Air Pressure

1
Air Pressure

• Ch 15 Sec. 3
• ByIrma Krupic
• T-3

2
Contents

• Guide for reading
• Properties of air
• Measuring air pressure

3
Properties of Air

• Atoms,mass,molecules, density,pressure.
• Densityamount 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.
• Force pushing on an area is pressure.

• Denser substancemore 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 barometersaneroid barometers are
• used to measure changes in air pressure.
• Falling air pressurestorm is coming.
• Rising air pressureweather is clearing.

5
Mercury Barometer

• 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.

6
Aneroid Barometer

• 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.
• Chamber is connected to dial be series of springs
  levers.When shape of chamber changes needle on
  dial moves.

7
Units of Air Pressure

• Inches of mercury.
• National weather service maps use millibars to
  measure air pressure.
• One inch of mercury 33.87 millibars.
• 30 inches of mercury1016 millibars.

8
Increasing Altitude

• Air pressure at the top of mount McKinley is more
  than 6 kilometers above sea level, thats 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.

9
Altitude Affects Density

• Air pressure is greatest at sea level.
• 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.

10
Web Resources

• http//www.grc.nasa.gov/WWW/K-12/airplane/pressure
  .html
• http//kids.earth.nasa.gov/archive/air_pressure/