MetcalfeEnglert191

A barometer is a device for measuring atmospheric pressure.The average atmospheric pressure at sea level is 1 atmosphere, which is the pressure that will support a column of mercury 760mm (29.92 inches) higher, 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) higher if its density had been continuous and equal to that at sea level.This explains why the barometric pressure on the leading of a mountain is, say, ten,000 ft. (3000m) higher, the column of air pressing down at the best is only about three miles (assuming continuous density).

In fact the atmospheric pressure at any distinct altitude is in no way constant, but varies by relatively small amounts about the typical.These variations give information for climate forecasts. When a rubber suction pad is pressed against a smooth wall, it will remain adhering to the wall. By pressing the pad down flat against the wall surface the air is expelled from the cavity under 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 stay in the compressed position because the air pressure acts on the outside only and hence presses the edge of the pad down so firmly that no air will penetrate into the cavity, which as a result remains void of air.

The external air pressure hence keeps the suction pad firmly pressed against the wall. Distinction 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 by means of the straw.

If a extended glass tube, which is sealed at a single finish 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 a lot mercury will flow out of the tube till a column of mercury not far 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 in a position to hold up a 760 mm high mercury column. volkswagen accessories