The famous French philosopher, mathematician and physicist of the 17th century Blaise Pascal made an important contribution to the development of modern science. One of his main achievements was the formulation of the so-called Pascal's law, which is associated with the property of fluid substances and the pressure created by them. Let's take a closer look at this law.
Scientist's short biography
Blaise Pascal was born on June 19, 1623 in Clermont-Ferrand, France. His father was a vice president of tax collection and a mathematician, and his mother belonged to the bourgeois class. From a young age, Pascal began to show interest in mathematics, physics, literature, languages, and religious teachings. He invented a mechanical calculator that could perform addition and subtraction. He spent a lot of time studying the physical properties of fluid bodies, as well as developing the concepts of pressure and vacuum. One of the important discoveries of the scientist was the principle that bears his name - Pascal's law. Blaise Pascal died in 1662 in Paris due to paralysis of the legs - an illness thatwho accompanied him from 1646.
Pressure concept
Before considering Pascal's law, let's deal with such a physical quantity as pressure. It is a scalar physical quantity denoting the force that acts on a given surface. When a force F begins to act on a surface of area A perpendicular to it, then the pressure P is calculated using the following formula: P=F / A. The pressure is measured in the International System of Units SI in pascals (1 Pa=1 N/m2), that is, in honor of Blaise Pascal, who devoted many of his works to the issue of pressure.
If the force F acts on a given surface A not perpendicularly, but at some angle α to it, then the expression for pressure will take the form: P=Fsin(α)/A, in this case Fsin(α) is the perpendicular component of the force F to the surface A.
Pascal's law
In physics, this law can be formulated as follows:
Pressure applied to a practically incompressible fluid substance, which is in equilibrium in a vessel having non-deformable walls, is transmitted in all directions with the same intensity.
You can verify the correctness of this law as follows: you need to take a hollow sphere, make holes in it in various places, supply this sphere with a piston and fill it with water. Now, by applying pressure on the water with the piston, you can see how it pours out of all the holes at the same speed, which means that the water pressure in the area of \u200b\u200beach hole is the same.
Liquids and gases
Pascal's law is formulated for fluid substances. Liquids and gases fall under this concept. However, unlike gases, the molecules that form a liquid are located close to each other, which causes liquids to have such a property as incompressibility.
Due to the property of the incompressibility of a liquid, when a finite pressure is created in a certain volume of it, it is transmitted in all directions without loss of intensity. This is exactly what Pascal's principle is about, which is formulated not only for fluid, but also for incompressible substances.
Considering in this light the question of "gas pressure and Pascal's law," it should be said that gases, unlike liquids, are easily compressed without maintaining volume. This leads to the fact that when an external pressure is applied to a certain volume of gas, it is also transmitted in all directions and directions, but at the same time it loses intensity, and its loss will be the stronger, the lower the density of the gas.
Thus, Pascal's principle is valid only for liquid media.
Pascal principle and hydraulic machine
Pascal's principle is used in various hydraulic devices. In order to use Pascal's law in these devices, the following formula is valid: P=P0+ρgh, here P is the pressure that acts in the liquid at depth h, ρ - is the density of the liquid, P0 is the pressure applied to the surface of the liquid, g (9, 81m/s2) - free fall acceleration near the surface of our planet.
The principle of operation of a hydraulic machine is as follows: two cylinders that have different diameters are connected to each other. This complex vessel is filled with some liquid, such as oil or water. Each cylinder is provided with a piston so that no air remains between the cylinder and the surface of the liquid in the vessel.
Assume that a certain force F1 acts on a piston in a cylinder with a smaller section, then it creates pressure P1 =F 1/A1. According to Pascal's law, the pressure P1 will instantly be transferred to all points of space inside the liquid in accordance with the above formula. As a result, the pressure P1 with the force F2=P1 A2=F1A2/A1. The force F2 will be directed opposite to the force F1, that is, it will tend to push the piston up, while it will be greater than the force F1 exactly as many times as the cross-sectional area of the machine's cylinders differs.
Thus, Pascal's law allows you to lift large loads with small balancing forces, which is a kind of Archimedes' lever.
Other applications of Pascal's principle
The considered law is used not only in hydraulic machines, but findswider application. Below are examples of systems and devices whose operation would be impossible if Pascal's law was not valid:
- In the brake systems of cars and in the well-known anti-lock ABS system, which prevents the wheels of the car from blocking during braking, which helps to avoid skidding and slipping of the vehicle. In addition, the ABS system allows the driver to maintain control of the vehicle when the latter performs emergency braking.
- In any type of refrigerators and cooling systems where the working substance is a liquid substance (freon).
