CHAPTER 3 THE ATMOSPHERE
LESSON 2 AIR PRESSURE
Air has mass, and also has density and pressure.
Density = D = Mass = M
Volume V
Density - the amount of mass in a given volume.
The greater the number of air molecules = the greater the density
The lower the number of air molecules = the lower the density
Pressure- a force applied to an area
Air pressure- caused by the weight of air pushing on an area
The air pressure at sea level is 14.7 lbs. per square inch.
MEASURING AIR PRESSURE
Barometer – an instrument used to measure air pressure
1. Mercury Barometer
 a long glass tube closed at one end and open at other
 closed end is almost a vacuum
 as air pushes down the level goes up
2. Aneroid Barometer
“without liquid” an air tight metal chamber that is sensitive
to changes in air pressure
WEATHER REPORTS
Forecasts- “uses inches of mercury”
Maps- use millibars 1 inch of mercury = 33.86 millibars (ex; 980 mb)
AIR PRESSURE AND ALTITUDE
Altitude – the distance above sea level
Air pressure decreases as you move further from the Earth’s surface
(the air spreads out), so the density goes down
Air pressure increases as you move closer to the Earth’s surface (the air
molecules are closer), so the density goes up
Cold air = more dense = higher air pressure
Warm air = less dense = lower air pressure