Presentation on the topic "pressure gauge". Pressure measuring instruments Special ammonia pressure gauge

Measuring instruments atmospheric pressure

Physics Presentation

7th grade

Sharonova S.M.

Pressure is a physical quantity that shows effective force per unit surface area perpendicular to that surface. Pressure is defined as P = F / S, where P is pressure, F is pressure force, S is surface area. From this formula it is clear that pressure depends on the surface area of the body acting with a certain force. The smaller the surface area, the greater the pressure.

The unit of measurement for pressure is newton per square meter(H/m2). We can also convert pressure units N/m2 to pascals, a unit of measurement named after the French scientist Blaise Pascal, who developed the so-called Pascal's Law.

1 N/m2 = 1 Pa.

Torricelli. His mercury tube was the first barometer.

The cup barometer is an improved version of the Torricelli barometer.

For scientific and everyday purposes, you need to be able to measure atmospheric pressure. For this there are special devices- barometers. The very first device for measuring atmospheric pressure was invented...

No matter what size cup of mercury you take, no matter what diameter the tube is, the mercury will always rise to the same height - 760 mm. The barometric tube can be given different shape, only one thing is important, one end of the tube must be closed so that there is no air from above.

You can fill the tube with any liquid other than mercury, but you must remember to change its length.

Water barometers were built by Pascal (Rouen, 1646) ...

... and Otto von Guericke (Magdeburg, 1660)

The largest water barometer, 12 m high, was constructed in 1987 by Bert Bolle, curator of the Barometer Museum in Martensdijk, the Netherlands, where it is installed.

Mercury barometers provide accurate readings but require great care when handling them. The modern barometer is made liquidless!

It's called an aneroid barometer. Metal barometers are less accurate, but not as bulky or fragile.

Internal structure of an aneroid.

This barometer is called a barometric altimeter or altimeter.

An aneroid barometer is a very sensitive instrument. For example, going up to the top floor of 9 storey building, due to the difference in atmospheric pressure on different heights we will detect a decrease in atmospheric pressure of 2-3 mmHg. Art.

A barometer can be used to determine the flight altitude of an aircraft.

The idea of Pascal's experiment formed the basis for the design of the altimeter. It determines the altitude above sea level by changes in atmospheric pressure.

When observing the weather in meteorology, if it is necessary to record fluctuations in atmospheric pressure over a certain period of time, they use recorder- barograph.

To measure pressure, different units are used: mm of mercury, physical atmospheres,

in the SI system

Pascals.

All living organisms are adapted to live at certain values of atmospheric pressure. Humans and most animals do not tolerate high altitude conditions well, but some birds reach significant heights in flight. The condor bird can rise to a height of up to 9000m, mountain jackdaws - up to 8200m, vultures and hawks - up to 6000-7000m, eagle - up to 5000m, other birds stay at an altitude of no more than 4000m.

The largest water barometer, 12 m high, was constructed in 1987 by Bert Bolle, curator of the Barometer Museum in Martensdijk, the Netherlands, where it is installed.

Can a person produce a pressure of 1000 atm? Yes, by sticking a needle into the fabric!

Remember the experience of Otto von Guericke - 1654 in the city of Magdeburg. It turns out that " Magdeburg hemispheres“every person has: the heads of the femurs are held in the pelvic joint by atmospheric pressure.

How can a driver help a friend and pour gasoline from his car into the gas tank of another? There is such a simple device - a siphon. Its work is based on the action of atmospheric pressure.

The structure of the Earth's atmosphere resembles a multi-story building.

The first “floor” is the troposphere: up to 11 km high at sea level, it contains 4/5 of the mass of all air, the temperature drops with height, and clouds form here.
The second “floor” is the stratosphere: up to 55 km above sea level, contains 1/5 of all air, the kingdom of cold with a temperature of about minus 40 degrees Celsius, the ozone layer is located here.
The third “floor” is the mesosphere: up to 200 km above sea level, the air is very rarefied, the pressure is 1/25000 of normal atmospheric pressure.

The fourth “floor” is the thermosphere: unprecedented heat of about 1000-2000 degrees Celsius, air density is extremely low, falling meteors ignite here.
The fifth “floor” is the exosphere: the outer shell of the atmosphere, up to 600 km high, the strongest air rarefaction; even higher, signs of air particles can be traced to an altitude of more than 1000 km.

ABOUT STRANGE FISH - STICKED

This fish sticks to the shark with such force that it is impossible to tear it off. This live hook is still used in Australia to catch sharks and large fish, and in South America– turtles. With the help of stick fish, fish weighing up to 18 kg are caught. There are metal vacuum lifting devices. These suction cups are metal or rubber bowls similar to Magndeburg hemispheres with a diameter of 50 to 600 mm; they can lift loads weighing up to 700 kg. By attaching several suction cups to an object, you can lift a load weighing up to 10 tons!

IN Lately in medicine they began to use a “liquid scalpel”, i.e. tissue incision during surgery is carried out with a thin stream of saline solution under a pressure of about 120 atmospheres.

LET'S THINK ABOUT "5"?

1. What is the difference between the change in air density with height and the density of water at different sea depths? 2. Which barometer is more sensitive: mercury or oil? Why? 3. Is it possible to measure the pressure on board? space station a mercury barometer, or an aneroid?

4. What type of barometer should be used to measure internal pressure spaceship when it is moving with the engine off? Why?

Option 7-3-1
1. Determine the area of one tractor caterpillar, which, with a mass of 3880 kg, exerts a pressure on the ground of 4 N/sq.cm? 2. For a smaller piston hydraulic machine area 5 sq.cm. a force of 2500 N acts. What load is lifted by the machine with a large piston whose area is 200 sq.cm? 3. What pressure does a layer of kerosene 0.6 meters high exert on the bottom of the vessel? 4. With what force does the air press on a table with an area of 0.7 square meters? Why do we not experience the action of this force when we lift the table? 5. Water is poured into one elbow of communicating vessels to a height of 10 cm; to what height should mercury be poured into the other elbow in order to achieve equilibrium of the liquids in the vessel’s elbows?
Everyone decides their own option

Option 7-3-2.

1. What pressure does it exert on the ground? Brick wall 2.5 meters high?

2. The pump pumps oil into the hydraulic press under a pressure of 30 N/cm2. With what force does the press compress the pressed part if the area of the press piston is 0.08 sq.m.?

H. There is a side hole in the kerosene tank, closed with a plug with an area of 8 sq.cm. What magnitude of force must keep the plug from flying out if the hole is at a depth of 1.8 meters?

4. Determine the force with which the atmosphere presses on window glass with an area of 1.5 sq.m. Why doesn’t the glass shatter into pieces from such terrible force?

5. Water is poured into one elbow of communicating vessels to a height

6 cm. To what height should you pour kerosene into the other elbow to achieve equilibrium of liquids in the legs of the vessel?

Option 7-3-3.

1. A tractor having a support area of two tracks of 2.4 sq.m. produces a pressure on the ground equal to 5 N/cm2. Determine the mass of the tractor.

2. The area of small piston of hydraulic machine is 10 times less area second piston. What force must be applied to the large piston to keep a 1 kg load on the small piston in balance?

3. The pipe can withstand pressure of 500,000 N/sq.m. To what height can water be supplied through this pipe?

4. With what force does the atmosphere press on a person whose skin surface area is 2 square meters? Why does a person not notice the effect of this force on himself?

5. In communicating vessels of the same shape there are 10 cubic meters. cm of water and 10 cc. kerosene. What is the difference in fluid levels in the right and left vessels?

Option 7-3-4.

1. Find the area of the piston, which, under pressure on it compressed air 48 N/sq.cm. develops a force of 120,000 N.

2. A cubic vessel with a volume of 1 cubic meter. filled with water. Determine the pressure at the bottom of the vessel.

H. In a cylinder under a piston with an area of 0.1 sq.m. there are 9 kg of water. What is the pressure on the bottom of the cylinder if a 1 kg weight is placed on the piston in stages?

4. Air pressure at an altitude of 10 km is 26000 Pa. With what force does the air in an airplane squeeze out a window glass with an area of 800 sq. cm?

5. There are 10 cubic cm in communicating vessels of the same shape. water and 3 cc. mercury What is the difference in fluid levels in the right and left vessels?

Option 7-3-5.

1. What should be the area of the skis so that a person weighing 70 kg exerts a pressure of no more than 0.5 N/cm2 on the snow?

2. Hydraulic machine piston with an area of 2 cm2. is lowered by a force of 150 N. What is the weight of the load lifted by the second piston of area 8 cm2?

H. The fountain's water rises to a height of 5 m. What is the water pressure in the pipe supplying water to the fountain?

4. What force of atmospheric pressure acts on a notebook sheet with an area of 350 sq. cm? Why doesn't this sheet tear under the influence of such enormous force?

5. On one side of the communicating vessels, water was poured to a height of 4 cm, and on the other, an unknown liquid was poured, which needed to be poured to a height of 5 cm before reaching equilibrium in the communicating vessels. What kind of liquid is this?

Answers

task\option

7 - 3 - 1

7 - 3 - 2

7 - 3 - 3

7 - 3 - 4

7 - 3 - 5

density 800 kg/m 3, most likely it is kerosene

Slide 1

Slide 2

* Atmosphere (Greek “atmos” - steam, air and “sphere” - ball) is the air shell surrounding the Earth. The atmosphere extends to a height of several thousand kilometers from the Earth's surface. The surface of the Earth is the bottom of the ocean of air. The surface of the Earth and all bodies on it experience pressure from the entire thickness of air. This pressure is called atmospheric pressure.

Slide 3

* Confirmation of the existence of atmospheric pressure. The existence of atmospheric pressure can explain many phenomena that we encounter in life. Let's look at some of them. The figure shows a glass tube, inside of which there is a piston that fits tightly to the walls of the tube. The end of the tube is lowered into the water. If you lift the piston, then water will rise behind it. This happens because when the piston rises, an airless space is formed between it and the water. Water rises into this space under pressure from outside air following the piston.

Slide 4

* In 1654, Otto Guericke in the city of Magdeburg, in order to prove the existence of atmospheric pressure, performed such an experiment. He pumped the air out of the cavity between the two metal hemispheres folded together. The pressure of the atmosphere pressed the hemispheres so tightly against each other that eight pairs of horses could not tear them apart.

Slide 5

*Torricelli experience. Atmospheric pressure was first measured by the Italian scientist Evangelista Torricelli in the experiment that bears his name. The pressure of a column of mercury 1 mm high is equal to: 1 mm Hg = 133.3 Pa 1 hPa (hectopascal) = 100 Pa.

Slide 6

* Torricelli noticed that the height of the mercury column in the tube changes, and these changes in atmospheric pressure are somehow related to the weather. If you attach a vertical scale to a tube of mercury, you get the simplest mercury barometer (Greek “baros” - heaviness, “metreo” - measure) - a device for measuring atmospheric pressure. Conclusion:

Slide 7

* Students write in their notebook: The unit of atmospheric pressure is 1 mm Hg. Art. Relationship between Pa and mm. Hg P= ρgh = 13,600 kg/m3 9.8 N/kg 0.001 m = 133.3 Pa 1 kPa = 1000 Pa 1 hPa = 100 Pa 760 mmHg ≈ 101 300 Pa ≈ 1013 hPa Units of atmospheric pressure.

Slide 8

Atmospheric pressure in wildlife Flies and tree frogs can stay on window glass thanks to tiny suction cups in which a vacuum is created and atmospheric pressure holds the suction cup on the glass. Sticky fish have a suction surface consisting of a series of folds that form deep “pockets.” When you try to tear the suction cup away from the surface to which it is stuck, the depth of the pockets increases, the pressure in them decreases, and then the external pressure presses the suction cup even harder. *

Slide 9

* The elephant uses atmospheric pressure whenever it wants to drink. His neck is short, and he cannot bend his head into the water, but only lowers his trunk and draws in air. Under the influence of atmospheric pressure, the trunk fills with water, then the elephant bends it and pours water into its mouth. The suction effect of the swamp is explained by the fact that when you raise your leg, a rarefied space is formed under it. The excess of atmospheric pressure in this case can reach 1000 N/per foot area of an adult. However, the hooves of artiodactyl animals, when pulled out of a quagmire, allow air to pass through their incision into the resulting rarefied space. The pressure from above and below the hoof is equalized, and the leg is removed without much difficulty.

Fragments from the presentation

Test

Which scientist proposed a way to measure atmospheric pressure?
What letter represents atmospheric pressure?
What is the unit of atmospheric pressure?
What is the name of the device for measuring atmospheric pressure?
What is the value of normal atmospheric pressure?
What is the name of the altitude measuring device used in aviation?

Pressure gauges– instruments for measuring pressures greater or less than atmospheric pressure (from the Greek “manos” - rare, loose and “metreo” - I measure.

Pressure gauges are:

liquid
metal

Liquid pressure gauge

A liquid pressure gauge consists of a two-legged glass tube into which some liquid is poured.
Design and principle of operation of an open liquid pressure gauge

Metal pressure gauge device

Metal tube bent into an arc
Lever arm
Toothwort
Arrow

Pressure gauges are used in all cases where it is necessary to know, control and regulate pressure. Most often, pressure gauges are used in heat power engineering, chemical and petrochemical enterprises, and food industry enterprises.

Sphygmomanometer (tonometer)- measuring device blood pressure. It consists of a cuff that is placed on the patient's arm, a device for inflating air into the cuff, and a pressure gauge that measures the air pressure in the cuff. Also, the sphygmomanometer is equipped with either a stethoscope or electronic device, registering air pulsations in the cuff.

Consolidation

What devices did we meet today?
Why are the fluid levels in both elbows the same in an open pressure gauge?
Why do the liquid levels in the pressure gauge elbows change when the box is immersed in water?
How can you use a liquid pressure gauge to show that at the same depth the pressure is the same in all directions?
How does a metal pressure gauge work?
In what units is the scale of a metal pressure gauge calibrated?

Municipal autonomous educational institution

"Lyceum No. 7" Berdsk

Pressure gauges Piston Liquid Pump Hydraulic Press

7th grade

Physics teacher I.V.Toropchina

Pressure gauges

To measure more or less

atmospheric pressure is used pressure gauges

(from Greek "manos" - loose, "metreo" - I measure).

There are pressure gauges liquid and metal .

Liquid pressure gauge

The liquid pressure gauge consists of a double-bend glass tube,

into which some liquid is poured. With flexible

tubes, one of the pressure gauge elbows is connected to a round flat

a box covered with rubber film.

Liquid pressure gauge

The operation of the pressure gauge is based on comparing the pressure in a closed

knee with external pressure in the open knee. The deeper

immerse the box in liquid, the larger it becomes

the difference in the heights of the liquid columns in the pressure gauge elbows, and thus

more pressure is produced by the liquid.

Metal pressure gauge

Using a metal pressure gauge

measure the pressure of compressed air and other gases.

1.A metal tube bent into an arc

2. Arrow

3.Zubchatka

4. Crane

5. Lever

Metal pressure gauge device

The end of the tube communicates with the help of tap 4 with the vessel in which the pressure is measured.

As the pressure increases, the tube

unbends. Closed movement

its end using lever 5 and

teeth 3 are transmitted to the arrow

2, moving near the instrument scale.

When the pressure decreases, the tube

(due to its elasticity)

returns to previous position, A

arrow - to zero division

scales.

Application of pressure gauges

Pressure gauges are used in all cases where

need to know, control and regulate

pressure. Most often, pressure gauges are used in

thermal power engineering, chemical, petrochemical

enterprises, food industry enterprises.

A manometer for measuring blood pressure is called: tonometer

Piston Liquid Pump

Action of piston liquid pumps based

on the fact that under the influence of atmospheric pressure

the water in the tube rises behind the piston .

Piston liquid pump design

1 – piston 2 – 2 – valves

Pump operating principle

When the piston moves up water, under the influence of atmospheric pressure, enters the pipe, lifts the lower valve and moves behind the piston. When the piston moves down The water under the piston presses on the bottom valve and it closes.

Pump operating principle

At the same time, under water pressure, the valve inside opens

piston, and water passes into the space above the piston. At

subsequent upward movement of the piston, the

the water above it, which is poured into the barrel. Behind the piston

a new portion of water rises, which upon subsequent lowering of the piston

will be above him, etc.

How does it work piston pump with an air chamber?

1-piston

2-suction valve

3-discharge valve

4-air chamber

5-handle

Mechanisms that operate using some kind of liquid are called hydraulic (Greek “hydro” - water, liquid).

The main part of a hydraulic machine is two cylinders of different diameters, equipped with pistons and connected by a tube.
The space under the pistons and the tube are filled with liquid (usually mineral oil).
The heights of the liquid columns in both cylinders are the same as long as no forces act on the pistons.

Hydraulic machine formula

Let us denote the forces acting on the pistons - F 1 And F 2 , piston areas - S 1 And S 2 .

Then the pressure under the small piston is: p 1 = F 1 S 1 , and under the big one: p 2 = F 2 S 2 .
According to Pascal's law, pressure is transmitted equally in all directions by a fluid, therefore p 1 = p 2 Substituting the corresponding values, we get