Bell Question: Using the captions to help you, explain why one of these containers was deformed.Picture 1: The Pringles can I packed from home is bulging. (In Yellowstone National Park, Elevation = ~9,000ft.)

Picture 2: The bottle I left in the car is crushed. (At airport, Elevation = 0ft, coming home from Sequoia National Park, Elevation = ~7500ft)

What is pressure?• Amount of force in a given area – Particles push

against each other to create a force• Atmospheric Pressure = Weight of air as it

pushes down on Earth’s surface (density)• Atmospheric gases held in place by gravity

Why isn’t air pressure the same everywhere?

• Pressure increases as you move deeper into the air

• Deepest point = EARTH’S SURFACE!!

How do we measure pressure?

• A barometer measures inches of mercury or millibars

A standard mercury barometer has a glass column about 30 inches long, closed at one end, with a mercury-filled reservoir. High atmospheric pressure forces the mercury higher in the column because of the weight of the air outside. Low pressure allows the mercury to drop to a lower level inside the column.

30.65

Each notch is worth 1.0

1037.0

1038.0

1039.0

Each notch is worth 0.01

Page 13 of ESRT!

Air pressure is NOT the same everywhere on Earth

On Mount Everest:Pressure = 300mb

At Sea Level:Pressure = _____ mb = ________ in

(ESRT pg 13!)Tremendous Pressure

Give it a try!

29 in = _____ mb 988 mb = _____ in

1013.3 29.92

982.0 29.17 29.18

Why don’t we feel atmospheric pressure?

– Fluids inside our bodies exert same pressure as atmosphere– Example: Travel from high to low elevation, ears “pop” *

small pockets of air behind eardrums contract and expand to adjust to pressure*

Relationships• As altitude increases, pressure decreases

(inverse)

• As temperature increases, pressure decreases (inverse)

• As humidity increases, pressure decreases (inverse)

Altitude

Temperature

Humidity

Pressure

Pressure

Pressure

Why does pressure decrease with humidity?

• Water vapor is LIGHT compared to dry air

• Water Molecule– 2 Hydrogens (Atomic Weight = 1)– 1 Oxygen (Atomic Weight = 16)– Total Weight = 18

• Dry Air Molecules– 2 Nitrogens (Atomic Weight = 14) Total Weight = 28– 2 Oxygens (Atomic Weight = 16) Total Weight = 32

30.7128.7329.9229.5329.915

1033.01016.0995.5972.0992.2

•At what altitude do you most commonly experience one

atmosphere of pressure?

Sea Level