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Weather

Weather. Part 2: Air Pressure. Air Pressure…. is a measure of the force of the air pressing down on Earth’s surface. a t any point on the Earth is equal to the weight of the air directly above that point. at any point on Earth depends on the density of the air. Video: Air Pressure Explained.

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Weather

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  1. Weather Part 2: Air Pressure

  2. Air Pressure… • is a measure of the force of the air pressing down on Earth’s surface. • at any point on the Earth is equal to the weight of the air directly above that point. • at any point on Earth depends on the density of the air. • Video: Air Pressure Explained

  3. Factors that Affect Air Pressure Temperature • Temp. = Air Pressure • Temp. = Air Pressure Elevation (Altitude) • Altitude = Density = Air Pressure Water Vapor • Because the mass of H2O is less than the mass of O2 and N2,increasing water vapor causes a decrease in density and therefore a decrease in air pressure • Water Vapor=  Air Pressure

  4. Measuring Air Pressure Barometer: an instrument used to measure air pressure Two types: Mercury and Aneroid Standard air pressure is measured at 0°C at sea level. (FYI: 1 atmosphere = 29.92 in Hg = 14.7 psi = 101,325 Pa = 1,013.25mb = 1.013 bar) 1Pascal (Pa)= 1 N/m2

  5. Mercury Barometers • Invented 1643 by Evangelista Torricelli • Glass tube closed at one end and filled with mercury • Open end put in container of mercury • The column of Hg changes height with changes in air pressure

  6. Aneroid Barometer • Airtight metal box with air removed • Needle moves across dial as air pressure changes

  7. Air Pressure and Weather • High pressure generally means fair weather • High pressure occurs when large air masses come together in the upper atmosphere. • The air presses down on layers below and blocks warm, moist air from rising, so clouds do not form. • Low pressure generally leads to cloudy, rainy weather • Low pressure occurs when large air masses move apart in the upper atmosphere. • This allows warm, moist air to rise and form clouds.

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