Chapter 6

Elements of fluid mechanics

Pressure in liquid and gas

Gas molecules, performing a random, chaotic movement, are not connected or very weakly connected by interaction forces, therefore they move freely and, as a result of collisions, tend to scatter in all directions, filling the entire volume provided to them, i.e. the volume of gas is determined by the volume of the vessel in which gas occupies.

Like a gas, a liquid takes the shape of the container in which it is contained. But in liquids, unlike gases, the average distance between molecules remains almost constant, so the liquid has an almost constant volume.

Although the properties of liquids and gases differ in many respects, in a number of mechanical phenomena their behavior is determined by the same parameters and identical equations. That's why hydroaeromechanics- a branch of mechanics that studies the equilibrium and movement of liquids and gases, their interaction with each other and the solid bodies flowing around them, - uses unified approach to study of liquids and gases.

In mechanics, with a high degree of accuracy, liquids and gases are considered as solid, continuously distributed in the part of space they occupy. The density of a liquid depends little on pressure. The density of gases depends significantly on pressure. It is known from experience that the compressibility of liquid and gas in many problems can be neglected and a single concept can be used incompressible fluid- a liquid whose density is the same everywhere and does not change with time.

If a thin plate is placed in a liquid at rest, then the parts of the liquid located along different sides from it, will act on each element of its surface with forces , which, regardless of how the plate is oriented, will be equal in magnitude and directed perpendicular to the platform, since the presence of tangential forces would cause the fluid particles to move (Fig. 44).

A physical quantity determined by the normal force acting on the part of a liquid per unit area is called pressure R liquids:

Pressure unit - Pascal(Pa): 1 Pa is equal to the pressure created by a force of 1 N, uniformly distributed over a surface normal to it with an area of ​​1 m 2 (1 Pa = 1 N/m 2).

Pressure at equilibrium of liquids (gases) obeys Pascal's law(French scientist (1623-1662)): the pressure in any place of a fluid at rest is the same in all directions, and the pressure is equally transmitted throughout the entire volume occupied by the fluid at rest.

Let's consider how the weight of a liquid affects the pressure distribution inside a resting incompressible liquid. When a fluid is in equilibrium, the horizontal pressure is always the same, otherwise there would be no equilibrium. Therefore, the free surface of a liquid at rest is always horizontal, away from the walls of the vessel. If a fluid is incompressible, then its density does not depend on pressure. Then at cross section S, height h and density of the liquid column, its weight, and the pressure to the bottom base

Pressure in liquid and gas.

The gas presses on the walls of the vessel in which it is enclosed. If slightly inflated balloon place it under a glass bell and pump out the air from under it, the ball will become inflated. What happened? Outside there is almost no air pressure; the air pressure in the ball caused it to stretch. Conclusion : gas exerts pressure.

Let us prove the existence of pressure inside the liquid.

Pour water into a test tube, the bottom of which is covered with rubber film. The film bends. Why? It bends under the weight of the liquid column. Therefore, this experiment confirms the existence of pressure inside the liquid. The film stops bending. Why? Because the elastic force of the rubber film is balanced by the force of gravity acting on the water. If we increase the column of liquid, what will happen? The higher the liquid column, the more the film bends.

Conclusion : There is pressure inside the liquid.

How is gas pressure explained based on the theory of molecular motion?

The pressure of gas and liquid on the walls of blood vessels is caused by the impacts of gas or liquid molecules.

What does pressure in liquid and gas depend on?

Pressure depends depending on the type of liquid or gas; on their temperature . When heated, the molecules move faster and hit the wall of the container harder.

What else does the pressure inside them depend on?

Why can’t explorers of the ocean and sea depths sink to the bottom without special devices: bathyscaphes, bathyspheres?

A glass of water is on display. The force of gravity acts on the liquid. Each layer, with its weight, creates pressure on other layers.

To answer the question: what else does pressure in a liquid or gas depend on, let us determine empirically.

(U Students are divided into 4 groups, which empirically check the following answers to the questions):

1. Is the fluid pressure the same at the same level from bottom to top and from top to bottom?

2. is there pressure on side wall vessel?

3. Does the pressure of a liquid depend on its density?

4. Does the pressure of a liquid depend on the height of the liquid column?

Assignment to group 1

Is the fluid pressure the same at the same level from bottom to top and from top to bottom?

Pour colored water into the test tube. Why did the film bend?

Place the test tube in a vessel with water.

Monitor the behavior of the rubber film.

When did the film straighten?

Make a conclusion: is there pressure inside the liquid, is the pressure of the liquid the same at the same level from top to bottom and from bottom to top? Write it down.

Assignment to group 2

Is there pressure on the side wall of the vessel and is it the same at the same level?

Fill the bottle with water.

Open the holes at the same time.

Watch how water flows out of the holes.

Make a conclusion: is there pressure on the side wall, is it the same at the same level?

Task for group 3

Does fluid pressure depend on the height of the column (depth)?

Fill the bottle with water.

Open all the holes in the bottle at the same time.

Watch for trickles of water flowing out.

Why is water leaking?

Draw a conclusion: does pressure in a liquid depend on depth?

Assignment to group 4

Does pressure depend on the density of a liquid?

Pour water into one test tube and sunflower oil into the other, in equal quantities.

Do the films sag equally?

Draw a conclusion: why films bend; Does the pressure of a liquid depend on its density?

Pour water and oil into glasses.

Density clean water– 1000 kg/m3. Sunflower oil – 930 kg/m3.

Conclusions.

1 . There is pressure inside the liquid.
2 . At the same level, it is the same in all directions.
3 . The greater the density of a liquid, the greater its pressure.

4 . With depth, pressure increases.

5 . Pressure increases with temperature.

Let us confirm your conclusions with several more experiments.

Experience 1.

Experience 2. If a fluid is at rest and in equilibrium, will the pressure be the same at all points within the fluid? Inside a liquid, the pressure should not be the same at different levels. At the top is the smallest, in the middle is the average, at the bottom is the largest.

The pressure of a liquid depends only on the density and height of the liquid column.

The pressure in the liquid is calculated by the formula:

p = gρh ,

Whereg= 9.8 N/kg (m/s 2)- acceleration free fall; ρ- liquid density;h- height of the liquid column (immersion depth).

So, To find the pressure, it is necessary to multiply the density of the liquid by the magnitude of the acceleration of gravity and the height of the liquid column.

In gases, the density is many times less than the density of liquids. Therefore, the weight of the gases in the vessel is small and its weight pressure can be ignored. But if we're talking about about large masses and volumes of gases, for example, in the atmosphere, then the dependence of pressure on altitude becomes noticeable.

Pascal's law.

By applying some force, we will force the piston to enter the vessel a little and compress the gas located directly below it. What will happen to the gas particles?

Particles settle under the piston more densely than before .
What do you think will happen next? Due to mobility, gas particles will move in all directions. As a result, their arrangement will again become uniform, but more dense than before. Therefore, the gas pressure will increase everywhere and the number of impacts on the walls of the vessel will increase. When expanding, it will decrease.

The additional pressure was transferred to all gas particles. If the gas pressure near the piston itself increases by 1 Pa, then at all points inside the gas it will increase by the same amount.

Experiment: We connect a hollow ball with narrow holes to a tube with a piston. Let's fill the ball with water and push the piston into the tube. What are you observing? IN The water will flow out of all holes evenly.

If you press on a gas or liquid, the increase in pressure will be “felt” at every point of the liquid or gas, i.e. the pressure exerted on a gas is transmitted to any point equally in all directions. This statement is called Pascal's law.

Pascal's law: liquids and gases transmit the pressure exerted on them in all directions equally.

This law was discovered in the 17th century by the French physicist and mathematician Blaise Pascal (1623-1662), who discovered and investigated the series important properties liquids and gases. Experiments confirmed the existence of atmospheric pressure, discovered by the Italian scientist Torricelli.

The action of Pascal's law in life:

= in a spherical shape soap bubbles(air pressure inside the bubble is transmitted in all directions without change);

Shower, watering can;

When a football player hits the ball;

IN car tire(when inflated, the increase in pressure is noticeable throughout the entire tire);

IN hot-air balloon…

So, we have looked at the transmission of pressure by liquids and gases. The pressure exerted on a liquid or gas is transmitted to any point equally in all directions.

Why are compressed gases contained in special cylinders?

Compressed gases exert enormous pressure on the walls of the vessel, so they have to be enclosed in durable steel special cylinders.

So, unlike solids, individual layers and small particles of liquid and gas can freely move relative to each other in all directions.

Pascal's law finds wide application and in technology:

= heating system: thanks to pressure, the water warms up evenly ;

Pneumatic machines and tools,

Jackhammer,

Sandblasting machines(for cleaning and wall painting),

Air brake,

Jack, Hydraulic Press, compressed air open the doors of subway trains and trolleybuses.

As you know, gravity acts on all bodies on Earth: solid, liquid, and gaseous.
Let's consider liquids. Pour water into a vessel that has a flexible membrane instead of a bottom. We observe how the rubber film begins to sag. It is not difficult to guess that under the influence of gravity the weight of the liquid column presses on the bottom of the vessel. Moreover, the higher the level of liquid poured, the more the rubber membrane stretches. After the rubber bottom bends, the water stops (comes to equilibrium), since in addition to the force of gravity, the elastic force of the rubber membrane acts on the water, which balances the force of water pressure on the bottom.
Let's consider whether the liquid presses on the walls of the vessel? Take a vessel with holes in the side wall. Let's pour water into it. And quickly open the holes. We see a picture very similar to the experiment with Pascal's ball. But at the same time there is no external pressure We did not influence the liquid. To explain this experience, it is necessary to recall Pascal's law.
Each layer of liquid, each molecule with its weight presses on the lower layers. Moreover, according to Pascal's law, this pressure is transmitted in all directions and equally, in contrast to solid bodies, the weight of which acts only in one direction. This is how the lower layers of liquid in the vessel are affected. large quantity liquid molecules than on the upper ones - the pressure in the lower part of the vessel is greater. And as a result, the water pressure from the lower hole is much greater.
Let's do one more experiment. Place a flask with a falling off bottom in a large vessel with water. To do this, first press the bottom tightly with a rope. When the vessel is in the water, you can release the rope. What pressed the bottom tightly to cylindrical vessel? The bottom is pressed against the walls of the vessel by water pressure, which acts from bottom to top.
Now slowly and carefully begin to add water into the empty vessel. As soon as the levels of liquids in both vessels become equal, the bottom will fall away from the vessel.
Since the water pressure forces inside and outside the cylinder have become the same, the bottom will behave in the same way as in the air - as soon as we let go of the rope, the bottom will fall away due to gravity.
At the moment of separation, the liquid column in the vessel presses from top to bottom, and the pressure of a liquid column of the same height, but located in the jar, is transmitted from bottom to top to the bottom.
All these experiments can also be carried out with other liquids. The result will be the same.
Empirically, we have established that there is pressure inside the liquid. At the same level, it is the same in all directions. With depth, pressure increases. Gases also have weight, which is why both liquids and gases have similar pressure transfer properties. However, gas has a much lower density than liquid. Let's talk about another amazing and seemingly impossible phenomenon, which is called the “hydrostatic paradox”. Let's use a special device to demonstrate this phenomenon.
We use three vessels in the experiment different shapes, filled with liquid to one level. The bottom area of ​​all vessels is the same and is closed with a rubber membrane. The poured liquid stretches the membrane. By bending, the rubber film presses on the lever and deflects the arrow of the device.
The instrument needle deviates equally in all three cases. This means that the pressure created by the liquid is the same and does not depend on the weight of the liquid poured. This fact is called the hydrostatic paradox. This is explained by the fact that liquids, unlike solids, will also transfer some of the pressure to the walls of the vessels.

On this topic

“Pressure in liquid and gas”

Student 7 “B” Class

Secondary school No. 1

Lezhnina Petra

Pressure-magnitude, equal to the ratio The force acting perpendicular to a surface to the area of ​​that surface is called pressure. A unit of pressure is taken to be the pressure produced by a force of 1 N acting on a surface with an area of ​​1 m 2 perpendicular to this surface.

Therefore, to determine the pressure, the force acting perpendicular to the surface must be divided by the surface area: It is known that gas molecules move randomly. As they move, they collide with each other, as well as with the walls of the container containing the gas. There are many molecules in a gas, and therefore the number of their impacts is very large. For example, the number of impacts of air molecules in a room on a surface with an area of ​​1 cm 2 in 1 second. expressed as a twenty-three digit number. Although the impact force of an individual molecule is small, the effect of all molecules on the walls of the vessel is significant, and it creates gas pressure.

So, the pressure of the gas on the walls of the vessel (and on the body placed in the gas) is caused by impacts of gas molecules. It is known that gas molecules move randomly. As they move, they collide with each other, as well as with the walls of the container containing the gas. There are many molecules in a gas, and therefore the number of their impacts is very large. For example, the number of impacts of air molecules in a room on a surface with an area of ​​1 cm 2 in 1 s is expressed as a twenty-three-digit number. Although the impact force of an individual molecule is small, the effect of all molecules on the walls of the vessel is significant, and it creates gas pressure. So, the pressure of the gas on the walls of the vessel (and on the body placed in the gas) is caused by impacts of gas molecules.

As the volume of a gas decreases, its pressure increases, and as the volume increases, the pressure decreases, provided that the mass and temperature of the gas remain unchanged.

The pressure exerted on a liquid or gas is transmitted without change to each point in the volume of the liquid or gas (Pascal's law).

Based on Pascal's law, it is easy to explain the following experience. The figure shows a hollow ball with various places

If the ball is filled with smoke, then when the piston is pushed into the tube, streams of smoke will begin to come out of all the holes in the ball. This confirms (that gases transmit the pressure exerted on them equally in all directions.)

Let's lower the tube with a rubber bottom, into which water is poured, into another, wider vessel with water. We will see that as the tube is lowered, the rubber film gradually straightens. Full straightening of the film shows that the forces acting on it from above and below are equal. Complete straightening of the film occurs when the water levels in the tube and vessel coincide.

So, experience shows that there is pressure inside the liquid and at the same level it is equal in all directions. With depth, pressure increases. Gases are no different from liquids in this respect.

Formula for calculating the pressure of liquid at the bottom of a vessel. From this formula it is clear that the pressure of the liquid at the bottom of the vessel depends only on the density and height of the liquid column.

Diaphragm pressure gauge. How to measure the pressure of a liquid on a surface solid? How to measure, for example, the pressure of water at the bottom of a glass? Of course, the bottom of the glass is deformed under the influence of pressure forces, and knowing the magnitude of the deformation, we could determine the magnitude of the force that caused it and calculate the pressure; but this deformation is so small that it is practically impossible to change it indirectly. Since it is convenient to judge the pressure exerted on it by a liquid by the deformation of a given body only when the deformations are large enough, then for the practical determination of liquid pressure they use special devices- pressure gauges, in which the deformations have a relatively large, easily measurable value.

The simplest membrane pressure gauge is designed as follows. A thin elastic plate M - membrane - hermetically closes an empty box K. A pointer P is attached to the membrane, rotating about the O axis. When the device is immersed in a liquid, the membrane bends under the influence of pressure forces, and its deflection is transferred in an enlarged form to the pointer moving along the scale. Each position of the pointer corresponds to a certain deflection of the membrane, and therefore a certain force of pressure on the membrane. Knowing the area of ​​the membrane, we can move from pressure forces to the pressures themselves. You can directly measure pressure if you calibrate the pressure gauge in advance, i.e. determine what pressure a particular pointer position on the scale corresponds to. To do this, you need to expose the pressure gauge to pressures, the magnitude of which is known and, noticing the position of the pointer arrow, put the corresponding numbers on the instrument scale.

The air shell surrounding the Earth is called the atmosphere (from the Greek words: atmos-vapour, air and sphere-ball).

The atmosphere, as shown by observations of the flight of artificial Earth satellites, extends to an altitude of several thousand kilometers. We live at the bottom of a huge

air ocean. The surface of the Earth is the bottom of this ocean.

Due to gravity, the upper layers of air, like ocean water, compress the lower layers. The air layer adjacent directly to the Earth is compressed the most and, according to Pascal's law, transmits the pressure exerted on it in all directions.

As a result of this, the earth's surface and the bodies located on it experience the pressure of the entire thickness of the air, or, as they usually say, experience atmospheric pressure.

In practice, to measure atmospheric pressure, a metal barometer is used, called an aneroid (translated from Greek as “without liquid.” The barometer is called this because it does not contain mercury).

The appearance of the aneroid is shown in the figure. main part it is a metal box 1 with a wavy (corrugated) surface. The air has been pumped out of this box, and so that atmospheric pressure does not crush the box, its lid is pulled upward with a spring 2. As atmospheric pressure increases, the lid bends down and tightens the spring. As the pressure decreases, the spring straightens the cap. An arrow-pointer 4 is attached to the spring using a transmission mechanism 3, which moves to the right or left when the pressure changes. Under the arrow there is a scale, the divisions of which are marked according to the readings of the mercury barometer. Thus, the number 750, against which the aneroid arrow stands, shows that in this moment height in mercury barometer mercury 750 mm.

Therefore, the atmospheric pressure is 750 mmHg. Art., or » 1000 hPa.

Knowing the atmospheric pressure is very important for predicting the weather for the coming days, since changes in atmospheric pressure are associated with changes in weather. A barometer is a necessary instrument for meteorological observations.

List of used literature:

1. Physics textbooks for grades 7-9.

2. Elementary textbook of Physics (volume 1-2).

3. Handbook of Physics for schoolchildren.

4. Internet.(www.big-il.com)

Organization: branch of MBOU Lyceum village. Dolgorukovo in the village. Millstone

Locality: s. Millstone

Repeat - a general lesson on the topic: “Pressure of liquids and gases.”

Strive to comprehend science more and more deeply,

Thirst for the knowledge of the eternal.

Only the first knowledge

the light will shine on you.

You will find out: there is no limit to knowledge.

Ferdowsi

Lesson objectives: repeat and test the knowledge gained from studying pressure in liquids and gases, and knowledge physical formulas necessary to solve problems;

Lesson objectives:

Educational:

summarize the material on the topic “Pressure in liquids and gases,” repeat basic concepts and laws, and consolidate basic skills on this topic.

Developmental task:

broadening the horizons of students, about the manifestation and use of atmospheric pressure in nature and everyday life, its impact on the human body, discussing issues and solving problems that require students’ creative initiative.

Educational task:

fostering student attentiveness, the ability to work in a team, and the formation of a scientific worldview. Promote mutual assistance in the classroom.

1.Message of the topic of the lesson.

In today's lesson we will repeat how pressure in liquids and gases is determined and what role this physical quantity plays in our lives.

In order to answer all the questions posed, you need to know how pressure arises in liquids and gases.

And 1 student (FI) will help us with this

He will tell us what the atmosphere of our planet is like.

(The title of the report appears on the screen: “The Atmosphere of Our Planet.”)

Teacher. If a person does not feel this pressure, why did people need to know about its existence? And who was the first to

did you measure?

We will learn this from the next message that was prepared for us (student 2). and it is called “The History of the Discovery of Atmospheric Pressure.”

Teacher. From the message we learned that they could determine atmospheric pressure for a long time.

But what determines the pressure in liquids and gases, and whether you know about it, I will find out after you answer the test questions. (I hand out the test on cards and the answers on the screen.)

Academician: Well, do you know what pressure depends on, and by what formula is it determined? (the guys write the formula). Now, using the formula for determining pressure, we will solve the problem. (Student solves on the board)

Task 1.

What pressure does the person in it exert on the bottom of the canister? machine oil, if the height of its layer is 50cm? (density 900kg/m3).

Given: Solution

h =50cm 0.5m р=ρgh

ρ=900kg/m 3 p=900kg/m 3 *10n/kg*0.5m =4500Pa

R -?

How does pressure change in the atmosphere?

Before answering this question, let’s listen to the poem “Aibolit”.

This is how it is said in famous poem K. Chukovsky. (Lines of the poem and a picture appear on the screen.) The student reads the poem.

And the mountains stand in front of him on the way,

And he begins to crawl through the mountains.

And the mountains are getting higher, and the mountains are getting steeper

And the mountains go under the very clouds

Oh, if I don't get there,

If I get lost on the way,

What will happen to them, to the sick, to my forest animals?

Teacher: What prevented the doctor from overcoming the mountains? (The guys answer that atmospheric pressure changes with altitude).

Let's solve the problem (490L)

At the foot of the mountain the barometer shows 98642 Pa, and at its top 90317 Pa. Determine the height of the mountain.

Given: Solution

р 1 =98642Pa h=▲h (р 1 - р 2)/133

p 2 =90317Pa h=12m*(98642Pa -90317Pa) /133 =750m

h -? Answer: 750m.

Now solve problem No. 488 yourself.

What conclusion can you draw from the solved problems? (From the problems it follows that the higher we rise above the surface of the Earth, the less pressure, and the lower above the surface of the earth, the higher.)

And now from the message “The role of atmospheric pressure in the life of humans and animals.” we will learn how a person uses atmospheric pressure in his life.

If you listened carefully to the message, this will help you answer the following questions. I announce the “Auction for the sale of fives.” (Questions appear on the screen and then the correct answers).

1. If you press it tightly to your lips Maple Leaf and quickly draw in air, the sheet breaks with a crash. Why? (When inhaling, the chest expands, and a vacuum is created in the oral cavity. From the outside, the leaf is affected great strength atmospheric pressure.)

2. If you open the tap in a barrel filled with water and the lid tightly closed. Which no longer has any, even small holes and cracks, then water will soon stop flowing from the tap. Why?

3. Why doesn’t water pour out of a glass partially filled with water if it is tightly covered with paper and turned upside down?

(answer: after turning the glass over, a rarefied space is formed between the bottom and the water, so the water is held in the glass by the force of atmospheric pressure from outside.)

4. Why does water rise up when it is drawn through a straw?

(when water is drawn in, the chest expands and a vacuum is created in the mouth, while the force of atmospheric pressure acts on the surface of the water. The pressure difference causes the water to rise up the straw.)

5.Can an astronaut draw ink into a piston pen while in a spaceship in a state of weightlessness?

(Yes, it can, if the ship maintains normal atmospheric pressure.)

Teacher. As can be seen from these questions, we can explain many physical phenomena knowing the existence of atmospheric pressure.

But also knowing about changes in pressure, we can predict changes in weather.

Student No. 4 will tell us about this in his message “Weather Prediction.”

Teacher. But people have long noticed that the behavior of some animals is associated with changes in the weather. And many weather-related signs appeared. Let's remember them now. (students name these signs one by one).

Teacher. Scientists, understanding the mechanisms of living nature, strive to recreate them in the form of instruments that accurately mark the slightest changes environment. Based on these observations, riddles related to physical phenomena and instruments were created. Now let’s take a break and guess a few riddles.

1. There is an invisible one;

Doesn't ask to come into the house

And before people run

In a hurry (air)

2. There is a plate hanging on the wall,

An arrow moves across the plate

This arrow is forward

Tells us the weather (barometer)

3. Passes through the nose into the chest

And the way back is on its way

He's invisible and yet

We cannot live without it modem. (air)

4. We go up the mountain

It became difficult for us to breathe

What kind of devices are there?

To measure pressure (barometer).

Teacher. The pressure arising in liquids and gases plays a huge role in our life. Therefore, in order to explain the physical phenomena associated with pressure, we must know how to determine it and with what instruments to measure it.

I think that ours will help you answer many questions related to atmospheric pressure.

Homework.

Reflection.

Children, depict in the form of a drawing what mood you were in during the physics lesson. Did you like the lesson?

If yes, then draw a smiling face. If not, then sad.

Literature:

1. Reader on physical geography.
2. T.P. Gerasimova “Geography” 6th grade. Textbook for general education. establishments. M.: Bustard
3. Great encyclopedia Nature "Water and Air"
4. A.V. Vladimirov "Stories about atmospheric pressure»
5. S. E. Polyansky “developments in physics”
6. Lukashik V.I. Collection of problems in physics: Textbook for students of 7-8 grades. avg. school
7. Peryshkin A.V. Physics. 7th grade: Textbook. for general education. establishments. M.: Bustard, 2015
8. Internet resources.

Application.

Test-survey

1.How is Pascal's law formulated?

A) the result of the force depends not only on its modulus, but also on the area of ​​the surface perpendicular to which it acts.

B) the gas pressure on the walls of the vessel is equal in all directions.

C) when the volume of a gas decreases, its pressure increases, and when the volume increases, it decreases.

D) The pressure exerted on a liquid or gas is transmitted without change to every point of the liquid or gas.

2. Which of the following units is accepted as a unit of pressure?

A) Newton b) Watt c) Pascal d) kilogram.

3. what pressure does a tank weighing 40 tons exert on the soil if the track surface is 2 m 2 ?

A) 10 kPa b) 20 kPa c) 1000 Pa d) 2000 Pa.

4. when a bullet hits the glass, a small hole remains in it, and when it hits an aquarium with water, the glass breaks into pieces. Why?

A) in water the speed of a bullet decreases

B) the increase in water pressure breaks the glass in all directions.

C) the bullet changes its trajectory in the water.

D) due to the sharp deceleration of the bullet in the water.

5. What is the height of the kerosene column in the vessel if the pressure at the bottom of the vessel is 1600 Pa? The density of kerosene is 800kg/m3.

A) 2m b) 20cm c) 20m d) 2cm

Answers: 1d 2c 3b 4b 5a