2.5.2. The simplest hydraulic machines.
Hydraulic Press. Multiplier
2.5.1. Pressure measuring instruments
Piezometers. Let us immerse glass tubes open at both ends into an "absolutely" at rest liquid so that their lower ends coincide with the 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 comparison plane. This height is equal to the height of the total hydrostatic head, measured not by absolute, but by excess pressure.
Fig.2.11. Pressure distribution law
in an "absolutely" fluid at rest
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 small 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 - by 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 figurative pressure gauge (Fig. 2.12).
Rice. 2.12. Differential pressure gauge
Differential pressure gauges can measure as excess (Fig. 2.11, A), and the vacuum pressure (Fig. 2.11, b). If with the help of such a manometer, usually filled with mercury, the pressure difference is measured in a liquid with a density that completely fills the connecting tubes, then
When measuring small gas pressures, alcohol, kerosene, water, etc. are used instead of mercury.
Piezometers and differential pressure gauges are applicable for measuring pressure not only in a liquid at rest, but also in a flow.
To measure pressures of more 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 action of a measured pressure. Through the mechanism, this deformation is transmitted to the arrow, which shows the value of the measured pressure on the dial.
Along with mechanical pressure gauges, electrical pressure gauges are used. A membrane is used as a sensitive element (sensor) in an electromanometer. Under the action of the measured pressure, the membrane is deformed and moves the potentiometer slider through the transmission mechanism, which, together with the pointer, is included in the electrical circuit.
The ratio of pressure units:
1at = 1kgf/cm 2 =10 m of water. st. = 736.6 mmHg Art. = 98066.5 Pa 10 5 Pa.
1 kPa = 10 3 Pa; 1 MPa = 10 6 Pa.
Under normal atmospheric pressure(0.1033 MPa) the height is 10.33 m for water, 13.8 m for gasoline (= 750 kg / m 3), 0.760 m for mercury, etc.
2.5.2. The simplest hydraulic machines. Hydraulic Press. Multiplier
Hydraulic Press. The press is used in engineering to create large compressive forces, which are necessary in technology for metal forming, 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. Diagram of a hydraulic press
One of the vessels has an area less than the area of the second vessel. If a force is applied to the piston in vessel 1, then a hydrostatic pressure is created under it, which is 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 so many times greater than the force acting on the piston in a small section, how many times the area is greater than the area.
The force is usually created by means of a piston pump, which supplies liquid (oil, emulsion) to the press chamber. The force can press the product between the piston and the fixed platform. In practice, the force developed is less than the force due to friction between pistons and cylinders. This reduction is taken into account by the efficiency of the press -. Forces of up to 100,000 tons and more are developed in modern hydraulic presses.
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 principle of operation 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 a lot of force is needed, such as pressing oil out of seeds. With the help of modern hydraulic presses it is possible to obtain force up to $(10)^8$newtons.
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 below the pistons is usually filled with mineral oil.
In order to understand the principle of operation of a hydraulic machine, one should remember what communicating vessels are and what is the meaning of pascal's law.
Communicating vessels
Communicating vessels are interconnected and in which liquid can freely flow from one vessel to another. The shape of the communicating vessels may be different. In communicating vessels, a fluid of the same density is set at the same level if the pressures above the free surfaces of the fluid are the same.
From Fig. 1 we see that structurally a hydraulic machine is two communicating vessels of different radii. The heights of the liquid columns in the cylinders will be the same if there are no forces acting on the pistons.
Pascal's law
Pascal's law tells us that the pressure exerted by external forces on a fluid is transferred to it without change at all its points. The operation of many hydraulic devices is based on Pascal's law: presses, brake systems, hydraulic drives, hydraulic boosters, etc.
The principle of operation of the 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 a piston of a small area $S_1$ is converted into a large force $F_2$ that acts on a large area $S_2$.
The pressure that piston number one creates 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 parts of expressions (1) and (2):
\[\frac(F_1)(S_1)=\frac(F_2)(S_2)\left(3\right).\]
Let's determine what will be the modulus of the force applied to the first piston:
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.
The press works like this. The body to be compressed is placed on a platform that rests on a large piston. A small piston creates a high pressure on the liquid. A large piston, together with a compressible body, rises, rests against a fixed platform located above them, the body is compressed.
From a small cylinder into a large liquid is pumped by repeated movement of the piston of a small area. Do it in the following way. 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, exerting pressure on the valve, it closes, and the valve opens, which passes the liquid into the large vessel.
Examples of problems with a solution
Example 1
Exercise. What will be the gain in strength of the hydraulic press if, when acting on a small piston (with an area of $S_1=10\ (cm)^2$) with a force of $F_1=800$ N, a force is obtained, the impact on a large piston ($S_2=1000 \ (cm)^2$) equal to $F_2=72000\ $ H?
What gain in strength would this press have if there were no friction forces?
Solution. The gain in force is the ratio of the modules of the received force to the applied force:
\[\frac(F_2)(F_1)=\frac(72000)(800)=90.\]
Using the formula obtained for the hydraulic press:
\[\frac(F_1)(S_1)=\frac(F_2)(S_2)\left(1.1\right),\]
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 force 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 a hydraulic lifting mechanism, a load having a mass $m$ should be lifted. How many times ($k$) must the small piston be lowered in time $t$ if it is lowered by a distance $l$ at one time? The ratio of lift piston areas is: $\frac(S_1)(S_2)=\frac(1)(n)$ ($n>1$). The efficiency of the machine is $\eta$ with the power of its engine $N$.
Solution. The schematic diagram of the operation of the 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 that relates 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 that we will find it as a change potential energy load, we will consider the energy of the load at the place of the beginning of its rise ($E_(p1)$=0) as zero potential energy, we have:
where $h$ is the height to which the load was lifted. Equating the right parts 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 the force $F_0$ when moving the small piston as:
\[A_1=F_0l\ \left(2.4\right),\]
The work of the force that moves the large piston up (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 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 strokes of the pistons (the number of times that the small piston goes down or the big one rises), the height of the load should be divided by the distance that the big piston moves in one stroke:
Answer.$k=\frac(\eta Ntn)(mgl)$
OPERATING PRINCIPLE AND CLASSIFICATION
The hydraulic press is a machine-tool of almost static action. The principle of operation of a hydraulic press is based on Pascal's law. IN general view the press consists of two chambers equipped with pistons (plungers) and connected pipelines (Fig. 20.1, a). If to the piston 1 apply force, then pressure is created under it. According to Pascal's law, pressure is transmitted to all points of the liquid volume and, being directed normally to the base of the large piston 2 , creates a force that exerts pressure on the workpiece 3 .
Based on Pascal's law,
The force is so many times greater than the force, how many times the area is greater than the area.
The structural diagram of the hydraulic press is shown in fig. 20.1, b. Working cylinder 4 , in which the working plunger moves 5 , fixed in the upper fixed cross member 6 . The latter with the help of columns 7 connected to fixed crossbar 9 installed on the foundation. Lower 9 and top 6 the crossbars together with the columns form the press frame. working plunger 5 connected to the movable crossbar 8 , which has a direction along the columns, and tells it to move in only one direction - down. Return cylinders are installed to lift the movable cross member. 10 with plungers 11 .
Cylinders are sealed to prevent leakage of pressurized fluid 12 .
The main parameter of a hydraulic press is the nominal force of the press - the product of the nominal pressure of the liquid in the press cylinder and the active area of its working plungers.
Presses, depending on the technological purpose, differ from each other in the design of the main units, their location and number, as well as the value of the main parameters ( Z- open height of the die space; H- full travel of the movable crossbar, - table dimensions).
Rice. 20.1. Hydraulic Press:
A- operating principle; b– constructive scheme; V- scheme of a press with a movable bed
According to the technological purpose, hydraulic presses are divided into presses for metal (Fig. 20.2, A) and for non-metallic materials (Fig. 20.2, b). In turn, presses for metal are divided into five groups: for forging and stamping; for extrusion; for sheet stamping; for straightening and assembly work and for the processing of metal waste. In view of the wide variety of types of presses, we present the values of nominal forces, the most common of them.
From the first group of presses, one can name: forging - free forging with stamping in backing dies,; stamping (see, for example, Fig. 26.3) - hot forging of parts made of magnesium and aluminum alloys,; piercing - deep hot piercing of steel blanks in a closed matrix,; broaching - pulling steel forgings through rings,.
Rice. 20.3. Types of hydraulic press cylinders:
A- plunger type; b- differential plunger type; V- piston type
From the second group of presses, it is possible to note pipe-bar and rod-profile presses - pressing non-ferrous alloys and steel,.
From the third group we will name the presses: single-action sheet-stamping (see, for example, Fig. 26.5),; exhaust - deep drawing of cylindrical parts,; for rubber stamping, ; for beading, flanging, bending and stamping of plate material, ; bending - bending of thick sheet material in a hot state,.
From the fifth group, we note baling and briquetting presses for compressing waste such as metal chips and sheet metal scraps,. Hydraulic presses for non-metallic materials include presses for powders, plastics and for pressing chipboard and board.
The technological purpose of the hydraulic press determines the design of the bed (column, two-column, single-column, special), type, design and number of cylinders (plunger, differential-plunger, piston, etc.).
The most widespread is the four-column fixed frame with the movement of moving parts in a vertical plane (see Fig. 20.1, b). Sometimes the frame of the press is made movable (Fig. 20.1, V).
On fig. 20.3 shows the main types of cylinders. Plunger and differential plunger type cylinders are single acting cylinders. The working cylinder of the differential plunger type is used when, for example, a needle must pass through the working plunger (pipe presses). Piston type cylinders are most often used when using oil as the working fluid. In this case, the sealing element of the piston itself will be piston rings. The piston type cylinder is a double acting cylinder.
A press with a lower location of the working cylinder and a fixed bed may not have return cylinders, in which case the moving parts return to their original position under the influence of their weight. The working cylinder is connected to the filling tank.
According to the number of working cylinders, the presses are divided into one-, two-, three- and multi-cylinder.
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 required to compress the sample material or lifting weights. The press consists of two communicating vessels - cylinders of different cross-sectional area, filled with liquid (oil or water) and closed with pistons from above. Pressure applied to the handle (lever, fig. 2.8, page 70). A force is applied to a piston of small diameter, which, according to Pascal's law, is transferred to a piston of a larger diameter, this piston moves up and performs useful work.
Let's introduce the notation: let F be the force on the press lever, F1- the force acting on the small piston No. 1 with an area S1, F2- the force developed by the large piston No. 2 with an area S2. 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 cuffs of the press, sealing the gaps, the dependence is valid that takes into account the efficiency 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. Such a battery is used when it is necessary to perform short-term work, for example, during the operation of locks and hydraulic lifts.
The accumulator consists of a twisted cylinder with weights and a fixed piston. The cylinder is filled with a working fluid using a pump, which raises it to the calculated height H.
The reserve of energy for work in the accumulator is equal to:
G- weight of the cylinder with weights; L- lifting height.
To raise the piston, it is necessary to pump fluid into the cylinder with a volume of:
Where S- sectional area of the cylinder.
Lifting force:
Where p is the pressure in the cylinder.
Then the work done to lift the load is:
A=GL=pV.
Rice. 2.9. hydraulic accumulator
efficiency battery:
Multiplier serves to increase the pressure in the oil lines of lubricators, etc.
The simplest multiplier in design consists of a cylinder, a piston with a rod, and stuffing box seals for the piston and rod (Fig. 2.10).
Rice. 2.10. Multiplier
in container A behind the piston fluid is supplied under some pressure p1 which pushes the piston with a force:
D is the diameter of the inner surface of the cylinder.
The movement of the piston and rod is resisted by forces
Where f 1 , f 2- coefficients of friction of sealing rings; n 1 , n 2 b 1 , b 2- the number of sealing rings; d– diameter.
The resultant 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.
Grade 7 Lesson #41 Date
Subject: Pascal's law. Hydraulic Press.
Lesson type: Lesson learning new material.
Goals and objectives of the lesson:
Educational goal - learn about Pascal's law, expand and deepen students' knowledge on the topic “Pressure”, discuss the difference between solids, liquids and gases; introduce a new concept of "Hydraulic press", help students to comprehend the practical significance, usefulness of the acquired knowledge and skills.
Development goal - create conditions for the development of research and creative skills; communication and collaboration skills.
educational goal - promote the instillation of a culture of mental work, create conditions for increasing interest in the material being studied.
Equipment :
presentation, video clips
personalized cards
During the classes.
1.Org. moment.
Preparing students for class work. Reception "Smile"
2. Motivation and setting goals and objectives of the lesson.
Picture slide show. The objectives of our lesson are:
- Today in the lesson 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 how to explain a number of physical phenomena using Pascal's law. See the application of the law in practice.
Explore physical foundations devices and operation of the hydraulic machine;
Give the concept of a hydraulic press and show its practical application.
3. Study new topic
All bodies are made up of molecules and atoms. We have considered three different states of aggregation of matter and based on the structure, they are different in properties. Today we have to get acquainted with the influence of pressure on solid, liquid and gaseous substances. Let's look at examples:
Drive a nail into the board with a hammer. What are we observing? In which direction is the pressure acting?
(Under the pressure of the hammer, the nail enters the board. In the direction of the force. The board and the nail are integral solids.)
Let's take the 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 film walls not only in the direction of the force, but also to the sides.)
Now let's see how the liquid behaves. Fill the tube with liquid. We press on the piston, observe and compare with the results of previous experience.
(The film takes the form of a ball, the liquid particles press in different directions equally.)
Let's take gas as an example. Let's inflate the ball.
(Pressure is transmitted by air particles equally in all directions.)
We considered the effect of pressure on solid bulk, liquid and gaseous substances. What similarity do you notice?
(For liquids and gases, pressure acts in different directions in the same way, 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). The particles in the gas are evenly distributed throughout the volume. Let's hit the piston. The particles under the piston are compacted. Due to their mobility, the 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 the pressure is transferred to all particles of the gas.
Let's do an experiment with Pascal's ball. Let us take a hollow ball, having narrow holes in various places, and attach it to a tube with a piston.
E 
If you draw water into the tube and press on the piston, then water will flow from all the holes of the ball in the form of streams.(Children make their guesses.)
Let us formulate a general conclusion.
The piston presses on the surface of the water in the tube. The water particles under the piston, condensing, transfer its pressure to other layers lying 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 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 from a pneumatic gun at a hard-boiled egg, then the bullet will pierce only a through hole in it, while the rest remains intact. But if you shoot a raw egg, it will shatter. (When fired at a boiled egg, the bullet pierces a solid body, so it pierces in the direction of flight because pressure is transferred in that direction.)
2. Why is a projectile explosion 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. An evil genie that is in a gaseous state inside corked bottle, exerts strong pressure on its walls, bottom and cork. How does a genie hit in all directions, if in a gaseous state it has neither arms nor legs? What law allows him to do this? (molecules, Pascal's law)
4. For astronauts, food is made in a 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 transferred equally in all directions, and liquid glass 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 wheel is broken, the driver easily lifts the car with the help of a device and changes the damaged wheel, despite the fact that the weight of the car is about 1.5 tons.
Let's answer the question together why is this possible?
He uses a jack. The jack belongs to hydraulic machines.
Mechanisms that work with the help of some kind of liquid are called hydraulic (Greek "gidor" - water, liquid).
Hydraulic Press is a material forming machine driven by a squeezable liquid.
answer the questions.
Are cylinders and pistons the same? What is the difference?
What does it mean: each piston does its own?
What is the principle behind the operation of a hydraulic press?
The device of the 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 S 1 and S 2 (S 2 > S 1 ). According to Pascal's law, we have equality of pressures in both cylinders: p 1=p2.
p1=F1/S1, P2=F2/ S2 , F1/S1= F2/ S2, F1 S2=F2 S1
During the operation of a hydraulic press, 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.
The principle of operation of the hydraulic press.
The body to be pressed is placed on a platform connected to a large piston. With the help of a small piston, a large pressure is created on the liquid. This pressure is transmitted without change to each point of the liquid filling the cylinders. Therefore, the same pressure acts on the larger piston. But since its area is larger, then 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 is raised, the body rests against the fixed upper platform and is compressed. The pressure gauge, which measures the pressure of a liquid, is a safety valve that automatically opens when the pressure exceeds the allowable value. From a small cylinder to a large liquid is pumped by repeated movements of the small piston.
Hydraulic presses are used where a lot of power is required. For example, for squeezing oil from seeds at oil mills, for pressing plywood, cardboard, hay. On metallurgical plants hydraulic presses are used in the manufacture of steel machine shafts, railway wheels and many other products. Modern hydraulic presses can develop 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, lifts are equipped with a hydraulic drive.
Hydraulic jacks and hydraulic presses are used in huge quantities for a variety of purposes - from pressing bandages onto wagon wheelsets to lifting drawbridge trusses to allow ships to pass on rivers.
Video demonstration
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
C) 10,000 Pa
D) 100 Pa
A) F \u003d pS
B) F = mg
C) 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
C) 13500 Pa
D) 480 Pa
2 .
A) 100 Pa
B) 200 MPa
B) 300 kPa
D) 0.5 Pa
B) at the bottom of the vessel
D) in all directions
A) 4000 Pa
B) 0.4 Pa
C) 0.004 Pa
D) 400 Pa
A) 1300 kg / m 3
B) 500m
C) 1500 Pa
D) 600 J
7. Peer review: 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 test questions.
Option 2
What physical quantity is determined by the formulap = F/ S?
A) work
B) strength
B) pressure
Which of the following units is the basic unit for measuring 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 equal to 0.01 N/cm 2, in Pa.
A) 1000 Pa
B) 10 Pa
C) 10,000 Pa
D) 100 Pa
What formula can be used to calculate the force of pressure?
A) F \u003d pS
B) F = mg
C) F= kx
What formula can be used to calculate pressure?
A ) F= pS
B ) p = F/S
B) P=pgh
List some of the words that are missing. Cutting tools are sharpened in order to ... pressure, because the more ... the area of \u200b\u200bsupport, the ... pressure.
A) reduce less; less
B) reduce; more; more
B) increase more; more
D) increase; less; more
List some of the words that are missing.CThe walls of buildings are installed on a wide foundation in order to ... pressure, since the more ... the area of \u200b\u200bthe support, 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 \u200b\u200bthe lower part of the foundation
B) truck tires are made wider
C) the wheels are replaced with caterpillars
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 tongs
C) they use a cart in summer, a sleigh in winter
D) knives are replaced with fishing line
A box weighing 0.96 kN has a footprint of 0.2 m 2 . Calculate the pressure of the box.
A) 4800 Pa
B) 135 Pa
C) 13500 Pa
D) 480 Pa
A force of 2 N acts on the needle during sewing. Calculate the pressure exerted by the needle if the area of the point is 0.01 mm 2 .
A) 100 Pa
B) 200 MPa
B) 300 kPa
D) 0.5 Pa
Point out the wrong statement.
A) gas pressure is created by impacts of randomly moving molecules
B) a gas exerts the same pressure in all directions
C) if the mass and temperature of the gas remain unchanged, then with a decrease in the volume of the gas, the pressure increases
D) if the mass and temperature of the gas remain unchanged, then with an increase in the volume of the gas, the pressure does not change
Pascal's Law states that liquids and gases transmit the pressure exerted on them...
A) in the direction of the force
B) at 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 of ..
A) 4000 Pa
B) 0.4 Pa
C) 0.004 Pa
D) 400 Pa
Which of the following values can express hydrostatic pressure?
A) 1300 kg / m 3
B) 500m
C) 1500 Pa
D) 600 J