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.
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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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.