# Pressur1 - -2 called a pascal 1Pa = 1 N/m 2 • The...

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Pressure The most readily measured properties of a gas are: Temperature Volume Pressure Pressure (P) is the force (F) which acts on a given area (A) The gas in an inflated balloon exerts a pressure on the inside surface of the balloon Atmospheric Pressure and the Barometer Due to gravity, the atmosphere exerts a downward force and therefore a pressure upon the earth's surface Force = (mass*acceleration) or F=ma The earth's gravity exerts an acceleration of 9.8 m/s 2 A column of air 1 m 2 in cross section, extending through the atmosphere, has a mass of roughly 10,000 kg ( one Newton equals 1 kg m/s 2 )

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The force exerted by this column of air is approximately 1 x 10 5 Newtons The pressure, P , exerted by the column is the force, F , divided by its cross sectional area, A : The SI unit of pressure is Nm
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Unformatted text preview: -2 , called a pascal ( 1Pa = 1 N/m 2 ) • The atmospheric pressure at sea level is about 100 kPa Atmospheric pressure can be measured by using a barometer • A glass tube with a length somewhat longer than 760 mm is closed at one end and filled with mercury • The filled tube is inverted over a dish of mercury such that no air enters the tube • Some of the mercury flows out of the tube, but a column of mercury remains in the tube. The space at the top of the tube is essentially a vacuum • The dish is open to the atmosphere, and the fluctuating pressure of the atmosphere will change the height of the mercury in the tube The mercury is pushed up the tube until the pressure due to the mass of the mercury in the column balances the atmospheric pressure...
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