What is a Barometer?
Barometer is an instrument that measures atmospheric pressure, used in particular for weather forecasting and altitude determination. Weather instruments that calculate atmospheric pressure (also known as air pressure or barometric pressure)—the weight of air in the atmosphere is commonly used. This is where pressure would be the lowest: at sea level; above Mt. Everest; at the bottom of the Grand Canyon and above a skyscraper.
How does a Barometer Work?
The plastic wrap is driven by high atmospheric pressure, causing it to cave in. The plastic and straw sink taped segment causing tilt-up of the end of the straw. When the ambient pressure is low, the air pressure inside the can will be higher. The plastic wrap bulges out, elevating the straw's wrapped edge. The tip of the straw falls to the bottom of the jar until it comes to rest. Temperature also affects atmospheric pressure so you need a constant temperature for your barometer to be accurate. Keep it away from a window or other locations where temperature changes are experienced.
Types of Barometer
There are two different types of barometer that work differently to measure the atmospheric pressure.
Mercury Barometer
Aneroid Barometer
Mercury Barometer
Torricelli invented the weather instrument in 1643. A mercury barometer is a column of glass marked in inches away. The glass tube's top end is closed, and the other end sits in a small cup of mercury called a cistern. Inside the upright glass tube lies a column of mercury. In physics classes Mercury barometers are often used today.
How Mercury Barometers Work
A mercury barometer, which is the mean barometric pressure at sea level, would give a typical mercury reading at around 29 inches. At the time of a hurricane, the atmospheric pressure to the cistern is less. The barometer in turn displays the drop in mercury levels. As the storm passes, a high - pressure system replaces low atmospheric pressure, which increases mercury levels in the column of mercury.
The simplest type of barometer is a big, closed tube that stands upside down in a mercury bath (a thick liquid metal at room temperature) so that the liquid partially rises up the tube a little like it does in a thermometer. In barometers, we use mercury, because it is more convenient than using gas. Water is less dense (less heavy, in effect) than mercury so air pressure lifts a certain volume of water up a tube far higher than that of mercury. In other words, if you're using water, you need a really tall tube and your barometer is going to be so large as to be impractical. But you can get away with a much smaller piece of equipment if you use mercury
A piece of apparatus such as this is called a Torricellian barometer after Italian mathematician Evangelista Torricelli (1608–1647), a pupil of Galileo's, who invented the first such instrument in 1643. He took a long tube of glass, sealed at one end, filled it from a bowl of mercury, put his finger over the open end, turned it upside down, and stood it upright in the bowl of mercury. Since he was careful not to let any air into the tube, there was a vacuum in the space that developed above the mercury column. Indeed, this was the first time anyone in a laboratory had ever created a vacuum (and a vacuum made that way is called a Torricellian vacuum in honor of its inventor).
Around sea level, the atmosphere will force down a pool of mercury and make it rise in a tube to about 760mm (about 30in) in height.
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Aneroid Barometer
A fluidless aneroid barometer is developed. It consists of a small, flexible metal box called an aneroid capsule, made from a beryllium and copper alloy. The metal box is tightly sealed so that changes in atmospheric pressure outside of the box allow the levers and springs inside the box to expand and contract.
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What is a Barometer used for?
The barometers were mainly used to measure patterns of weather. When used in combination with wind observations, barometers can provide considerably accurate weather forecasts for the short term.
They are also used to measure an aircraft's speed by checking the air moving pressure against the aircraft. They also serve as indicators of altimeter settings for providing aircraft altimeter altitude information.
They also play a significant role in improving the accuracy of missile and satellite tracking systems by measuring the humidity conditions that would impede satellite and missile flight.
FAQs on How to Make A Barometer?
1. What is a barometer and on what fundamental principle does it operate?
A barometer is a scientific instrument designed to measure atmospheric pressure. Its operation is based on the principle that the weight of the air in the atmosphere exerts pressure on a surface. Changes in this pressure, indicated by the barometer, help in forecasting weather and determining altitude.
2. What materials are needed to create a simple barometer at home?
To build a basic aneroid-style barometer, you can use common household items. You will need:
- A glass jar or a can with a wide mouth.
- A balloon or a piece of plastic wrap.
- A rubber band or tape to seal the balloon or wrap.
- A drinking straw to act as a pointer.
- Glue or tape to attach the straw.
- A piece of paper or cardboard to create a measurement scale.
3. How does a homemade bottle or jar barometer indicate changes in air pressure?
In a homemade jar barometer, air is trapped inside the sealed jar at a certain pressure. When the outside atmospheric pressure increases (a high-pressure system, often indicating fair weather), it pushes down on the balloon or plastic wrap, causing the attached straw to tilt upwards. Conversely, when the outside pressure drops (a low-pressure system, indicating possible storms), the higher pressure inside the jar pushes the wrap outwards, causing the straw to tilt downwards.
4. Why is mercury traditionally used in barometers instead of a more common liquid like water?
Mercury is used due to its very high density. Standard atmospheric pressure can support a column of water nearly 10 meters (34 feet) high, which would require an impractically large instrument. Because mercury is 13.6 times denser than water, the same atmospheric pressure supports a much smaller column of mercury, about 760 mm (30 inches). This allows for a much more compact and manageable barometer design.
5. What is the main difference between a mercury barometer and an aneroid barometer?
The primary difference lies in their mechanism. A mercury barometer uses a column of liquid mercury in a glass tube to measure air pressure by balancing its weight against the atmosphere. An aneroid barometer, which means 'without fluid', uses a flexible, sealed metal cell. Changes in external air pressure cause this cell to expand or contract, and this mechanical movement is amplified by levers to move a needle on a dial. Aneroid barometers are generally more portable and safer.
6. What is the significance of the vacuum created above the mercury in a Torricellian barometer?
The space at the top of the sealed tube in a mercury barometer is a near-perfect vacuum known as a Torricellian vacuum. Its presence is crucial because it ensures there is no air pressure from trapped gas pushing down on the mercury column from inside. This allows the height of the mercury column to be a direct and accurate measure of the external atmospheric pressure alone.
7. How can a falling barometer reading be used to predict an approaching storm?
A falling barometer reading indicates that atmospheric pressure is decreasing. This is a strong sign of an approaching low-pressure system, which displaces the heavier, high-pressure air. These low-pressure systems are typically associated with unstable weather conditions like clouds, strong winds, and precipitation. A rapid drop in pressure often signals the imminent arrival of a storm.
