Pascal's law of pressure was discovered in the 17th century by the French scientist Blaise Pascal, after whom it received its name. The formulation of this law, its meaning and application in everyday life are discussed in detail in this article.
The essence of Pascal's law
Pascal's law - the pressure that is exerted on a liquid or gas is transmitted to every point of the liquid or gas without changes. That is, pressure transfer occurs equally in all directions.
This law is valid only for liquids and gases. The fact is that the molecules of liquid and gaseous substances under pressure behave completely differently from the molecules of solids. Their movement is different from each other. If the molecules of liquid and gas move relatively freely, then the molecules of solids do not have such freedom. They only oscillate slightly, deviating slightly from their original position. And due to the relatively free movement of gas and liquid molecules, they exert pressure in all directions.
Formula and basic value of Pascal's law
The main quantity in Pascal's law is pressure. It is measured in Pascals (Pa). Pressure (P)– attitude strength (F), which acts on the surface perpendicular to its area (S). Hence: P=F/S.
Features of gas and liquid pressure
Being in a closed vessel, the smallest particles of liquids and gases - molecules - hit the walls of the vessel. Since these particles are mobile, they are able to move from a place with higher pressure to a place with low pressure, i.e. within a short time it becomes uniform over the entire surface of the occupied vessel.
To better understand the law, you can conduct an experiment. Let's take a balloon and fill it with water. Then we make several holes with a thin needle. The result will not be long in coming. Water will begin to flow out of the holes, and if the ball is compressed (i.e., pressure is applied), then the pressure of each jet will increase several times, regardless of the exact point at which the pressure was applied.
The same experiment can be done with Pascal's ball. It is a round ball with existing holes with a piston attached to it.
Rice. 1. Blaise Pascal
The fluid pressure at the bottom of the vessel is determined using the formula:
p=P/S=gpSh/s
p=gρ h
- g- acceleration of gravity,
- ρ – liquid density (kg/cub.m)
- h– depth (height of the liquid column)
- p– pressure in pascals.
Underwater, pressure depends only on the depth and density of the liquid. That is, in the sea or ocean the density will be greater with greater immersion.
Rice. 2. Pressure at different depths
Application of the law in practice
Many laws of physics, including Pascal's law, are applied in practice. For example, an ordinary water supply system could not function if this law were not in effect. After all, the water molecules in the pipe move chaotically and relatively freely, which means the pressure exerted on the walls of the water pipe is the same everywhere. The operation of a hydraulic press is also based on the laws of motion and equilibrium of fluids. The press consists of two interconnected cylinders with pistons. The space under the pistons is filled with oil. If a smaller piston with area S 2 is acted upon by a force F 2 , then a larger piston with an area S 1 is acted upon by a force F 1 .
Rice. 3. Hydraulic press
You can also experiment with raw and boiled eggs. If you pierce one and then the other with a sharp object, for example a long nail, the result will be different. A hard-boiled egg will go right through the nail, but a raw egg will shatter into pieces, since Pascal’s law will apply to a raw egg, but not to a hard-boiled one.
Pascal's law states that the pressure at all points of a fluid at rest is the same, that is: F 1 /S 1 =F 2 /S 2, whence F 2 /F 1 =S 2 /S 1.
The force F 2 is the same number of times greater than the force F 1, how many times the area of the larger piston is greater than the area of the small one.
What have we learned?
The main quantity of Pascal's law, which is studied in grade 7, is pressure, which is measured in Pascals. Unlike solids, gaseous and liquid substances exert equal pressure on the walls of the vessel in which they are located. The reason for this is molecules that move freely and chaotically in different directions.
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Pascal's law - The pressure exerted on a liquid (gas) in any one place on its boundary, for example, by a piston, is transmitted without change to all points of the liquid (gas).
But it is usually used like this:
Let's talk a little about Pascal's Law:
Each particle of liquid located in the gravitational field of the Earth is affected by the force of gravity. Under the influence of this force, each layer of liquid presses on the layers located underneath it. As a result, the pressure inside the liquid is at different levels will not the same. Therefore, in liquids there is pressure due to its weight.
From this we can conclude: The deeper we dive under water, the stronger the water pressure will act on us
The pressure due to the weight of the liquid is called hydrostatic pressure.
Graphically, the dependence of pressure on the depth of immersion in liquid is shown in the figure.
Based Pascal's law Various hydraulic devices operate: brake systems, presses, pumps, pumps, etc.
Pascal's law not applicable in the case of a moving liquid (gas), as well as in the case when the liquid (gas) is in a gravitational field; Thus, it is known that atmospheric and hydrostatic pressure decreases with altitude.
In the Formula we used:
Pressure
Ambient pressure
Pascal's law
Corollary of Pascal's law
Pascal's law is formulated as follows:
It should be noted that Pascal’s law is not about pressures at different points, but about disturbances pressure, therefore the law is also valid for liquid in the field of gravity. When moving incompressible fluid, we can conditionally speak of the validity of Pascal’s law, because adding an arbitrary constant value to the pressure does not change the form of the equation of motion of the fluid (Euler’s equation or, if the action of viscosity is taken into account, the Navier-Stokes equation), however in this case the term Pascal's law as a rule not applied. For compressible liquids (gases), Pascal's law, generally speaking, is not valid.
Various hydraulic devices operate on the basis of Pascal’s law: brake systems, hydraulic presses, etc.
see also
Notes
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See what "Pascal's Law" is in other dictionaries:
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- Participant: Kolesnikov Maxim Igorevich
- Head: Shcherbinina Galina Gennadievna
Introduction
Pascal's law became known in 1663. It was this discovery that formed the basis for the creation of superpresses with a pressure of over 750,000 kPa, a hydraulic drive, which in turn led to the emergence of hydraulic automation that controls modern jetliners, spaceships, numerically controlled machines, powerful dump trucks, mining combines, presses, and excavators. .. Thus, Pascal's law has found great application in the modern world. However, all these mechanisms are quite complex and cumbersome, so I wanted to create devices based on Pascal’s law in order to convince myself and convince my classmates, many of whom believe that it is stupid to waste time on “antiquity” when we are surrounded by modern devices that this topic is still interesting and relevant. In addition, devices created by oneself, as a rule, arouse interest, make one think, fantasize, and even look at the discoveries of “deep antiquity” with different eyes.
Object My research is Pascal's law.
Goal of the work: experimental confirmation of Pascal's law.
Hypothesis: knowledge of Pascal's law can be useful for designing construction equipment.
Practical significance of the work: My work presents experiments for demonstration in physics lessons in the 7th grade of a secondary school. The developed experiments can be demonstrated both in class when studying phenomena (I hope that this will help form some concepts when studying physics), and as homework for students.
The proposed installations are universal; one installation can be used to demonstrate several experiments.
Chapter 1. All our dignity is in the ability to think
Blaise Pascal (1623-1662) – French mathematician, mechanic, physicist, writer and philosopher. A classic of French literature, one of the founders of mathematical analysis, probability theory and projective geometry, creator of the first examples of computing technology, author of the basic law of hydrostatics. Pascal entered the history of physics by establishing the fundamental law of hydrostatics and confirmed Toricelli’s assumption about the existence of atmospheric pressure. The SI unit of pressure is named after Pascal. Pascal's law states that the pressure exerted on a liquid or gas is transmitted to any point without change in all directions. Even the famous Archimedes' law is a special case of Pascal's law.
Pascal's law can be explained using the properties of liquids and gases, namely: molecules of liquid and gas, hitting the walls of a container, create pressure. Pressure increases (decreases) with increasing (decreasing) concentration of molecules.
There is a widespread problem that can be used to understand the operation of Pascal's law: when fired from a rifle, a hole is formed in a boiled egg, since the pressure in this egg is transmitted only in the direction of its movement. A raw egg breaks into pieces, since the pressure of a bullet in a liquid, according to Pascal's law, is transmitted equally in all directions.
By the way, it is known that Pascal himself, using the law he discovered, in the course of his experiments, invented a syringe and a hydraulic press.
Practical significance of Pascal's law
The operation of many mechanisms is based on Pascal's law; otherwise, such properties of gas as compressibility and the ability to transmit pressure equally in all directions have found wide application in the design of various technical devices.
- Thus, compressed air is used in a submarine to lift it from depth. When diving, special tanks inside the submarine are filled with water. The weight of the boat increases and it sinks. To lift the boat, compressed air is pumped into these tanks, which displaces the water. The weight of the boat decreases and it floats up.
Fig.1. Submarine on the surface: the main ballast tanks (CBT) are not filled
Fig.2. Submarine in a submerged position: the Central City Hospital was filled with water
- Devices that use compressed air are called pneumatic. These include, for example, a jackhammer, which is used to open asphalt, loosen frozen soil, and crush rocks. Under the influence of compressed air, the peak of a jackhammer makes 1000-1500 blows per minute of great destructive force.
- In production, a pneumatic hammer and a pneumatic press are used for forging and processing metals.
- Air brakes are used in trucks and railway vehicles. In subway cars, doors are opened and closed using compressed air. The use of air systems in transport is due to the fact that even if air leaks from the system, it will be replenished due to the operation of the compressor and the system will function properly.
- The operation of an excavator is also based on Pascal's law, where hydraulic cylinders are used to drive its booms and bucket.
Chapter 2. The soul of science is the practical application of its discoveries
Experiment 1 (video, method of modeling the operating principle of this device at the presentation)
The action of Pascal's law can be observed in the operation of a laboratory hydraulic press, consisting of two connected left and right cylinders, uniformly filled with liquid (water). The plugs (weights) indicating the fluid level in these cylinders are highlighted in black.
Rice. 3 Diagram of a hydraulic press
Rice. 4. Application of hydraulic press
What happened here? We pressed down on the plug in the left cylinder, which forced the fluid out of this cylinder towards the right cylinder, as a result of which the plug in the right cylinder, experiencing fluid pressure from below, rose. Thus, the fluid transmitted pressure.
I conducted the same experiment, only in a slightly different form, at home: a demonstration of an experiment with two cylinders connected to each other - medical syringes connected to each other and filled with liquid-water.
The design and principle of operation of a hydraulic press is described in a 7th grade textbook for secondary schools,
Experiment 2 (video, using the modeling method to demonstrate the assembly of this device at a presentation)
In development of the previous experiment, to demonstrate Pascal’s law, I also assembled a model of a wooden mini-excavator, the basis of which is piston cylinders filled with water. Interestingly, as pistons that raise and lower the boom and bucket of the excavator, I used medical syringes invented by Blaise Pascal himself to confirm his law.
So, the system consists of ordinary medical syringes of 20 ml (function of control levers) and the same syringes of 5 ml (function of pistons). I filled these syringes with liquid – water. A dropper system was used to connect the syringes (provides sealing).
In order for this system to work, we press the lever in one place, the water pressure is transmitted to the piston, to the plug, the plug rises - the excavator begins to move, the excavator boom and bucket are lowered and raised.
This experiment can be demonstrated by answering the question after § 36, page 87 of A.V. Peryshkin’s textbook for 7th grade: “What experience can be used to show the peculiarity of the transmission of pressure by liquids and gases?” The experiment is also interesting from the point of view of the availability of the materials used and practical application of Pascal's law.
Experience 3 (video)
Let's attach a hollow ball (pipette) with many small holes to the tube with a piston (syringe).
Fill the balloon with water and press the plunger. The pressure in the tube will increase, water will begin to pour out through all the holes, and the water pressure in all streams of water will be the same.
The same result can be obtained if you use smoke instead of water.
This experiment is a classic demonstration of Pascal's law, but the use of materials available to each student makes it especially effective and memorable.
A similar experience is described and commented on in a 7th grade textbook for secondary schools,
Conclusion
In preparation for the competition, I:
- studied theoretical material on the topic I chose;
- created home-made devices and conducted an experimental test of Pascal's law on the following models: a model of a hydraulic press, a model of an excavator.
conclusions
Pascal's law, discovered in the 17th century, is relevant and widely used in our time in the design of technical devices and mechanisms that facilitate human work.
I hope that the installations I have collected will be of interest to my friends and classmates and will help me better understand the laws of physics.
The nature of the pressure of a liquid, gas and solid is different. Although the pressures of liquids and gases are of different natures, their pressures have one similar effect that differentiates them from solids. This effect, or rather a physical phenomenon, describes Pascal's law.
Pascal's law The pressure produced by external forces at some point in a liquid or gas is transmitted through the liquid or gas without change to any point.
Pascal's law was discovered by the French scientist B. Pascal in 1653, this law is confirmed by various experiments.
Pressure is a physical quantity equal to the modulus of the force F acting perpendicular to the surface, which is per unit area S of this surface.
Pascal's law formula Pascal's law is described by the pressure formula:
\(p = \dfrac(F)(S)\)
where p is the pressure (Pa), F is the applied force (N), S is the surface area (m2).
Pressure is a scalar quantity It is important to understand that pressure is a scalar quantity, that is, it has no direction.
Ways to reduce and increase pressure:
In order to increase the pressure, it is necessary to increase the applied force and/or reduce the area of its application.
Conversely, to reduce pressure, it is necessary to reduce the applied force and/or increase the area of its application.
The following types of pressure are distinguished:
- atmospheric (barometric)
- absolute
- excess (gauge)
Gas pressure depends on:
- from the mass of gas - the more gas in the vessel, the greater the pressure;
- on the volume of the vessel - the smaller the volume with a gas of a certain mass, the greater the pressure;
- from temperature - with increasing temperature, the speed of movement of molecules increases, which interact more intensely and collide with the walls of the vessel, and therefore the pressure increases.
Liquids and gases transmit in all directions not only the pressure exerted on them, but also the pressure that exists inside them due to the weight of their own parts. The upper layers press on the middle ones, and the middle ones on the lower ones, and the lower ones on the bottom.
There is pressure inside the liquid. At the same level, it is the same in all directions. With depth, pressure increases.
Pascal's law means that if, for example, you press on a gas with a force of 10 N, and the area of this pressure is 10 cm2 (i.e. (0.1 * 0.1) m2 = 0.01 m2), then the pressure in the place where the force is applied will increase by p = F/S = 10 N / 0.01 m2 = 1000 Pa, and the pressure in all places of the gas will increase by this amount. That is, the pressure will be transmitted without changes to any point in the gas.
The same is true for liquids. But for solids - no. This is due to the fact that the molecules of liquid and gas are mobile, and in solids, although they can vibrate, they remain in place. In gases and liquids, molecules move from an area of higher pressure to an area of lower pressure, so that the pressure throughout the volume quickly equalizes.
Unlike solids, liquids and gases in a state of equilibrium do not have elastic shape. They have only volumetric elasticity. In a state of equilibrium, the voltage in a liquid and gas is always normal to the area on which it acts. Tangential stresses cause only changes in the shape of elementary volumes of the body (shears), but not the magnitude of the volumes themselves. For such deformations in liquids and gases, no effort is required, and therefore, in these media at equilibrium, tangential stresses do not arise.
law of communicating vessels in communicating vessels filled with a homogeneous liquid, the pressure at all points of the liquid located in the same horizontal plane is the same, regardless of the shape of the vessels.
In this case, the surfaces of the liquid in communicating vessels are installed at the same level
The pressure that appears in a liquid due to the gravitational field is called hydrostatic. In a liquid at a depth \(H\), counting from the surface of the liquid, the hydrostatic pressure is equal to \(p=\rho g H\) . The total pressure in a liquid is the sum of the pressure at the surface of the liquid (usually atmospheric pressure) and hydrostatic pressure.
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