Pascal's law and its application hydraulic press. Hydraulic Press. Examples of problems with solutions

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 – contribute to the inculcation of a culture of mental work, create conditions for increasing interest in the material being studied.

Equipment:

· presentation, video clips

cards with individual tasks

During the classes.

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 looked at three different state of aggregation substances 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.

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 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? (The pressure of an explosion 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 a corked bottle, exerts 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 liquid glass inflates 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 with the help of 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.

v Are the cylinders and pistons the same? What is the difference?

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

v What law is the operation of a hydraulic press based on?

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 areas of which are S1 and S2 (S2 > S1). According to Pascal's law, we have equality of pressure in both cylinders: p1=p2.

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.

F1/ F2 = S1/ S2.

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.

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

Demonstration of a video clip

5. Checking understanding: Answer the test questions.

	1 option	Option 2
	A) work B) pressure	A) Joule B) Pascal B) Newton


	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
	C) wheels are replaced by tracks	A) knife blades are sharpened D) knives are replaced with fishing line

	State the incorrect statement.	B) to the bottom of the vessel D) in all directions
		A) 1300 kg/m3

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, make a comparison table: “Pressure solids, liquids and gases"

Answer the test questions.

	1 option	Option 2
	Which physical quantity determined by the formula p = F/S? A) work B) pressure	Which of the following is the basic unit of measurement for pressure? A) Joule B) Pascal B) Newton
	Which of the following values can express pressure?	Express the pressure equal to 0.01 N/cm2 in Pa.
	What formula can be used to calculate the force of pressure?	What formula can be used to calculate pressure?
	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. The walls 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 m2. Calculate the pressure of the box.	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 mm2.
	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...	Which of the following values can express hydrostatic pressure? A) 1300 kg/m3

Definition

Hydraulic Press is a machine that operates on the basis of the laws of motion and equilibrium of fluids.

Pascal's law underlies the operating principle of a hydraulic press. The name of this device comes from the Greek word hydraulics - water. A hydraulic press is a hydraulic machine that is used for pressing (squeezing). A hydraulic press is used where greater force is needed, for example, when squeezing oil out of seeds. Using modern hydraulic presses, forces up to $(10)^8$newtons can be achieved.

The basis of the hydraulic machine is made up of two cylinders of different radii with pistons (Fig. 1), which are connected by a pipe. The space in the cylinders under the pistons is usually filled with mineral oil.

In order to understand the principle of operation of a hydraulic machine, you should remember what communicating vessels are and what is the meaning of Pascal's law.

Communicating vessels

Communicating vessels are vessels connected to each other and in which liquid can freely flow from one vessel to another. The shape of communicating vessels can be different. In communicating vessels, a liquid of the same density is established at the same level if the pressures above the free surfaces of the liquid are the same.

From Fig. 1 we see that, structurally, a hydraulic machine consists of two communicating vessels of different radii. The heights of the liquid columns in the cylinders will be the same if no forces act on the pistons.

Pascal's law

Pascal's law tells us that the pressure that external forces exert on a fluid is transmitted to it without change to all its points. The action of many hydraulic devices is based on Pascal's law: presses, brake systems, hydraulic drives, hydraulic boosters, etc.

Operating principle of a hydraulic press

One of the simplest and oldest devices based on Pascal's law is a hydraulic press, in which a small force $F_1$ applied to the piston does not large area$S_1$, is converted into a large force $F_2$, which acts on a large area $S_2$.

The pressure created by piston number one is:

The pressure of the second piston on the liquid is:

If the pistons are in equilibrium, then the pressures $p_1$ and $p_2$ are equal, therefore, we can equate the right-hand sides of expressions (1) and (2):

\[\frac(F_1)(S_1)=\frac(F_2)(S_2)\left(3\right).\]

Let us determine what the modulus of the force applied to the first piston will be:

From formula (4), we see that the value of $F_1$ is greater than the force modulus $F_2$ by $\frac(S_1)(S_2)$ times.

And so, using a hydraulic press, you can balance a much larger force with a small force. The ratio $\frac(F_1)(F_2)$ shows the gain in strength.

This is how the press works. The body that needs to be compressed is placed on a platform that rests on a large piston. Using a small piston, high pressure is created on the liquid. The large piston, together with the compressed body, rises, rests against a stationary platform located above them, the body is compressed.

From a small cylinder to a large one, liquid is pumped by repeated movement of a small-area piston. They do it as follows. The small piston rises, the valve opens, and liquid is sucked into the space under the small piston. When the small piston lowers the liquid, applying pressure to the valve, it closes, which opens the valve, which allows the liquid to flow into the large vessel.

Examples of problems with solutions

Example 1

Exercise. What will be the gain in force for a hydraulic press if, when acting on a small piston (area $S_1=10\ (cm)^2$) with a force $F_1=800$ N, the force obtained on the large piston ($S_2=1000 \ (cm)^2$) equal to $F_2=72000\ $ N?

What gain in strength would this press achieve if there were no friction forces?

Solution. The gain in force is the ratio of the modules of the received force to the applied one:

\[\frac(F_2)(F_1)=\frac(72000)(800)=90.\]

Using the formula obtained for a hydraulic press:

\[\frac(F_1)(S_1)=\frac(F_2)(S_2)\left(1.1\right),\]

Let's find the gain in force in the absence of friction forces:

\[\frac(F_2)(F_1)=\frac(S_2)(S_1)=\frac(1000)(10)=100.\]

Answer. The gain in strength in the press in the presence of friction forces is equal to $\frac(F_2)(F_1)=90.$ Without friction it would be equal to $\frac(F_2)(F_1)=100.$

Example 2

Exercise. Using hydraulic lifting mechanism, you should lift a load with mass $m$. How many times ($k$) must the small piston be lowered in time $t$, if at one time it lowers a distance $l$? The ratio of the areas of the lift pistons is equal to: $\frac(S_1)(S_2)=\frac(1)(n)$ ($n>1$). The efficiency of the machine is $\eta $ when its engine power is $N$.

Solution. Schematic diagram The operation of a hydraulic lift is shown in Fig. 2, it is similar to the operation of a hydraulic press.

As a basis for solving the problem, we use an expression connecting power and work, but at the same time we take into account the efficiency of the lift, then the power is equal to:

The work is done with the aim of lifting the load, which means we will find it as a change in the potential energy of the load; we will consider the energy of the load at the point where it begins to rise ($E_(p1)$=0) to be zero potential energy, we have:

where $h$ is the height to which the load was raised. Equating the right-hand sides of formulas (2.1) and (2.2), we find the height to which the load was raised:

\[\eta Nt=mgh\to h=\frac(\eta Nt)(mg)\left(2.3\right).\]

We find the work done by force $F_0$ when moving a small piston as:

\[A_1=F_0l\ \left(2.4\right),\]

The work done by the force that moves the large piston upward (compresses the hypothetical body) is equal to:

\[A_2=FL\ .\] \[A_1=A_2\to F_0l=FL\] \[\frac(F_0)(F)=\frac(L)(l)=\frac(S_1)(S_2)\ left(2.5\right),\]

where $L$ is the distance by which the large piston moves in one stroke. From (2.5) we have:

\[\frac(S_1)(S_2)=\frac(L)(l)\to L=\frac(S_1)(S_2)l\ \left(2.6\right).\]

In order to find the number of piston strokes (the number of times the small piston will lower or the large one will rise), the height of the load should be divided by the distance by which the large piston moves in one stroke:

Answer.$k=\frac(\eta Ntn)(mgl)$

The action of the press is based on Pascal's law. A hydraulic press consists of two communicating vessels filled with liquid (usually technical oil) and closed by pistons of different sizes S 1 and S 2 (Fig. 1).

An external force acting on a small piston creates pressure

According to Pascal's law, it is transmitted by a liquid in all directions without change. Therefore, a force acts on the second piston from the liquid side

(1)

A hydraulic press gives a gain in force as many times as the area of the larger piston exceeds the area of the small piston.

Force F 1 also changes the potential energy of the fluid in the press. But since the gravity of this liquid is much less than the force F 1. we considered the liquid to be weightless. In this regard, it should be noted that in real conditions, equation (1) is satisfied only approximately.

The press does not give any benefit in work. Indeed, when the small piston is lowered, the force does work A 1 = F 1 h 1, where h 1 is the stroke of the small piston. Part of the liquid from the narrow cylinder is displaced into the wide one, and the large piston rises by h 2. Work of force F 2

(2)

But liquid is incompressible. Consequently, the volumes of liquids transferred from one cylinder to another are equal, i.e.

Substituting this equation and equation (1) into (2), we obtain A 1 = A 2 .

A hydraulic press allows you to develop colossal forces and is used for pressing products (from metal, plastic, from various powders), for pushing holes in metal sheets, for testing materials for strength, for lifting weights, for squeezing oil from seeds in oil mills, for pressing plywood, cardboard, hay. In metallurgical plants, hydraulic presses are used to make steel machine shafts, railroad wheels, and many other products.

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 comprehend the practical significance and 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 – contribute to the inculcation of a culture of mental work, create conditions for increasing interest in the material being studied.

Equipment :

presentation, video clips

individual task cards

During the classes.

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?

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

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 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 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? What is the difference?

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.

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.

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

Demonstration of a video clip

5. Checking understanding : Answer the test questions.

p = F/ S?

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 measurement for 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

Attention! The site administration is not responsible for the content of methodological developments, as well as for the compliance of the development with the Federal State Educational Standard.

Participant: Kolesnikov Maxim Igorevich
Head: Shcherbinina Galina Gennadievna

Purpose of the work: experimental confirmation of Pascal's law.

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, excavators... Thus, Pascal's law has found great application in 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 see for myself and convince my classmates, many of whom believe that it is stupid to waste time on “antiquity” when we are surrounded 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. Classic of French literature, one of the founders mathematical analysis, theory of probability 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.

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 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.