How Barometers Work
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What are Barometers?
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Barometers are instruments used to measure atmospheric pressure. Atmospheric pressure, which is the weight of the air in the atmosphere, is used to predict weather patterns. Weather patterns are accompanied by bands of high and low atmospheric pressure, so a rise or drop in pressure can indicate a change in conditions. There are two main types of barometers. The classic, more widely available type is the mercury barometer, while the newer, digital type is called an aneroid barometer. Though the barometers function slightly differently, both yield similar results.
Mercury Barometer
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A mercury barometer is usually a glass, mercury-filled tube that's sealed on one end. The open end of the tube sits in a plate, known as the reservoir, that's also filled with mercury. Mercury barometers measure atmospheric pressure by balancing the weight of the mercury against the weight of the air around it. The empty part of the tube creates a vacuum effect. This effect sucks the mercury up in the tube when the weight of the mercury is less than that of the atmospheric pressure around it. When the mercury weighs more than the atmospheric pressure, the mercury level in the tube drops.
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Aneroid Barometer
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Aneroid barometers are digital instruments that measure atmospheric pressure with electrical charges. These barometers start out as sealed discs or capsules that are made of a thin sheet of metal. The metal object has two small metallic strips running up either side of its interior, and the strips of metal are connected by a single electrical current. As the air pressure around the metal increases and decreases, the metal contracts and expands accordingly. When the metal contracts and expands, the distance between the two metallic strips (and the length of the connecting electrical current) changes accordingly. The barometer measures the length of the electrical charge and calculates the atmospheric pressure based of off that reading.
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