Air Pressure and Wind. What is air pressure? The force exerted by air molecules as they collide with...
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Transcript of Air Pressure and Wind. What is air pressure? The force exerted by air molecules as they collide with...
Air Pressure and Wind
What is air pressure?
• The force exerted by air molecules
as they collide with a surface• The weight of the atmosphere as it
pushes on Earth’s surface
What is air pressure?
kgkg
• Air has mass• Gravity pulls these
molecules towards Earth giving them weight
• The weight of the molecules is air pressure
What is air pressure?
• At sea level the weight of air pushing down is 14.7 pounds per square inch
• The weight on the roof of a typical house is about 2.1 million kg (4.6 million lbs)
Why don’t all of our houses collapse? Or Why aren’t we all squished?
What is air pressure?
• Air pressure is exerted (pushes) in all directions
• An equal force pushing down is balanced by air pushing up
Measuring air pressure
• The barometer is the instrument used to measure air pressure
• 2 types of barometers– Mercury– Aneroid
Mercury Barometer
Measuring air pressure
• As the weight of the air increases, the mercury rises
Measuring air pressure
• As the weight of the air decreases, the mercury lowers
Measuring air pressure
The Aneroid barometer• A capsule with most of
the air removed changes size as the pressure outside of it increases or decreases
• This moves the needle
Measuring air pressure
• Pressure will be measured in– Mm Hg– Inches of Hg– Milibars
• Average Pressure at sea level– 1013.25 mb = 29.92
in. Hg
Why does air pressure change?
• 3 factors that affect pressure:
– Elevation/Altitude– Temperature – Humidity
Changes inAIR PRESSURE
Humidity Temperature Elevation
Complete the graphic organizer by filling in the 3 factors that affect pressure. Then create branches explaining how they cause pressure to change.
Changes in air pressure
• Altitude
(height above sea level)
As the altitude increases pressure decreases
As the altitude decreases pressure increases
Changes in air pressureHumidity
(the amount of water vapor in air)
– Water molecules weigh less than O2 or N2
– Water vapor replaces these molecules in humid air
As humidity increases, pressure decreases
As humidity decreases, pressure increasesHUMID AIRDRY AIR
Changes in air pressure
Temperature– In warm air the molecules are far apart.– In cool air the molecules are closer together
As air temperature increases, pressure decreases
As air temperature decreases, pressure increases
Let’s Summarizedecrease Pressure increase Pressure
Temperature
Altitude
Humidity
Low Pressure
Generally associated with stormy weather.
The air is rising.
High Pressure
Generally associated with clear skies.
Air is sinking.
Factors Affecting Wind Direction and Speed
What makes the wind blow?
• Air moves from
HIGH PRESSURE to LOW PRESSURE
• This movement of air is WIND
Factors Affecting Wind Direction
• Coriolis Effect
• Pressure Gradients (differences in pressure HIGH vs LOW)
• Friction (resistance)
Pressure Gradients
• Pressure gradient:– A difference in
pressure from one place to another
• Remember wind blows from HIGH to LOW
– The stronger the gradient the faster the wind
– The faster the wind the more curve from the Coriolis Effect
Friction
• Friction between the air and the ground slows wind.
• The higher above the surface the faster the wind will blow
• The higher above the surface the more curve due to Coriolis
Review Questions
• How can we measure air pressure?
• What are the 3 factors that affect wind direction?
• What are the 3 factors that affect air pressure?
• How does a pressure gradient affect the speed of wind? Direction of wind?