Pascal's law and its application hydraulic press. Lesson "Pascal's Law. Hydraulic machines." Operating principle of a hydraulic press

The action of many hydraulic machines, for example, presses (jacks), is based on Pascal's law.

Hydraulic press(jack) is used to create large forces necessary to compress the sample material or lift weights. The press consists of two communicating vessels - cylinders of different cross-sectional areas, filled with liquid (oil or water) and closed on top with pistons. Pressure applied to the handle (lever, Fig. 2.8, page 70). A force is applied to a small-diameter piston, which, according to Pascal's law, is transferred to a larger-diameter piston; this piston moves upward and does useful work.

Let us introduce the notation: let F be the force on the press lever, F 1- force acting on small piston No. 1 with area S 1, F 2– force developed by large piston No. 2 with area S 2. An analytical representation of the operating principle of a hydraulic press is as follows:

.

Rice. 2.8. Hydraulic press

If it is necessary to take into account friction in the press cuffs that seal the gaps, the following relationship takes into account the efficiency factor η of the press:

Hydraulic accumulator(Fig. 2.9, p. 71) serves to accumulate the potential energy of the liquid, which is subsequently consumed as needed. This type of battery is used when it is necessary to carry out short-term work, for example, when operating locks and hydraulic lifts.

The accumulator consists of a coiled cylinder with weights and a stationary piston. The cylinder is filled with working fluid using a pump, which raises it to the design height H.

The energy reserve for operation in the battery is equal to:

G- weight of the cylinder with weights; L– load lifting height.

To raise the piston, it is necessary to pump liquid into the cylinder with a volume of:

Where S – cross-sectional area of ​​the cylinder.

Load lifting force:

Where p– pressure in the cylinder.

Then the work spent on lifting the load is:

A = GL=pV.

Rice. 2.9. Hydraulic accumulator

Efficiency battery:

Cartoonist serves to increase pressure in oil lines of lubricating devices, etc.

The simplest multiplier in design consists of a cylinder, a piston with a rod and gland seals for the piston and rod (Fig. 2.10).

Rice. 2.10. Cartoonist

Into container A Liquid is supplied behind the piston under some pressure p 1 which pushes the piston out with force:

D– diameter of the inner surface of the cylinder.

The movement of the piston and rod is resisted by forces

Where f 1, f 2- friction coefficients of sealing rings; n 1, n 2 b 1, b 2– number of sealing rings; d– diameter.

The resulting force acting on the piston creates pressure on the liquid in cavity B - behind the piston. The fluid pressure in this cavity will be greater, since the pressure area behind the piston is smaller than in front of the piston.

Class 7 Lesson No. 41 Date

Topic: Pascal's Law. Hydraulic press.

Lesson type: Lesson on learning new material.

Goals and objectives of the lesson:

Educational purpose - introduce Pascal's law, expand and deepen students’ knowledge on the topic “Pressure”, discuss the difference between solids, liquids and gases; introduce a new concept "Hydraulic press", help students understand practical significance, the usefulness of the acquired knowledge and skills.

Developmental goal – create conditions for the development of research and creative skills; communication and collaboration skills.

Educational goal – promote culture mental work, create conditions for increasing interest in the material being studied.

Equipment :

presentation, video clips

individual task cards

Progress of the lesson.

1.Org. moment.

Preparing students for work in class. Reception "Smile"

2. Motivation and setting goals and objectives of the lesson.

Demonstration of a slide with pictures. The objectives of our lesson are as follows:

- Today in class we will study one of the most important laws of nature, Pascal's law. The purpose of our lesson: to study the law, as well as learn to explain a number of physical phenomena using Pascal’s law. See the application of the law in practice.

Study the physical foundations of the design and operation of a hydraulic machine;

Give the concept of a hydraulic press and show its practical application.

3. Study a new topic

All bodies are made up of molecules and atoms. We examined three different states of aggregation of matter and, based on their structure, they differ in properties. Today we are going to get acquainted with the effect of pressure on solid, liquid and gaseous substances. Let's look at examples:

We drive the nail into the board with a hammer. What are we seeing? In what direction does the pressure act?

(Under the pressure of the hammer, the nail enters the board. In the direction of the force. The board and the nail are integral solid bodies.)

Let's take sand. This is a solid granular substance. Fill the tube with the piston with sand. One end of the tube is covered with a rubber film. We press on the piston and observe.

(Sand presses on the walls of the film not only in the direction of the force, but also to the sides.)

Now let's see how the liquid behaves. Let's fill the tube with liquid. We press on the piston, observe and compare with the results of the previous experiment.

(The film takes the shape of a ball, the liquid particles press equally in different directions.)

Let's look at the example of gas. Let's inflate the ball.

(Pressure is transmitted equally by air particles in all directions.)

We examined the effect of pressure on solid bulk, liquid and gaseous substances. What similarities did you notice?

(For liquids and gases, pressure acts equally in different directions, and this is a consequence of the random movement of a huge number of molecules. For solid bulk substances, pressure acts in the direction of the force and to the sides.)

Let us explain in more depth the process of pressure transfer by liquids and gases.

Imagine that a tube with a piston is filled with air (gas). Particles in the gas are distributed evenly throughout the volume. We press on the piston. The particles located under the piston are compacted. Due to their mobility, gas particles will move in all directions, as a result of which their arrangement will again become uniform, but more dense. Therefore, the gas pressure increases everywhere. This means that pressure is transmitted to all gas particles.

Let's do an experiment with Pascal's ball. Let's take a hollow ball that has narrow holes in various places and connect it to a tube with a piston.

E If you fill the tube with water and press the piston, water will flow out of all the holes in the ball in the form of streams.(Children express their guesses.)

Let us formulate a general conclusion.

The piston presses on the surface of the water in the tube. The water particles located under the piston, compacting, transfer its pressure to other layers that lie deeper. Thus, the pressure of the piston is transmitted to each point of the liquid filling the ball. As a result, some of the water is pushed out of the ball in the form of streams flowing out of all the holes.

The pressure exerted on a liquid or gas is transmitted without change to every point in the volume of the liquid or gas. This statement is called Pascal's law.

4. Consolidation: answer questions

1. If you shoot a hard-boiled egg from an air gun, the bullet will only make a through hole in it, while the rest remains intact. But if you shoot a raw egg, it will break into pieces. (When shooting at a boiled egg, the bullet pierces a solid body, so it pierces in the direction of flight since pressure is transmitted in this direction.)

2.Why is an explosion of a shell under water destructive for organisms living in water? (Explosion pressure in a liquid, according to Pascal's law, is transmitted equally in all directions, and animals can die from this)

3. The evil genie, which is in a gaseous state inside bottle, puts strong pressure on its walls, bottom and cork. Why does the genie kick in all directions, if in the gaseous state it has neither arms nor legs? What law allows him to do this? (molecules, Pascal's law)

4. For astronauts, food is prepared in semi-liquid form and placed in tubes with elastic walls. What helps astronauts squeeze food out of tubes?

(Pascal's law)

5. Try to explain the process of making glass vessels, when air is blown into a drop of molten glass?

(According to Pascal's law, the pressure inside the gas will be transmitted equally in all directions, and the liquid glass will inflate like a balloon.)

Application of Pascal's law in practice

Motivation for studying this topic: “Hydraulic press”

You have probably observed the situation: a tire is punctured, the driver, using the device, easily lifts the car and changes the damaged wheel, despite the fact that the car weighs about 1.5 tons.

Let's answer the question together: why is this possible?

He uses a jack. The jack is a hydraulic machine.

Mechanisms that operate using some kind of liquid are called hydraulic (Greek "gidor" - water, liquid).

Hydraulic press is a machine for processing materials by pressure, driven by a compressed liquid.

answer the questions.

Are the cylinders and pistons the same? How are they different?

What does it mean: each piston does its own thing?

On what law is the operation of a hydraulic press based?

The design of a hydraulic press is based on Pascal's law. Two communicating vessels are filled with a homogeneous liquid and closed by two pistons, the area of ​​which is S 1 and S 2 (S 2 > S 1 ). According to Pascal's law, we have equality of pressure in both cylinders: p 1 =p 2 .

p1=F1/S1, P2=F2/ S2 , F1/S1= F2/ S2, F1 S2=F2 S1

When a hydraulic press operates, a gain in force is created equal to the ratio of the area of ​​the larger piston to the area of ​​the smaller one.

F 1/ F 2 = S 1/ S 2.

Operating principle of a hydraulic press.

The pressed body is placed on a platform connected to a large piston. A small piston creates a lot of pressure on the liquid. This pressure is transmitted without change to every point of the liquid filling the cylinders. Therefore, the same pressure acts on the larger piston. But since its area is larger, the force acting on it will be greater than the force acting on the small piston. Under the influence of this force, the larger piston will rise. When this piston rises, the body rests against a stationary upper platform and is compressed. A pressure gauge, which measures the pressure of a liquid, is a safety valve that automatically opens when the pressure exceeds the permissible value. From the small cylinder to the large one, liquid is pumped by repeated movements of the small piston.

Hydraulic presses are used where greater force is required. For example, for squeezing oil from seeds in oil mills, for pressing plywood, cardboard, hay. In metallurgical plants, hydraulic presses are used in the manufacture of steel machine shafts, railway wheels and many other products. Modern hydraulic presses can produce hundreds of millions of newtons of force.

Millions of cars are equipped with hydraulic brakes. Tens and hundreds of thousands of excavators, bulldozers, cranes, loaders, and lifts are equipped with a hydraulic drive.

IN huge quantities Hydraulic jacks and hydraulic presses are used for a variety of purposes - from pressing tires onto carriage wheel sets to lifting drawbridge trusses to allow passage of ships on rivers.

Demonstration of a video clip

5. Checking understanding : Answer the test questions.

A) work

B) strength

B) pressure

A) Joule

B) Pascal
B) Newton

A) 40 mg

B) 0.1 kPa

B) 5 kN

2, in Pa.

A) 1000 Pa

B) 10 Pa

B) 10,000 Pa

D) 100 Pa

A) F= pS

B) F = mg

B) F= kx

A ) F= pS

B ) p = F/ S

B) P=pgh

A) reduce; less; less

B) reduce; more; more

B) increase; more; more

D) increase; less; more

A) reduce; more; less

B) reduce; more; more

B) reduce; less; less

D) increase; more; more

A) knife blades are sharpened

D) knives are replaced with fishing line

2 . Calculate the pressure of the box.

A) 4800 Pa

B) 135 Pa

B) 13500 Pa

D) 480 Pa

2 .

A) 100 Pa

B) 200 mPa

B) 300 kPa

D) 0.5 Pa

B) to the bottom of the vessel

D) in all directions

A) 4000 Pa

B) 0.4 Pa

B) 0.004 Pa

D) 400 Pa

A) 1300 kg/m 3

B) 500m

B) 1500 Pa

D) 600 J

7. Mutual check: exchange notebooks and check

Option 1: 1c, 2b, 3a, 4d, 5d, 6d, 7d, 8a

Option 2: 1b, 2d, 3a, 4a, 5d, 6b, 7d, 8c

6. Summing up. Homework. ξ 44.45 , draw up a comparative table: “Pressure of solids, liquids and gases”

Answer the test questions.

Option 2

What physical quantity is determined by the formulap = F/ S?

A) work

B) strength

B) pressure

Which of the following is the basic unit of pressure?

A) Joule

B) Pascal
B) Newton

Which of the following values ​​can express pressure?

A) 40 mg

B) 0.1 kPa

B) 5 kN

Express the pressure as 0.01 N/cm 2, in Pa.

A) 1000 Pa

B) 10 Pa

B) 10,000 Pa

D) 100 Pa

What formula can be used to calculate the force of pressure?

A) F= pS

B) F = mg

B) F= kx

What formula can be used to calculate pressure?

A ) F= pS

B ) p = F/ S

B) P=pgh

Indicate a number of words that are missing. Cutting tools are sharpened in order to…pressure, since the…the area of ​​support, the…the pressure.

A) reduce; less; less

B) reduce; more; more

B) increase; more; more

D) increase; less; more

Indicate a number of words that are missing.CThe shadows of buildings are installed on a wide foundation in order to…pressure, since the…the area of ​​support, the…the pressure.

A) reduce; more; less

B) reduce; more; more

B) reduce; less; less

D) increase; more; more

Find the wrong answer. They try to reduce pressure in the following ways:

A) increase the area of ​​the lower part of the foundation

B) truck tires are made wider

C) wheels are replaced by tracks

D) Reduce the number of columns supporting the platform

Find the wrong answer. They try to increase the pressure in the following ways

A) knife blades are sharpened

B) pliers are replaced with pliers

C) use a cart in summer, a sleigh in winter

D) knives are replaced with fishing line

A box weighing 0.96 kN has a support area of ​​0.2 m 2 . Calculate the pressure of the box.

A) 4800 Pa

B) 135 Pa

B) 13500 Pa

D) 480 Pa

A force of 2 N acts on the needle when sewing. Calculate the pressure exerted by the needle if the tip area is 0.01 mm 2 .

A) 100 Pa

B) 200 mPa

B) 300 kPa

D) 0.5 Pa

State the incorrect statement.

A) gas pressure is created by impacts of randomly moving molecules

B) the gas exerts equal pressure in all directions

C) if the mass and temperature of the gas remain unchanged, then as the volume of the gas decreases, the pressure increases

D) if the mass and temperature of the gas remain unchanged, then as the volume of the gas increases, the pressure does not change

Pascal's law states that liquids and gases transmit pressure exerted on them...

A) in the direction of the acting force

B) to the bottom of the vessel

B) in the direction of the resultant force

D) in all directions

A pressure of 4 kPa corresponds to a pressure...

A) 4000 Pa

B) 0.4 Pa

B) 0.004 Pa

D) 400 Pa

Which of the following values ​​can express hydrostatic pressure?

A) 1300 kg/m 3

B) 500m

B) 1500 Pa

D) 600 J

The action of a force on a solid body depends not only on the modulus of this force, but also on the surface area of ​​the body on which it acts. The interaction of liquids and gases with solids, as well as the interaction between adjacent layers of liquid or gas, also occurs not at individual points, but on a certain surface of their contact. Therefore, to characterize such interactions, the concept of pressure was introduced.

Pressure p call a value equal to the ratio of the modulus of the pressure force F acting perpendicular to the surface to the area 5 of this surface:

p=F/S. (5.1)

With a uniform distribution of pressure forces, the pressure on all parts of the surface is the same and is numerically equal to the pressure force acting on the surface of a unit area.

The pressure unit is determined from formula (5.1). In SI, the unit of pressure is taken to be the pressure caused by a force of 1 N, uniformly distributed over a surface with an area of ​​1 m 2 perpendicular to it. This unit of pressure is called pascal (Pa): 1 Pa = 1 N/m 2.

The following non-systemic pressure units are often used:

1. technical atmosphere (at): 1 at=9.8·10 4 Pa;
2. physical atmosphere (atm) equal to the pressure produced by a column of mercury 760 mm high. As shown in § 24, 1 atm = 1.033 atm = 1.013·10 5 Pa;
3. millimeter of mercury (mm Hg): 1 mm Hg. Art. » 133.3 Pa;
4. bar (in meteorology they use millibar); 1 bar=10 5 Pa, 1 mbar=10 2 Pa.

Pascal's law for liquids and gases

Solids transmit pressure exerted on them from the outside in the direction of the force that causes this pressure. Liquids and gases transmit external pressure quite differently.

Consider the following experiment (Fig. 48). There is water in a container sealed with a stopper. Three tubes of equal diameter are inserted into the cork, the lower holes of which are in the water at the same depth, but directed in different directions (down, sideways and up), as well as a tube that does not reach the water, to which a rubber spray bottle is connected. By pumping air into a vessel with its help, we increase the pressure exerted by the air on the surface of the water in the vessel. We notice that in all three tubes the water rises to the same height. Hence, a stationary liquid located in a closed vessel transmits the external pressure exerted on it in all directions equally(i.e. no change).

Observations show that external pressure and gases in a closed vessel also transmit. The described pattern was first discovered by the French scientist Pascal and was called Pascal's law.

Hydrostatic pressure

Each molecule of liquid located in the gravitational field of the Earth is affected by the force of gravity. Under the influence of these forces, each layer of liquid presses on the layers located underneath it. According to Pascal's law, this pressure is transmitted equally by the fluid in all directions. Hence, In liquids there is pressure due to gravity.

Observations show that a liquid in a vessel at rest puts pressure on the bottom and walls of the vessel and on any body immersed in this liquid. The pressure exerted by a fluid at rest on any surface in contact with it is called hydrostatic.

Hydrostatic Pressure Formula

Hydrostatic pressure can be determined using a device called a Pascal hydrostatic balance (Fig. 49). In the stand P, through which the annular pipe K passes, it is possible to hermetically seal vessels C of any shape that do not have a bottom. The movable bottom of these vessels is a flat round platform D suspended on the beam of an equal-arm scale, located near the lower hole of the pipe K. This platform is pressed against the end of the pipe by the force caused by the fact that a weight G is placed on the scale pan suspended on the other beam. A ruler L is attached to P, which is used to determine the height h of the liquid in a vessel mounted on a stand.

The experiment is carried out like this. A vessel in the shape of a straight circular cylinder is secured on a stand. Water is poured into it until the weight of this water becomes equal to the weight of the weight placed on the right pan of the scale, i.e. R w = R g. (Maintaining this amount of water is automatically ensured by the device itself, since if the weight of water in the vessel exceeds the weight of the weight, the bottom will open slightly and excess water will flow out.)

In a cylindrical vessel, the weight of the liquid P l = r f ghS, where f = rf is the density of the liquid, g is the acceleration of gravity, h is the height of the liquid column, S is the area of ​​the base of the cylinder, therefore the liquid exerts pressure on the bottom of the vessel

Formula (5.2) determines the value of hydrostatic pressure.

Theoretical derivation of the hydrostatic pressure formula

Let us select a stationary element of its volume inside a fluid at restDV in the form of a straight circular cylinder of height h with bases having a small areaDS, parallel to the free surface of the liquid (Fig. 50). The upper base of the cylinder is located from the surface of the liquid at a depth h 1, and the lower base is at a depth h 2 >h 1.

Three forces act vertically on the selected element of the liquid volume: pressure forces F 1 =p 1 DS and F 2 =p 2 DS (where p 1 and p 2 are the values ​​of hydrostatic pressure at depths h 1 and h 2) and gravity F t = rg DV = rgh DS.

The fluid volume element we have identified is at rest, which means F 1 +F 2 +F t =0, and therefore the algebraic sum of the projections of these forces onto the vertical axis is also equal to zero, i.e. p 2 DS-p 1 DS-rgh DS=0, from where we get

Let now the upper edge of the selected cylindrical volume of liquid coincide with the surface of the liquid, i.e. h 1 =0. Then h 2 =h and p 2 =p, where h is the immersion depth, and p is the hydrostatic pressure at a given depth. Assuming that the pressure p 1 =0 on the surface of the liquid (i.e., without taking into account the external pressure on the surface of the liquid), from (5.3) we obtain the formula for hydrostatic pressure p =rgh, which coincides with formula (5.2).

Communicating vessels

Vessels that have a channel filled with liquid between them are called communicating vessels. Observations show that in communicating vessels of any shape, a homogeneous liquid is always established at the same level.

Dissimilar liquids behave differently even in communicating vessels of the same shape and size. Let's take two cylindrical communicating vessels of the same diameter (Fig. 51), pour a layer of mercury on their bottom (shaded), and on top of it pour liquid with different densities into the cylinders, for example r 2 h 1).

Let us mentally select inside the tube connecting the communicating vessels and filled with mercury an area of ​​area S perpendicular to the horizontal surface. Since the liquids are at rest, the pressure on this area on the left and right is the same, i.e. p 1 =p 2 . According to formula (5.2), hydrostatic pressure p 1 = r 1 gh 1 and p 2 = r 2 gh 2 . Equating these expressions, we obtain r 1 h 1 2 h 2 , from which= r

Consequently, dissimilar liquids at rest are installed in communicating vessels in such a way that the heights of their columns turn out to be inversely proportional to the densities of these liquids.

If r 1 =r 2, then from formula (5.4) it follows that h 1 =h 2, i.e. homogeneous liquids are installed in communicating vessels at the same level.

Operating principle of a hydraulic press

A hydraulic press consists of two communicating vessels of cylindrical shape and different diameters, in which there are pistons whose areas S 1 and S 2 are different (S 2 >> S 1). The cylinders are filled with liquid oil (usually transformer oil). The hydraulic press device is shown schematically in Fig. 52 (this figure does not show the oil reservoir and valve system).

Without load, the pistons are at the same level. The piston S 1 is acted upon by a force F 1 , and a body to be pressed is placed between the piston S 2 and the upper support.

From this equality it follows that

Consequently, the forces acting on the pistons of a hydraulic press are proportional to the areas of these pistons. Therefore, with the help of a hydraulic press, you can obtain a gain in strength, the greater the S 2 greater than S 1 .

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• Participant: Kolesnikov Maxim Igorevich
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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.

Purpose 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; differently, such gas properties as compressibility and the ability to transmit pressure in all directions equally have found wide application in the design of various technical devices.

1. 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

1. 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.

1. In production, a pneumatic hammer and a pneumatic press are used for forging and processing metals.

1. 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.
2. 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 operating principle 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.

2.5.2. The simplest hydraulic machines.

Hydraulic press. Cartoonist

2.5.1. Pressure measuring instruments

Piezometers. Let us immerse glass tubes, open at both ends, into an “absolutely” resting liquid so that their lower ends coincide with points u (Fig. 2.11). In both tubes with open ends, the liquid will rise to the same height, which will lie on the water plane relative to the reference plane. This height is equal to the height of the total hydrostatic head, measured not by absolute pressure, but by excess pressure.

Fig.2.11. Law of pressure distribution

in an “absolutely” stationary fluid

Such tubes, open at both ends, designed to measure pressure, more precisely piezometric height, are called piezometers, or piezometric tubes.

Piezometers are suitable for measuring relatively low pressures because... Already with water in the tube it would rise to a height of 10 m, and mineral oil with a relative weight of 0.8 - to 12.5 m.

Differential pressure gauges. To measure the pressure difference at two points, differential pressure gauges are used, the simplest of which is a shaped pressure gauge (Fig. 2.12).

Rice. 2.12. Differential pressure gauge

Differential pressure gauges can measure both excess (Fig. 2.11, A), and vacuum pressure (Fig. 2.11, b). If, using such a pressure gauge, usually filled with mercury, the difference in pressure and density in a liquid that completely fills the connecting tubes is measured, then

When measuring small gas pressures, alcohol, kerosene, water, etc. are used instead of mercury.

Piezometers and differential pressure gauges are used to measure pressure not only in a fluid at rest, but also in a flow.

To measure pressures greater than 0.2-0.3, mechanical pressure gauges are used - spring or membrane. The principle of their operation is based on the deformation of a hollow spring or membrane under the influence of the measured pressure. Through the mechanism, this deformation is transmitted to a arrow, which shows the amount of pressure being measured on the dial.

Along with mechanical pressure gauges, electric pressure gauges are used. A membrane is used as a sensitive element (sensor) in an electromanometer. Under the influence of the measured pressure, the membrane is deformed and, through a transmission mechanism, moves the potentiometer slide, which, together with the pointer, is included in the electrical circuit.

Pressure unit ratio:

1at = 1kgf/cm 2 =10 m water st. = 736.6 mm Hg. Art. = 98066.5 Pa 10 5 Pa.

1 kPa = 10 3 Pa; 1 MPa = 10 6 Pa.

At normal atmospheric pressure (0.1033 MPa) the height is 10.33 m for water, 13.8 m for gasoline (= 750 kg/m3), 0.760 m for mercury, etc.

2.5.2. The simplest hydraulic machines. Hydraulic press. Cartoonist

Hydraulic press. The press is used in technology to create large compressive forces, which are necessary in technology when processing metals by pressure, pressing, stamping, briquetting, testing various materials, etc.

The press consists of communicating cylinders with pistons, connected to each other by a pipeline (Fig. 2.13).

Rice. 2.13. Hydraulic press diagram

One of the vessels has an area that is less than the area of ​​the second vessel. If force is applied to the piston in vessel 1, then hydrostatic pressure is created underneath it, determined by the formula.

According to Pascal's law, pressure is transmitted to all points of the fluid, including the area. It creates strength

Expressing through, we get

Thus, the force is as many times greater than the force acting on the piston in a small section as the area is greater than the area.

The force is usually created using a piston pump, which supplies liquid (oil, emulsion) into the press chamber. The force can press the product located between the piston and the stationary platform. The practically developed force is less than the force due to friction between the pistons and cylinders. This decrease is taken into account by the efficiency of the press -. In modern hydraulic presses, forces reach 100,000 tons or more.