What physical device measures atmospheric pressure with a thermometer. Instruments for measuring atmospheric pressure
One of the most accurate instruments used to measure atmospheric pressure at all meteorological stations is the so-called station cup barometer. It is a glass tube about 80 cm long, with a cross section of 1 cm2. Its upper end is sealed, and the lower open end is lowered into a cup of mercury. The tube is filled with mercury; in the unfilled part of the tube there is airless (or rather extremely rarefied) space.
To protect the tube from mechanical damage, it is enclosed in a metal frame. Schematic diagram of the design of a marine cup barometer: two longitudinal slits are made on both sides, one opposite the other, necessary to determine the height of the mercury column in the tube. On the left side of the front slit there is a scale: in old barometers - in millimeters, in new ones - in millibars. To read the pressure on a scale, a movable ring with a vernier is used. The vernier is moved along the slot using a screw located on the right side of the frame. Before counting, the lower cut of the vernier is brought to the upper point of the visible meniscus of mercury, and then the pressure is read out in tenths: wholes are counted along the lower cut of the vernier, and tenths - according to the divisions of the vernier (from 0 to 9). Tenths (mm or mb) are judged by the vernier division that exactly coincides with any division on the scale. To allow air to enter the cup with mercury, a small hole is made in it, loosely closed with a screw stopper.
The station cup barometer is installed in the weather station room in a special cabinet in a vertical position.
A marine mercury barometer, as its name suggests, is designed to measure atmospheric pressure on sea vessels. In principle, it is designed in the same way as a station cup barometer, and differs from it in its smaller size and narrower barometric tube with extensions at its ends. The narrowing of the middle part of the tube to the thickness of the capillary is done to reduce the vibration of mercury in the tube during the rocking of the ship and to protect against the penetration of air bubbles into the mercury. The cup with mercury is made narrower than in the station barometer. This also significantly eliminates the influence of the ship's pitching on the condition and barometer readings.
A marine barometer is suspended indoors on a ship using a gimbal.
An aneroid barometer, or simply aneroid, is a simple and easy-to-use instrument widely used for measuring atmospheric pressure on ships.
The operating principle of the aneroid is based on measuring the degree of deformation of the walls of a hollow flat metal pressure box under the influence of atmospheric pressure.
The aneroid box, being the sensing part of the device, reacts very sensitively to changes in atmospheric pressure. The sensitivity of the pressure box is achieved by the fact that the air in it is very highly discharged. When pressure increases, the box contracts, and when pressure decreases, it expands. To avoid complete deformation of the box, which is possible under the influence of atmospheric pressure, an arc-shaped spring is attached to it, which, by stretching the box, balances the atmospheric pressure acting on it.
The compression and tension of the box is transmitted to the barometer pointer through a system of rods and levers. The aneroid scale is graduated in either millimeters or millimeters of mercury. The aneroid is calibrated under the condition that the temperature of the pressure box at all pressure values is 0°. Therefore, to determine the correction for the aneroid reading, which depends on temperature, when reading the pressure, the temperature of the device itself is determined each time. The latter is determined by a thermometer mounted in an arcuate slot on the front surface of the aneroid.
The aneroid mechanism is enclosed in a round metal or plastic box, glazed on the front side. The device is always stored in a special case with an opening lid.
An aneroid barometer, compared to a mercury barometer, is a less accurate instrument, but it is almost insensitive to the rocking of the ship. This makes it more convenient to use and store in ship conditions. The main disadvantage of aneroids is the gradual decrease in their sensitivity and accuracy of indication due to the residual deformation of the aneroid box and spring that occurs over time. To eliminate these shortcomings, aneroids must be periodically checked in special institutions of the Hydrometeorological Service - in the verification bureau. Aneroids must be checked every six months.
The barograph is designed to continuously record changes in atmospheric pressure. Its structure is similar to that of a thermograph. It also consists of two main parts: receiving and writing. Several (5-10) aneron boxes connected to each other by metal gaskets serve as a pressure receiver. To avoid complete deformation of the boxes, which is possible under the influence of atmospheric pressure, a spring-type spring is built inside each of them.
Partial total deformation in the form of small vertical displacements of the entire series of pressure boxes, arising under the influence of changing atmospheric pressure, is transmitted through a system of levers to an arrow, at the end of which a feather is mounted.
The pressure is recorded in the form of a curve on a drum that rotates slowly using a clock mechanism. A paper tape is placed on the drum, marked with horizontal lines (pressure in mb) and vertical arcs (time in hours and minutes.
Depending on the time of full rotation of the drum, baroriffs are divided into “daily” and “weekly”.
Using a barograph, you can determine not only the specific value of atmospheric pressure at any time, but also the magnitude and nature of its change over any time interval.
Since the change in atmospheric pressure is very closely related to the current and upcoming weather, to predict it in sailing conditions it is important to know not so much the absolute value of the pressure as the magnitude and nature of its change over the past few hours.
The barograph on a ship is installed in a closed room using spring bars or attached to a special shelf or table.
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- Participant: Vertushkin Ivan Aleksandrovich
- Head: Elena Anatolyevna Vinogradova
Introduction
It's raining outside the window today. After the rain, the air temperature decreased, humidity increased and atmospheric pressure decreased. Atmospheric pressure is one of the main factors determining the state of weather and climate, so knowledge of atmospheric pressure is necessary in weather forecasting. The ability to measure atmospheric pressure is of great practical importance. And it can be measured with special barometer devices. In liquid barometers, as the weather changes, the liquid column decreases or increases.
Knowledge about atmospheric pressure is necessary in medicine, in technological processes, in human life and in all living organisms. There is a direct connection between changes in atmospheric pressure and changes in weather. An increase or decrease in atmospheric pressure can be a sign of weather changes and affect a person’s well-being.
Description of three interrelated physical phenomena from everyday life:
- Relationship between weather and atmospheric pressure.
- Phenomena underlying the operation of instruments for measuring atmospheric pressure.
Relevance of the work
The relevance of the chosen topic is that at all times people, thanks to their observations of animal behavior, could predict weather changes, natural disasters, and avoid human casualties.
The influence of atmospheric pressure on our body is inevitable; sudden changes in atmospheric pressure affect a person’s well-being, and weather-dependent people especially suffer. Of course, we cannot reduce the influence of atmospheric pressure on human health, but we can help our own body. The ability to measure atmospheric pressure, knowledge of folk signs, and the use of homemade instruments can help to properly organize your day, distribute time between work and rest.
Goal of the work: find out what role atmospheric pressure plays in human daily life.
Tasks:
- Study the history of atmospheric pressure measurement.
- Determine whether there is a connection between weather and atmospheric pressure.
- Study the types of instruments designed to measure atmospheric pressure, made by man.
- Study the physical phenomena underlying the operation of instruments for measuring atmospheric pressure.
- Dependence of liquid pressure on the height of the liquid column in liquid barometers.
Research methods
- Literature analysis.
- Summarizing the information received.
- Observations.
Field of study: Atmosphere pressure
Hypothesis: Atmospheric pressure is important for humans .
Significance of the work: the material of this work can be used in lessons and in extracurricular activities, in the lives of my classmates, students of our school, and all lovers of nature research.
Work plan
I. Theoretical part (information collection):
- Review and analysis of literature.
- Internet resources.
II. Practical part:
- observations;
- collecting weather information.
III. Final part:
- Conclusions.
- Presentation of work.
History of atmospheric pressure measurement
We live at the bottom of a huge ocean of air called the atmosphere. All changes that occur in the atmosphere certainly have an impact on a person, on his health, lifestyle, because... man is an integral part of nature. Each of the factors that determine the weather: atmospheric pressure, temperature, humidity, ozone and oxygen content in the air, radioactivity, magnetic storms, etc. has a direct or indirect effect on human well-being and health. Let's focus on atmospheric pressure.
Atmosphere pressure- this is the pressure of the atmosphere on all objects in it and the Earth's surface.
In 1640, the Grand Duke of Tuscany decided to build a fountain on the terrace of his palace and ordered water to be supplied from a nearby lake using a suction pump. The invited Florentine craftsmen said that this was impossible because the water had to be sucked up to a height of more than 32 feet (more than 10 meters). They could not explain why the water is not absorbed to such a height. The Duke asked the great Italian scientist Galileo Galilei to figure it out. Although the scientist was already old and sick and could not engage in experiments, he nevertheless suggested that the solution to the problem lay in the area of determining the weight of air and its pressure on the water surface of the lake. Galileo's student Evangelista Torricelli took up the task of resolving this issue. To test his teacher's hypothesis, he conducted his famous experiment. A glass tube 1 m long, sealed at one end, was completely filled with mercury, and tightly closing the open end of the tube, turned it over with this end into a cup with mercury. Some of the mercury poured out of the tube, some remained. An airless space formed above the mercury. The atmosphere presses on the mercury in the cup, the mercury in the tube also presses on the mercury in the cup, since equilibrium has been established, these pressures are equal. To calculate the pressure of mercury in a tube means to calculate the pressure of the atmosphere. If atmospheric pressure increases or decreases, the column of mercury in the tube increases or decreases accordingly. This is how the unit of measurement of atmospheric pressure appeared - mm. Hg Art. – millimeter of mercury. While observing the level of mercury in the tube, Torricelli noticed that the level was changing, which meant that it was not constant and depended on changes in the weather. If the pressure rises, the weather will be good: cold in winter, hot in summer. If the pressure drops sharply, it means that cloudiness and saturation of air with moisture are expected. A Torricelli tube with a ruler attached represents the first instrument for measuring atmospheric pressure - a mercury barometer. (Annex 1)
Other scientists also created barometers: Robert Hooke, Robert Boyle, Emil Marriott. Water barometers were designed by the French scientist Blaise Pascal and the German burgomaster of the city of Magdeburg, Otto von Guericke. The height of such a barometer was more than 10 meters.
To measure pressure, different units are used: mm of mercury, physical atmospheres, and in the SI system - Pascals.
Relationship between weather and atmospheric pressure
In Jules Verne's novel “The Fifteen-Year-Old Captain,” I was interested in the description of how to understand barometer readings.
“Captain Gul, a good meteorologist, taught him to understand the barometer readings. We will briefly tell you how to use this wonderful device.
- When, after a long period of good weather, the barometer begins to fall sharply and continuously, this is a sure sign of rain. However, if good weather lasts for a very long time, then the mercury column can drop for two or three days, and only after that any noticeable changes will occur in the atmosphere. In such cases, the more time passes between the start of the mercury fall and the start of rains, the longer the rainy weather will persist.
- On the contrary, if during a long period of rain the barometer begins to rise slowly but continuously, the onset of good weather can be confidently predicted. And good weather will remain the longer, the more time has passed between the beginning of the mercury rise and the first clear day.
- In both cases, a change in weather that occurs immediately after the rise or fall of the mercury column persists for a very short time.
- If the barometer rises slowly but continuously for two or three days or longer, this portends good weather, even if it has been raining non-stop all these days, and vice versa. But if the barometer rises slowly on rainy days, and immediately begins to fall when good weather comes, the good weather will not last long, and vice versa
- In spring and autumn, a sharp drop in the barometer foretells windy weather. In summer, in extreme heat, it predicts a thunderstorm. In winter, especially after prolonged frosts, a rapid drop in the mercury column indicates an upcoming change in wind direction, accompanied by thaw and rain. On the contrary, an increase in mercury during prolonged frosts foretells snowfall.
- Frequent fluctuations in the level of the mercury column, sometimes rising, sometimes falling, should in no case be considered as a sign of the approach of a long period; period of dry or rainy weather. Only a gradual and slow fall or rise in the mercury heralds the onset of a long period of stable weather.
- When, at the end of autumn, after a long period of wind and rain, the barometer begins to rise, this heralds a north wind at the onset of frost.
Here are the general conclusions that can be drawn from the readings of this valuable device. Dick Sand was an excellent judge of the barometer's predictions and was convinced many times how correct they were. Every day he consulted his barometer so as not to be taken by surprise by changes in the weather.”
I made observations of weather changes and atmospheric pressure. And I became convinced that this dependence exists.
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Instruments for measuring atmospheric pressure
For scientific and everyday purposes, you need to be able to measure atmospheric pressure. There are special devices for this - barometers. Normal atmospheric pressure is the pressure at sea level at a temperature of 15 °C. It is equal to 760 mm Hg. Art. We know that when the altitude changes by 12 meters, the atmospheric pressure changes by 1 mmHg. Art. Moreover, with increasing altitude, atmospheric pressure decreases, and with decreasing altitude, it increases.
The modern barometer is made liquidless. It's called an aneroid barometer. Metal barometers are less accurate, but not as bulky or fragile.
- a very sensitive device. For example, when climbing to the top floor of a nine-story building, due to differences in atmospheric pressure at different altitudes, we will find a decrease in atmospheric pressure by 2-3 mm Hg. Art.
A barometer can be used to determine the altitude of an aircraft. This barometer is called a barometric altimeter or altimeter. 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 a recorder - barograph.
(Storm Glass) (stormglass, Dutch. storm- "storm" and glass- “glass”) is a chemical or crystalline barometer consisting of a glass flask or ampoule filled with an alcohol solution in which camphor, ammonia and potassium nitrate are dissolved in certain proportions.
This chemical barometer was actively used during his sea voyages by the English hydrographer and meteorologist, Vice Admiral Robert Fitzroy, who carefully described the behavior of the barometer; this description is still used today. Therefore, stormglass is also called the "Fitzroy Barometer". From 1831–36, Fitzroy led the oceanographic expedition on HMS Beagle, which included Charles Darwin.
The barometer works as follows. The flask is hermetically sealed, but, nevertheless, the birth and disappearance of crystals constantly occurs in it. Depending on upcoming weather changes, crystals of various shapes form in the liquid. Stormglass is so sensitive that it can predict sudden weather changes 10 minutes in advance. The principle of operation has never received a complete scientific explanation. The barometer works better when located near a window, especially in reinforced concrete houses; probably in this case the barometer is not so shielded.
Baroscope– a device for monitoring changes in atmospheric pressure. You can make a baroscope with your own hands. To make a baroscope, the following equipment is required: A glass jar with a volume of 0.5 liters.
- A piece of film from a balloon.
- Rubber ring.
- Lightweight straw arrow.
- Wire for fastening the arrow.
- Vertical scale.
- Device body.
Dependence of liquid pressure on the height of the liquid column in liquid barometers
When atmospheric pressure changes in liquid barometers, the height of the liquid column (water or mercury) changes: when the pressure decreases, it decreases, when the pressure increases, it increases. This means that there is a dependence of the height of the liquid column on atmospheric pressure. But the liquid itself presses on the bottom and walls of the vessel.
The French scientist B. Pascal in the middle of the 17th century empirically established a law called Pascal's law:
Pressure in a liquid or gas is transmitted equally in all directions and does not depend on the orientation of the area on which it acts.
To illustrate Pascal's law, the figure shows a small rectangular prism immersed in a liquid. If we assume that the density of the prism material is equal to the density of the liquid, then the prism must be in a state of indifferent equilibrium in the liquid. This means that the pressure forces acting on the edge of the prism must be balanced. This will only happen if the pressures, i.e. the forces acting per unit surface area of each face, are the same: p 1 = p 2 = p 3 = p.
The pressure of the liquid on the bottom or side walls of the vessel depends on the height of the liquid column. Pressure force on the bottom of a cylindrical vessel of height h and base area S equal to the weight of a column of liquid mg, Where m = ρ ghS is the mass of the liquid in the vessel, ρ is the density of the liquid. Therefore p = ρ ghS / S
Same pressure at depth h in accordance with Pascal's law, the liquid also affects the side walls of the vessel. Liquid column pressure ρ gh called hydrostatic pressure.
Many devices that we encounter in life use the laws of liquid and gas pressure: communicating vessels, water supply, hydraulic press, sluices, fountains, artesian well, etc.
Conclusion
Atmospheric pressure is measured in order to more likely predict possible weather changes. There is a direct connection between pressure changes and weather changes. An increase or decrease in atmospheric pressure with some probability can serve as a sign of weather changes. You need to know: if the pressure drops, then cloudy, rainy weather is expected, but if it rises, dry weather is expected, with cold weather in winter. If the pressure drops very sharply, serious bad weather is possible: a storm, severe thunderstorm or storm.
Even in ancient times, doctors wrote about the influence of weather on the human body. In Tibetan medicine there is a mention: “joint pain increases in rainy times and during periods of high winds.” The famous alchemist and physician Paracelsus noted: “He who has studied the winds, lightning and weather knows the origin of diseases.”
In order for a person to be comfortable, the atmospheric pressure must be equal to 760 mm. Hg Art. If the atmospheric pressure deviates even by 10 mm in one direction or another, a person feels uncomfortable and this can affect his health. Adverse phenomena are observed during the period of changes in atmospheric pressure - increase (compression) and especially its decrease (decompression) to normal. The slower the change in pressure occurs, the better and without adverse consequences the human body adapts to it.
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Air pressure varies widely. If it is more than 760 millimeters of mercury, then it is considered elevated, if less, then reduced.
Observations of changes in atmospheric pressure make it possible to predict the weather. For example, when pressure increases in winter, the weather becomes frostier, and in summer it becomes hot. Low atmospheric pressure contributes to cloudiness and precipitation. Therefore, constantly knowing the value of atmospheric pressure and monitoring its changes is necessary not only for scientists and doctors, but for all of us.
Atmosphere pressure
Atmospheric pressure is measured in millimeters of mercury, as well as in Pascals and hectoPascals. Normal blood pressure is considered to be 760 mm Hg. Art. (1013.25 hPa) .
Atmospheric pressure generally changes with changes in weather conditions. Often, pressure drops before inclement weather and rises before good weather. Keeping records of pressure changes allows you to determine the movement of cyclones and the direction of winds.
A change in characteristic pressure often does not affect the well-being of a person living for a long time in a certain area. In cases where non-periodic fluctuations in atmospheric pressure occur, even healthy people experience headaches, decreased performance and a feeling of heaviness in the body.
Changes in atmospheric pressure also affect many technological processes. For example, when processing petroleum products, where pressure is one of the main controlled technical parameters; bakery production, where pressure readings greatly influence the moisture content of semi-finished dough products; in the aviation industry this is a very important parameter that affects the terms and conditions of operation.
Instruments for measuring atmospheric pressure
Today, there are several types of barometers that are used to measure air pressure:
- Mercury siphon barometer - represents a Y-shaped tube filled with mercury with an open and sealed end.
- Mercury cup barometer - consists of a vertical tube filled with mercury, the upper end of which is sealed, and the lower end is in a special cup with mercury.
- An aneroid barometer is an airless metal box with wavy walls.
- A barograph is a self-recording instrument that is used to monitor barometric pressure at certain periods of time.
- An electronic barometer is a digital device that operates on the principle of a conventional aneroid or on the principle of measuring air pressure on a sensitive crystal.
Mercury barometers are more accurate and reliable compared to aneroids; they are used to check the operation of other types of barometers. The height of pressure in them is determined by the height of the mercury column. Meteorological stations are equipped with cup barometers.
Measuring atmospheric pressure using a thermohygrometer
Atmospheric pressure is measured not only using various types of barometers, but also with such universal digital instruments as thermohygrometers. Despite the fact that the main task of these devices is to determine relative humidity and temperature, they also do an excellent job of measuring air pressure, showing the most accurate values. Therefore, such multifunctional devices are much more profitable to purchase than outdated barometers and psychrometers.
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All models of thermohygrometers have a communication interface with a PC via USB, RS-232 and can be mounted on a wall.
Devices control temperature and humidity air parameters:
thermometers– used to measure temperature;
barometers– used to measure pressure;
anemometers– used to measure wind speed;
psychrometers, hygrometers, moisture meters– used to measure humidity;
thermographs, barographs, hygrographs– are used to record changes in the corresponding parameters over time.
Scale measuring instrument, a set of marks and numbers on the instrument’s reference device, corresponding to a number of consecutive values of the measured quantity. Minimum part of the device division - value of division.
The following types are used thermometers:
Gas thermometer– the action is based on the dependence of pressure or gas volume on temperature.
Liquid thermometer– the action is based on the thermal expansion of the liquid. Depending on the temperature area of application, they are filled with ethyl alcohol (from –80 to +80 °C), mercury (from –35 to +750 °C) and other liquids.
Metal thermometer– the action is based on a change in the configuration of the bimetallic plate when heated due to the difference in the thermal expansion of the metals. Bimetallic plate - welded or riveted from strips of two different metals with different thermal expansion.
Resistance thermometer– the action is based on changes in the electrical resistance of metals and semiconductors with temperature.
Thermoelectric thermometer– the action is based on a change in the electromotive force in the thermocouple. Thermocouple consists of two series-connected (soldered) dissimilar conductors or semiconductors.
The following types are used arometers:
IN mercury (liquid) in a barometer, atmospheric pressure is measured by the height of the mercury column in a tube sealed at the top, lowered with the open end into a vessel with mercury. Mercury barometers- the most accurate instruments; meteorological stations are equipped with them and the operation of other types of barometers is checked using them.
Aneroid- a barometer in which atmospheric pressure is measured by the amount of deformation of an elastic metal box from which air has been pumped out. As pressure changes, the box contracts or expands, and an associated arrow moves along a scale to indicate the pressure.
Hypsothermometer (thermobarometer) is a device for measuring atmospheric pressure, based on the fact that with a change in pressure, the boiling point of water also changes. Used in expeditionary conditions in the mountains.
Wind speed measured with an anemometer.
Anemometer, a device for measuring wind speed and gas flows (sometimes wind direction - anemorumbometer) by the number of revolutions of a rotating turntable.
Measuring instruments humidity air have a common name moisture meters.
Moisture meter– a device for measuring the humidity of gases, liquids and solids (including granular) bodies. There are moisture meters: hygroscopic, electrochemical (for gases and liquids), hygrometric and psychrometric (for gases), capacitive and conductometric (for liquids and solids), as well as moisture meters based on the phenomenon of nuclear magnetic resonance.
Air humidity measured mainly by the following devices.
Hygrometer– a device for determining air humidity. The most common are the psychrometer and the hair hygrometer, which measure the relative humidity of the air by the change in the length of a fat-free human hair depending on the humidity of the air.
Psychrometer- a device for measuring temperature and air humidity, consisting of two thermometers, one of which (“wetted”) has a reservoir wrapped in wetted cambric. Temperature is determined by a “dry” thermometer, humidity - by the difference in readings of a dry and wet bulb thermometer.