Unit: Water and the Atmosphere

Lesson 2: Air Pressure

Essential Questions:1.) What are some properties of air?

2.) What instruments measure air pressure?

3.) How does altitude affect air pressure and density?

High-altitude pilots who fly above 15,250 meters are in a zone with conditions similar to deep space. At these heights, air pressure is so low that blood can boil. A pilot can also pass out in less than a minute from lack of oxygen. To survive, pilots wear pressure suits. They inflate in an emergency, keeping air pressure stable for the pilot. The suits are “very, very restrictive,” says pilot David Wright. “But it saves your life, so you’re able to put up with that.”

Do Now

Properties of Air

• Mass

• Density

• Air pressure

The air above you going up through the atmosphere is called an air column.

The molecules in the air push in all directions.

Instruments

An instrument that barometeris used to measureair pressure

Mercury Barometer

When air pressure increases, it presses down more on the mercury and the column rises.

Aneroid Barometer

When air pressure increases, the walls push in. When it decreases, the walls bulge out. The needle moves.

Distance above altitudesea level

As altitude increases, air pressure and density decrease.