of fluid, although notable differences between one exist and other, which they are explained by means of the method corpuscular, for the grade of freedom, with which there can move his molecules, the interesting thing that also present common characteristics: first of all we have, because he lacks proper form, other one the one that they exercise and the directions can transmit pressures in everything. A fluid at rest practises and transmits to his mass and to the walls of the receptacle that contains it for giving an example, to explain the study of the fluids at rest they receive the name of hydrostatics.

The raw material, it appears in the nature in four physical states: solid, liquid, gaseous, and plasma, the particles that form a body in been solid, occupy fixed positions, size and form defined. The liquid and gaseous states do not have fixed form, but they acquire that of the receptacle, which contains them; his particles it can flow, that's why it is called a fluid, as soon as the plasma is constituted by a fluid obtained by means of the finished ionization of a gas, initially neutral, to very high temperatures: his location cannot be realized, with conventional receptacles, but it needs the contests of magnetic fields.

Statics of fluids.
In contrast to the gases, the liquids possess form own in his surfaces free, that in general, it is flat and horizontal bowing lightly in the outskirts of the walls of the receptacle that contains it, forming a hollow or convex meniscus, according to the nature of the liquid and of the material that it constitutes where it is contained, the volume of the liquids changes little with the conditions of pressure and temperature, from what it is said, that they are uncompressible. The gases, due to the big mobility, which has his molecules, are expansibles.

Pressure hydrostatics.
Departing from the pressure as the force, which acts on the surface unit, N/m measures himself ², unit of pascal, where the pressure that exists in the any point of the interior of a liquid, stems from the weight of the liquid, which exists over him. The value of the pressure hydrostatics in a point can be multiplying the distance, that there are even the surfaces well be his depth.

Absolute specific gravity.
In the study of the pressures that exercise the fluids at rest it is necessary to know the thickness or the absolute specific gravity of the fluid, next we have the following relation:
d = m/v; where m is equal to the mass of the substance, v to the volume that it occupies, d the thickness.
But the weight of the substance is (m) (g) = P, where g is the gravity, d.g is considered following = m.g/V, replacing the relation of the weight we have left:
d.g = P/V.

In terms physicist, the absolute specific gravity of a substance, represents the weight of the unit.

If p1 and p2, they are the pressures in two points of a fluid mass at rest, of specific gravity in P and the distance vertica, that it separates to the above mentioned points is h, it is fulfilled that p2-p1 = P.h. (Image prepared for @coolxxx)

We have the following exercise.
A cylindrical receptacle of radio R = 8cm, contains glycerin of absolute specific gravity p = 1,32/cm ³, up to a height h = 40 cm. What the weight of the glycerin will be in kp.

Information.
R = 8 cm
h = 40 cm
p = 1,32/cm ³
P =?

Solution.
P = p.v
V = base x height
V = pi. R ². h = 3,14 x 64 cm ² x 40 cm
V = 8038,4 cm ³

P = 1,32 p/cm ³ x 8038,4 cm ³
P = 10610,688 p = 10610,688 kp
P = 10610,688 kp

Beginning of pascal.
To explain it, let's consider a point A, in the free surface of a liquid at rest and another point b, in the bosom of the liquid, separated from the first one for the vertical distance h.

Pn = pA p.h, in such a way that it operates on the sucker with a such force that the pressure in A, it is pA p, it is necessary, so that the equation does not alter, the pressure in B, is pn p, this result knows each other with the name of the beginning of pascal and is enunciated of the following way:

Any change of pressure, in a point of a mass flown in balance, is transmitted íntegramente to all the other points, from the fluid mass and to the walls of the receptacle that contains it.

If the pressure in a point A of a fluid mass, at rest increases in quantity p, deacuerdo with the general equation of the hydrostatics, it will be had that the pressure in a point B, placed to the depth h, increases the same quantity p, this result is known by the name of beginning of Pascal. (image prepared for @coolxxx)

The beginning of Arquímedes.
An object immersed in a fluid is submitted to a force of direction vertical and felt up, called propulsion, which magnitude is equivalent to the weight of the displaced fluid. An immediate consequence of this floating beginning of the bodies, which can express to themselves if an object floats in a liquid, the weight of the object is equal to the propulsion, which exercises the liquid on the submerged portion of the object.

An object immersed in a fluid is submitted, to a force of direction vertical and felt up, call propulsion, which magnitude is equivalent to the weight of the displaced fluid. (Image prepared for @coolxxx)

Atmospheric pressure.
The ground is surrounded by the ambience, which is a gaseous layer constituted by a gas miscellany, the weight of these gases constitutes the atmospheric pressure, which measures with a few devices so-called barometers, since in the ambience, it is the meteorological stage of the phenomena, factors that determine the atmospheric time they are the temperature, the humid one and the processes adiabáticos, that are the processes that are carried out without heat exchange from the exterior system.

We have the following scheme of a manometer of liquids, if the atmospheric pressure is po, the specific gravity of the liquid P and the difference between two branches of the pipe h, it is fulfilled that the pressure of the gas or steam shut up in the cylinder is p = po P.h. (Image prepared for @coolxxx)

Paradox hydrostatics.
This paradox alludes in case, where several receptacles of different forms and capacity, which funds have the same areas, where the force, which a liquid exercises on the fund of the receptacle, which contains it is independent from the form and capacity of the receptacle, being equivalent to the weight of the column it liquidates, that it takes the fund of the receptacle as a base and for height the distance between the fund and the level frees of the liquid.

The force that receptacles exercise the liquid on the fund of these cuatros, depends neither on the form of the receptacle nor of his capacity, to depend exclusively goes. of the area in S of the fund, of the height h between the fund and the free level of the liquid and of the specific gravity of this one. (Image prepared for @coolxxx)

Finally I think them following, thanks to the study of the mechanics of the fluid, between others are applied very much in the fields of the oceanography for the naval constructions.

In the automotive industry, the beginning of the fluid is applied, so much in the direction, the brakes, to guarantee more safety and better mechanical functionality, in the optimalización of the use of hydrocarbons.

Also we have it in: the hydraulic press, the cat, the brake, the elevator and the crane.

The beginning of Arquímedes is important in field of the statics of fluids, in the naval navigation and the manufacture of vessels.

Bibliographical consulted references.

WHITE, F. “ Mechanics of fluids ' Ed. McGraw Hill (2008).

CURL, A. “ Mechanics of fluids ” Ed. Thomson (2006).

POTTER RIPOLL, A., PÉREZ-SABORID SÁNCHEZ-SHEPHERD, M. " Essentials and applications of the Mechanics of Fluids " Ed. McGraw Hill (2005).

LÓPEZ-HERRERA SÁNCHEZ, J. M., SHOD GUTIÉRREZ, M. A., PÉREZ-SABORID SANCHEZ-SHEPHERD, M., POTTER RIPOLL, A. “ Mechanics of fluids: decisive problems ” Ed. McGraw Hill (2005).

ROCK VILA, R. “ Introduction to the Mechanics of the fluids ' Ed. Limusa (1980).

Bauman R. P., Schwaneberg R. Interpretation of Bernoullís Equation. The Physics Teacher, V-32, November 1994, pp. 478-488.

Bauman R. P: An alternative derivation of Bernoullís principle. Am. J. Phys. 68 (3) March 2000, p. 288-289

Behroozi F., Lambert B. To simple problem in hydrodynamics with to surprising solution. The Physics Teacher Vol 35, May, 1997, pp. 318-319

Behroozi F., Mohazzabi P., McCrickard J. P., Remarkable shapes of to catenary under the effect of gravity and surface tension. Am. J. Phys. 62 (12) December 1994, pp. 1121-1128

Berridge H J J. Radioactive decay chains - to digitalis method. Physics Education. September 1975, pp. 437-438