Download Air Pressure and Wind

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?
1. The same thing as
gravity
2. The weight of the
atmosphere
pushing downward
3. A form of pollutant
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Why Don’t We Get Crushed By The
Pressure Of The Atmosphere?
1. The air is not that
heavy
2. Air pressure is
exerted in all
directions, and we
are in equilibrium
3. The water in our
bodies prevents it
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Why Did The Oil Drum Collapse?
1. The water weakened it
2. The atmosphere
suddenly got heavier
3. The cooling vapor took
up less space than
before and created a
drop in pressure
inside. The regular air
pressure then crushed
the drum.
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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 (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
Humidity
Temperature
Elevation
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
HUMID AIR
DRY AIR
As humidity decreases, pressure increases
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
Decrease
Temperature
Altitude
Humidity
Pressure
Increase
Pressure
Low Pressure
Generally associated with
stormy weather.
The air is rising.
High Pressure
Generally associated with
clear skies.
Air is sinking.
What makes the wind blow?
• Air moves from
HIGH PRESSURE to
LOW PRESSURE
• This movement of air
is WIND
What does a barometer measure?
1. Atmospheric
pressure
2. The humidity of
the air
3. Air quality
4. How much it has
rained
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What affects air pressure?
1.
2.
3.
4.
Altitude
Humidity
Temperature
All of the above
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Why is water vapor less dense than
air?
1. There is less of it
2. H2O has less mass
than O2 or N2
3. It is hotter, so it has
less mass
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Low pressure is usually associated
with…
1.
2.
3.
4.
Sunny skies
Deserts
Earthquakes
Stormy weather
and rising air
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High pressure is usually associated
with…
1. Rain
2. Tornadoes
3. Sunny, dry
weather with
sinking air
4. Pushy car
salesmen
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Factors Affecting Wind
Direction and Speed
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!
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
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?
1. Altitude, Humidity,
and Temperature
2. Altitude, Humidity,
and Coriolis Effect
3. Coriolis, Pressure,
Gradients, and
Friction
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What are the 3 factors that affect
air pressure?
1. Altitude, Humidity,
and Temperature
2. Coriolis, Pressure,
Gradients, and
Frction
3. Sunlight,
Convection, and
Friction
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How does a pressure gradient
affect the speed of wind?
1. The stronger the
gradient, the
weaker the wind
2. The stronger the
gradient, the
stronger the wind
3. It does not effect
the speed
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Why does the Coriolis Effect cause
wind to deflect?
1. The wind was
already curving;
the Coriolis Effect
only effects
airplanes
2. The spinning of
the Earth causes
the path to curve
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How does friction affect wind
speed?
1. Objects or rough
surfaces cause a
drag on the wind
2. Friction makes the
wind faster
3. Friction creates
wind
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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?
1. North and South
Pole Only
2. 0 and 60 Degrees
Latitude
3. 30 and 90
Degrees Latitude
4. Over the Ocean
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Where will you find areas of low
pressure on Earth?
1. North and South
Pole Only
2. 0 and 60 Degrees
Latitude
3. 30 and 90
Degrees Latitude
4. Over the Ocean
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What Creates Santa Ana Winds?
1. High Pressure Over
Land and Low
Pressure Over
Ocean
2. Low Pressure Over
Land and High
Pressure Over
Ocean
3. Politicians In Santa
Ana
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