How does a barometer work?

Question

I know that it has to do with air pressure but how does it measure the minute fluctuations in air pressure?

Answer 1

try puting a barometer in a clear bag and tie it. then squeze on the bag with a little presure and you will see it change just with a little pressure

Answer 2

When asking how does a barometer work; you must first understand what a barometer is. A barometer is an instrument used for measuring pressure in the atmosphere. Torricelli, a student of Galileo, created the barometer in the year 1644 in Florence.

Ordinarily a barometer is a glass tube 3 ft. long, filled with mercury, and inverted into a vessel also containing mercury. This causes the liquid in the tube to descend a few inches, leaving a vacuum at the top.

How a barometer works to measure the air pressure is; the pressure of all points in the same horizontal plane of a liquid being equal, the surface of the mercury, after the inversion of the tube cannot remain in one place when the atmosphere is pressing equally on both, but must rise when the air gets heavier and fall when the air gets lighter.

While a barometer can monitor changes in air pressure, sometimes you will not actually see a visible change in the weather. However, often monitoring your barometer and comparing it to the outside weather can help you be able to gauge what the weather will be like in the coming day; and you will begin to understand how changing weather can be predicted based on pressure changes in the atmosphere.

Low pressure (below 29.92) is associated with less stable weather patterns, while high pressure (above 29.92) is associated with more stable weather patterns. To forecast weather with your barometer, it is important to watch the speed and direction of barometric change. If the atmospheric pressure is very high, such as 30.30 you might think that stable weather is in store, but if the barometer were dropping rapidly, less stable weather would be predicted.

Answer 3

Water Barometer How It Works

Answer 4

In an original barometer, a sturdy glass tube about a meter long was filled with mercury, It was turned upside-down into a bath of mercury. The level of the mercury dropped quite a lot creating a vacuum on the top. The distance was measured from the surface of the mercury in the container to the level up the tube. It was noted that when the atmospheric pressure was high the distance was about 30.00 inches but when low it was only 28.00inches therefore it was measuring the atmospheric pressure.
A later device was developed known as an Aneroid which consisted of a flat corrugated box partially evacuated of air and connected by a lever to a dial and pointer suitably marked.
This type is the one that most are familiar with.
To change from inches to millimeters multiply by 25.4
To change from millimeters to millibars multiply by one and a third

Answer 5

there are numerous types of barometers:

The link below is a good place to start.

Water-based barometers
This concept of "decreasing pressure means bad weather" is the basis for a primitive weather prediction device called a weather glass or thunder glass. It can also be called a "storm glass" or a "Goethe thermometer" (the writer Goethe popularized it in Germany).

It consists of a glass container with a wide spout. The container is filled with water up to about the middle of the spout; some air is left in the main body of the container. The design is such that when the air pressure decreases, the pressure of the air pocket inside the device will push some of the water up the spout. If the air pressure is low enough, some of the water may even drip out of the spout. These devices are essentially a water-based version of the mercury barometer. The "Thunder Glass" is extremely susceptible to the ambient temperature which will alter the height of the water column in the spout.

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Mercury barometers
A standard mercury barometer has a glass column of about 30 inches (about 76 cm) in height, closed at one end, with an open mercury-filled reservoir at the base. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more downward force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the downward force placed on the reservoir.

The first barometer of this type was devised in 1643 by Evangelista Torricelli. Torricelli had set out to create an instrument to measure the weight of air, or air pressure, and to study the nature of vacuums. He used mercury, perhaps on a suggestion from Galileo Galilei, because it is significantly denser than water. To create a vacuum with water takes a column over 30 feet long, while with mercury it takes less than four feet.

Torricelli documented that the height of the mercury in a barometer changed slightly each day and concluded that this was due to the changing pressure in the atmosphere. He wrote: "We live submerged at the bottom of an ocean of elementary air, which is known by incontestable experiments to have weight".

The mercury barometer's design gives rise to the expression of atmospheric pressure in inches or millibars: the pressure is quoted as the level of the mercury's height in the vertical column. 1 atmosphere is equivalent to about 29.9 inches, or 760 millimeters, of mercury. The use of this unit is still popular in the United States, although it has been disused in favor of SI or metric units in other parts of the world. Barometers of this type can usually measure atmospheric pressures in the range between 28 and 31 inches of mercury.

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Aneroid barometers

photo of an old aneroid barometerAnother type of barometer, the aneroid barometer, uses a small, flexible metal box called an aneroid cell. The box is tightly sealed after some of the air is removed, so that small changes in external air pressure cause the cell to expand or contract. This expansion and contraction drives a series of mechanical levers and other devices which are displayed on the face of the aneroid barometer.

It is often necessary to tap this type of barometer before reading it. This loosens the needle and causes the reading to jump in the direction of the most recent changes in pressure.

A simple aneroid barometer can be made using a latex membrane from a glove or balloon stretched over the mouth of a bottle and held in place with a rubber band. Taping one end of a long thin stick or piece of spaghetti to the center of the membrane provides an indicator needle, amplifying small motions of the membrane at the other end of the stick.

Answer 6

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Answer 7

Barometer




2 items
Barometer, instrument for measuring atmospheric pressure, that is, the force exerted on a surface of unit area by the weight of the atmosphere. Because this force is transmitted equally in all directions through any fluid, it is most easily measured by observing the height of a column of liquid that, by its weight, exactly balances the weight of the atmosphere. A water barometer is far too large to be used conveniently. Liquid mercury, however, is 13.6 times as heavy as water, and the column of mercury sustained by normal atmospheric pressure is only about 760 mm (about 30 in) high.

Normal, or standard, atmospheric pressure is usually defined at 1013.25 millibars, which is equivalent to 760 mm (29.9213 in) of mercury or 1.03323 kg/sq cm (14.6960 lb/sq in).

An ordinary mercury barometer consists of a glass tube about 840 mm (about 33 in) high, closed at the upper end and open at the lower. When the tube is filled with mercury and the open end placed in a cup full of the same liquid, the level in the tube falls to a height of about 760 mm (about 30 in) above the level in the cup, leaving an almost perfect vacuum at the top of the tube. Variations in atmospheric pressure cause the liquid in the tube to rise or fall by small amounts, rarely below 737 mm (29 in) or above 775 mm (30.5 in) at sea level. When the mercury level is read with a form of gradated scale, known as a vernier attachment, and suitable corrections are made for altitude and latitude (because of the change of gravity), for temperature (because of the expansion or contraction of the mercury), and for the diameter of the tube (because of capillarity), the reading of a mercury barometer is reliable to within 0.1 mm (0.004 in).

A more convenient form of barometer (and one that is almost as accurate) is the aneroid, in which atmospheric pressure bends the elastic top of a partially evacuated drum, actuating a pointer. A suitable aneroid barometer is often used as an altimeter (instrument measuring altitude), because pressure decreases rapidly with increasing altitude (about 25 mm/1 in. of mercury per 305 m/1000 ft at low altitudes).

Answer 8

It uses a large diaphragm or bellows sealed with a known amount of gas inside. The pressure on the outside of the bellows, which is atmospheric pressure, is compared to the constant pressure inside the bellows. For example, as the atmospheric pressure drops, the pressure inside the bellows will be greater that the pressure on the outside and the bellows must expand slightly to equalize the pressures. As it expands, it moves the needle to a lower number on the scale.

Answer 9

Liquid barometers

Water-based barometers
This concept of "decreasing pressure means bad weather" is the basis for a primitive weather prediction device called a weather glass or thunder glass. It can also be called a "storm glass" or a "Goethe thermometer" (the writer Goethe popularized it in Germany).

It consists of a glass container with a WIDE spout. The container is filled with water up to about the middle of the spout; some air is left in the main body of the container. The design is such that when the air pressure decreases, the pressure of the air pocket inside the device will push some of the water up the spout. If the air pressure is low enough, some of the water may even drip out of the spout. These devices are essentially a water-based version of the mercury barometer. The "Thunder Glass" is extremely susceptible to the ambient temperature which will alter the height of the water column in the spout.


Mercury barometers
A standard mercury barometer has a glass column of about 30 inches (about 76 cm) in height, closed at one end, with an open mercury-filled reservoir at the base. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more downward force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the downward force placed on the reservoir.

The first barometer of this type was devised by Evangelista Torricelli, a student of Galileo Galilei, in 1643. Torricelli had set out to create a perfect vacuum, and an instrument to measure air pressure. He succeeded in creating a vacuum in the top of a tube of mercury. Torricelli also noticed that the level of the fluid in the tube changed slightly each day and concluded that this was due to the changing pressure in the atmosphere. He wrote: "We live submerged at the bottom of an ocean of elementary air, which is known by incontestable experiments to have weight".

The mercury barometer's design gives rise to the expression of atmospheric pressure in inches or millibars: the pressure is quoted as the level of the mercury's height in the vertical column. 1 atmosphere is equivalent to about 29.9 inches, or 760 millimeters, of mercury. The use of this unit is still popular in the United States, although it has been disused in favor of SI or metric units in other parts of the world. Barometers of this type can usually measure atmospheric pressures in the range between 28 and 31 inches of mercury.


photo of an old aneroid barometer
Aneroid barometers
Another type of barometer, the aneroid barometer, uses a small, flexible metal box called an aneroid cell. The box is tightly sealed after some of the air is removed, so that small changes in external air pressure cause the cell to expand or contract. This expansion and contraction drives a series of mechanical levers and other devices which are displayed on the face of the aneroid barometer.

A simple aneroid barometer can be made using a latex membrane from a glove or balloon stretched over the mouth of a bottle and held in place with a rubber band. Taping one end of a long thin stick or piece of spaghetti to the center of the membrane provides an indicator needle, amplifying small motions of the membrane at the other end of the stick.


Applications
A barometer is commonly used for weather prediction, as high air pressure in a region indicates fair weather while low pressure indicates that storms are more likely. Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced. Isobars drawn on such a map links sites with the same pressure and give, in effect, a contour maps of areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Low atmospheric pressure, on the other hand, represents the path of least resistance for a weather system, making it more likely that low pressure will be associated with increased storm activities.


Compensations

Temperature
The density of mercury will change with temperature, so a reading must be adjusted for the temperature of the instrument. For this purpose a mercury thermometer is usually mounted on the instrument. No such compensation is required for an aneroid barometer.


Altitude
As the air pressure will be reduced at altitudes above sea level (and increased below sea level) the actual reading of the instrument will be dependent upon its location. This pressure is then converted to an equivalent sea-level pressure for purposes of reporting and for adjusting aircraft altimeters (as aircraft may fly between regions of varying normalized atmospheric pressure owing to the presence of weather systems). Aneroid barometers have a mechanical adjustment for altitude that allows the equivalent sea level pressure to be read directly and without further adjustment if the instrument is not moved to a different altitude.

Answer 10

by being able to measure the psi of the air and with the very sensitive air pressure meter i forget what it is called sorry hope that this will help...