1. Air Pressure Ch 15 Sec. 3 By:Irma Krupic T-3

2. Contents Contents Guide for reading Guide for reading Properties of air Properties of air Measuring air pressure Measuring air pressure

3. Properties of Air Properties of Air Atoms,mass,molecules, density,pressure. Atoms,mass,molecules, density,pressure. Density:amount of mass in a given volume of air. Density:amount of mass in a given volume of air. The more molecules in a given volume of air the higher the density.Fewer molecules =low density. The more molecules in a given volume of air the higher the density.Fewer molecules =low density. Force pushing on an area is pressure. Force pushing on an area is pressure. Denser substance=more mass per unit volume than a less dense one. Air pressure: weight of a column of air pushing down on an area.Molecules in air push in all directions.

4. Instrument Used to Measure Air Pressure Mercury barometers+aneroid barometers are Mercury barometers+aneroid barometers are used to measure changes in air pressure. Falling air pressure=storm is coming. Falling air pressure=storm is coming. Rising air pressure=weather is clearing. Rising air pressure=weather is clearing.

5. Mercury Barometer Mercury Barometer Was the first barometer invented. Was the first barometer invented. Glass tube open at bottom. Partially filled with mercury. Space above the mercury has no air.Open end of tube is in a dish of mercury.Air pressure pushing down on surface of mercury in dish is equal to weight of column in the tube. When air pressure increases,it presses down more on the mercury. Greater air pressure makes the column of mercury higher. Glass tube open at bottom. Partially filled with mercury. Space above the mercury has no air.Open end of tube is in a dish of mercury.Air pressure pushing down on surface of mercury in dish is equal to weight of column in the tube. When air pressure increases,it presses down more on the mercury. Greater air pressure makes the column of mercury higher.

6. Aneroid Barometer Aneroid Barometer Has airtight metal chamber,metal chamber is sensitive to changes in air pressure. Has airtight metal chamber,metal chamber is sensitive to changes in air pressure. As air pressure increases,thin walls of chamber push in. As pressure drops,walls come out. As air pressure increases,thin walls of chamber push in. As pressure drops,walls come out. Chamber is connected to dial be series of springs +levers.When shape of chamber changes needle on dial moves. Chamber is connected to dial be series of springs +levers.When shape of chamber changes needle on dial moves.

7. Units of Air Pressure Units of Air Pressure Inches of mercury. Inches of mercury. National weather service maps use millibars to measure air pressure. National weather service maps use millibars to measure air pressure. One inch of mercury =33.87 millibars. One inch of mercury =33.87 millibars. 30 inches of mercury=1016 millibars. 30 inches of mercury=1016 millibars.

8. Increasing Altitude Increasing Altitude Air pressure at the top of mount McKinley is more than 6 kilometers above sea level, that’s less than half the air pressure above sea level. Air pressure at the top of mount McKinley is more than 6 kilometers above sea level, that’s less than half the air pressure above sea level. Altitude-distance above sea level.Air pressure decreases as altitude increases. When air pressure decreases,so does density. Altitude-distance above sea level.Air pressure decreases as altitude increases. When air pressure decreases,so does density.

9. Altitude Affects Density Altitude Affects Density Air pressure is greatest at sea level. Air pressure is greatest at sea level. Near the top of the atmosphere it has less weight pressing on it. Near the top of the atmosphere it has less weight pressing on it. As you go up through the atmosphere, air pressure decreases, and as air pressure decreases,the density of air decreases too. As you go up through the atmosphere, air pressure decreases, and as air pressure decreases,the density of air decreases too.

10. Web Resources Web Resources http://www.grc.nasa.gov/WWW/K- 12/airplane/pressure.html http://www.grc.nasa.gov/WWW/K- 12/airplane/pressure.html http://www.grc.nasa.gov/WWW/K- 12/airplane/pressure.html http://www.grc.nasa.gov/WWW/K- 12/airplane/pressure.html http://kids.earth.nasa.gov/archive/air_p ressure/ http://kids.earth.nasa.gov/archive/air_p ressure/ http://kids.earth.nasa.gov/archive/air_p ressure/ http://kids.earth.nasa.gov/archive/air_p ressure/