# Air Pressure and Wind.

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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? Air has mass
Gravity pulls these molecules towards Earth giving them weight The weight of the molecules is air pressure kg

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? CHECK THIS OUT!!! Extreme Atmospheric Pressure

What is air pressure? Air pressure is exerted (pushes) in all directions An equal force pushing down is balanced by air pushing up

What Is Air Pressure? The same thing as gravity
The weight of the atmosphere pushing downward A form of pollutant

Why Don’t We Get Crushed By The Pressure Of The Atmosphere?
The air is not that heavy Air pressure is exerted in all directions, and we are in equilibrium The water in our bodies prevents it

Why Did The Oil Drum Collapse?
The water weakened it The atmosphere suddenly got heavier The cooling vapor took up less space than before and created a drop in pressure inside. The regular air pressure then crushed the drum.

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 mb = in. Hg

Why does air pressure change?
3 factors that affect pressure: Elevation/Altitude (p414) Temperature (p416) Humidity (p416)

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 pressure
Altitude Drawing High Altitude / Low Pressure Low Altitude / High Pressure

Changes in air pressure
Humidity (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 increases HUMID AIR DRY AIR

Changes in Air Pressure
Humidity Drawing Low Humidity / High Pressure High Humidity / Low Pressure

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

Changes in air pressure
Temperature Drawing High Temperature / Low Pressure Low Temperature / High Pressure

Let’s Summarize Temperature Altitude Decrease Pressure Increase
Humidity

Low Pressure Generally associated with stormy weather.
The air is rising.

High Pressure Generally associated with clear skies. Air is sinking.

What does a barometer measure?
Atmospheric pressure The humidity of the air Air quality How much it has rained

What affects air pressure?
Altitude Humidity Temperature All of the above

Why is water vapor less dense than air?
There is less of it H2O has less mass than O2 or N2 It is hotter, so it has less mass

Low pressure is usually associated with…
Sunny skies Deserts Earthquakes Stormy weather and rising air

High pressure is usually associated with…
Rain Tornadoes Sunny, dry weather with sinking air Pushy car salesmen

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

What makes the wind blow?
Island Example

Factors Affecting Wind Direction
Coriolis Effect Coriolis-2.mp4 Pressure Gradients (differences in pressure HIGH vs LOW) Friction (resistance)

The Coriolis Effect An object moving over Earth’s surface will curve away from its intended path This is due to Earth’s rotation Faster at the equator Slower at the poles

The Coriolis Effect Coriolis-1.mp4 Guidelines (p419):
objects are deflected to the RIGHT in the Northern Hemisphere and the LEFT in the Southern Hemisphere The effect (curve) increases as the speed increases The effect DOES NOT depend on the objects direction The effect is greater at the poles and less at the equator Most noticeable of large distances (Not in TOILETS)

The Coriolis Effect Let’s Draw!

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

Friction Little friction in the upper troposphere allows a jet stream to from moving air west to east. The jet stream supplies energy to storms and directs the path of weather across the United States Affects airplanes as they travel coast to coast

Jet Stream

Review Questions 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? Why does the Coriolis Effect cause wind to deflect? Can you witness the Coriois Effect in your bathroom? How does friction affect wind speed?

What are the 3 factors that affect wind direction?
Altitude, Humidity, and Temperature Altitude, Humidity, and Coriolis Effect Coriolis, Pressure, Gradients, and Friction

What are the 3 factors that affect air pressure?
Altitude, Humidity, and Temperature Coriolis, Pressure, Gradients, and Frction Sunlight, Convection, and Friction

How does a pressure gradient affect the speed of wind?
The stronger the gradient, the weaker the wind The stronger the gradient, the stronger the wind It does not effect the speed

Why does the Coriolis Effect cause wind to deflect?
The wind was already curving; the Coriolis Effect only effects airplanes The spinning of the Earth causes the path to curve

How does friction affect wind speed?
Objects or rough surfaces cause a drag on the wind Friction makes the wind faster Friction creates wind

Global and Local Winds

Global Winds Global winds show the general direction the air is flowing throughout the globe. Refer to your worksheet for these winds The winds are named according to where the wind comes from or originates Ex. What would the name of this wind be?

Global Winds Climate Zones due to global winds:
Areas of low pressure are characterized by rising air, precipitation = Rainforest (0, 60) Areas of high pressure are characterized by sinking air, dry air = Deserts (30, 90) ** Add these areas to your worksheet

Continental and Local Winds
These winds can go opposite the expected global winds due to changes in local conditions: Continental Winds Monsoon Local Winds Sea breeze Land breeze Santa Ana Winds

Monsoon A Monsoon is a seasonal change in winds. Ex. India, North America

Sea Breeze: Rising Air, Sinking Air, High Pressure, Low Pressure, Dense Air, Less Dense Air, Cloud Formation

Land Breeze: Rising Air, Sinking Air, High Pressure, Low Pressure, Dense Air, Less Dense Air,

Santa Ana Winds Occur in Southern California in the late fall/early winter A high pressure forms as the desert regions As the air sinks it is compressed and usually warms.

Santa Ana Winds This creates an offshore wind (blows towards the ocean) The air is very dry and often wildfires are a result of this wind

Where will you find areas of high pressure on Earth?
North and South Pole Only 0 and 60 Degrees Latitude 30 and 90 Degrees Latitude Over the Ocean

Where will you find areas of low pressure on Earth?
North and South Pole Only 0 and 60 Degrees Latitude 30 and 90 Degrees Latitude Over the Ocean

What Creates Santa Ana Winds?
High Pressure Over Land and Low Pressure Over Ocean Low Pressure Over Land and High Pressure Over Ocean Politicians In Santa Ana

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