what are the uses of a barometer ( need more than 10)
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It’s very simple; the atmosphere above us weight about one kilo per square centimetre! … can you feel about one kilo (2 lbs) on your extended finger (of about a square cm?)
No, because air is a fluid and presses from all directions, also from under. To measure that pressure you should remove the air under your finger and that is not easy! One way to do it is to use a tube filled with a fluid like, water, open at one end and closed at the other. When it forms vacuum at the closed end, then the pressure of the water at the open end equals the air pressure.
The problem is that … the tube should be ten meters high. (incidentally, this is why a suction pump can’t pump water higher than ten meters)
We then use the heaviest fluid we know of, mercury. With mercury the tube can be reduced to 760 mm (29.9 inches) and that is a bit more convenient in our homes! ;-)
The aneroid barometer is made of a vacuum box with a surface connected to a dial. As the atmospheric pressure changes, the surface moves and that moves the arrow of a dial. The thing is, it has to be calibrated to be of any value. But, temperature changes the density of the air so, all barometers (and all professional instruments) are calibrated for the so-called International Standard Atmosphere (ISA) that defines the air to be dry, the temperature 15 degrees Celsius (the average at sea level on earth) and the adiabatic lapse rate (how cold it gets with altitude) to be 0.65 C per 100 meters.
At home, you can have a mercury barometer. But if you want to measure pressure over time, you need a barograph which makes the “needle” of an aneroid barometer to move with a pen writing on a paper the present pressure.
That was popular in ships as e.g. a fall or rise of ten millibars (today called hPa - hecto-Pascal) in a period of eight hours, was a sure sign that a gale force wind was on its way. Of course, today, the barograph use a digital recording.
Another typical use of the aneroid barometer is, the altimeter that I have in my aircraft. In aviation, altitude is measured as a difference of pressure. Of course, you must first adjust your altimeter to the present pressure at your airfield. This is called, the QNH. When you fly, different air traffic controllers will give you the local QNH so that your altimeter is always correct and correspond to the altitude they see on their radar. The thing is; if you fly from, say, a high pressure towards a lower one without adjusting your QNH, you will fly lower than indicated.
No, because air is a fluid and presses from all directions, also from under. To measure that pressure you should remove the air under your finger and that is not easy! One way to do it is to use a tube filled with a fluid like, water, open at one end and closed at the other. When it forms vacuum at the closed end, then the pressure of the water at the open end equals the air pressure.
The problem is that … the tube should be ten meters high. (incidentally, this is why a suction pump can’t pump water higher than ten meters)
We then use the heaviest fluid we know of, mercury. With mercury the tube can be reduced to 760 mm (29.9 inches) and that is a bit more convenient in our homes! ;-)
The aneroid barometer is made of a vacuum box with a surface connected to a dial. As the atmospheric pressure changes, the surface moves and that moves the arrow of a dial. The thing is, it has to be calibrated to be of any value. But, temperature changes the density of the air so, all barometers (and all professional instruments) are calibrated for the so-called International Standard Atmosphere (ISA) that defines the air to be dry, the temperature 15 degrees Celsius (the average at sea level on earth) and the adiabatic lapse rate (how cold it gets with altitude) to be 0.65 C per 100 meters.
At home, you can have a mercury barometer. But if you want to measure pressure over time, you need a barograph which makes the “needle” of an aneroid barometer to move with a pen writing on a paper the present pressure.
That was popular in ships as e.g. a fall or rise of ten millibars (today called hPa - hecto-Pascal) in a period of eight hours, was a sure sign that a gale force wind was on its way. Of course, today, the barograph use a digital recording.
Another typical use of the aneroid barometer is, the altimeter that I have in my aircraft. In aviation, altitude is measured as a difference of pressure. Of course, you must first adjust your altimeter to the present pressure at your airfield. This is called, the QNH. When you fly, different air traffic controllers will give you the local QNH so that your altimeter is always correct and correspond to the altitude they see on their radar. The thing is; if you fly from, say, a high pressure towards a lower one without adjusting your QNH, you will fly lower than indicated.
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