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A barometer is a device for measuring atmospheric pressure.The common atmospheric pressure at sea level is 1 environment car accessories, which is the pressure that will support a column of mercury 760mm (29.92 inches) higher suzuki parts, i.e., about 1Kg/cm2 (14.71 1b./in2 ). This would correspond to the pressure exerted by a column of air about five miles (8 Km) high if its density have been constant and equal to that at sea level.This explains why the barometric pressure on the top of a mountain is, say, 10,000 ft. (3000m) higher, the column of air pressing down at the leading is only about three miles (assuming continual density).

Really the atmospheric pressure at any distinct altitude is in no way constant, but varies by reasonably small amounts about the common.These variations give information for climate forecasts. When a rubber suction pad is pressed against a smooth wall, it will stay adhering to the wall. By pressing the pad down flat against the wall surface the air is expelled from the cavity below the pad and a vacuum is formed there.

The air pressure which initially acted in that cavity now no longer thrusts against the inside of the pad. When the latter is released, it will remain in the compressed position because the air pressure acts on the outside only and therefore presses the edge of the pad down so firmly that no air will penetrate into the cavity, which therefore remains void of air.

The external air pressure therefore keeps the suction pad firmly pressed against the wall. Difference of air pressure is also utilised when we drink a liquid by means of a straw. Air is sucked out of the straw , and the barometric air pressure, which acts upon the surface of the liquid in the glass, will force the liquid up via the straw.

If a lengthy glass tube, which is sealed at one particular end and open at the other, is filled with mercury and is then stood upright, with the open finish downwards, in a dish containing mercury, then so much mercury will flow out of the tube until a column of mercury not a lot more than 760 mm in height above the mercury surface in the dish remains. The air pressure which acts upon the surface of the mercury in the dish is as a result capable to hold up a 760 mm higher mercury column.

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Topic revision: r1 - 2013-03-12 - 15:28:04 - AnnabEll732
 
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