### Ch. 19 Wind and Air Pressure

```Pearson Science Book
SC.912.N.1.1, SC.912.N.2.5
SC.912.E.7.3
 Describe how air pressure is exerted on objects.
 Explain how changes in air pressure affect the mercury
column of the barometer.
 Identify the ultimate energy source for wind.
 Describe how the Coriolis effect influences freely
moving objects.
Using vocabulary sheet write the terms and what you think they
mean. Later after the lesson you will write the scientific
definition.
 Air pressure
 Barometer
 Coriolis effect
 Jet stream
Describe how air pressure is exerted on objects.
2. What happens to the mercury column of a barometer
when air pressure changes?
3. What is the ultimate energy source for wind?
4. How does the Coriolis effect influence free-moving
objects?
1.
Topic
Main Ideas
Air Pressure Defined
Air pressure is…
Measuring Air Pressure
Factors Affecting Wind
 Purpose – Students prove air has mass by comparing
the mass of a balloon when empty and when filled.
 Materials – balloon, balance
 Procedure – Blow up a balloon and determine its mass
using a balance. Remove the balloon, release the air,
and replace the balloon on the balance. Find the mass
again.
 Expected Outcomes – Students will see that they empty
balloon is lighter than the air filled balloon.
 Materials
 Clear cup, cork, beaker, tray
 Procedure
 Try to push a cork to the bottom of the water using only
an upside-down cup. Draw a sketch of the result on
page 2. How does this prove that air takes up space?
 Scientist define matter as anything that has mass, and
takes up space
 Air pressure is simply the pressure exerted by the
weight of air above.
 Average air pressure at sea level is about 1 kg per
square centimeter. Roughly the same pressure as a
column of water 10 meters in height.
 Air pressure is exerted in all directions – down, up, and
sideways. The air pressure pushing down on an object
balances the air pressure pushing up on the object.
Average air pressure at sea level is about 1 kilogram per square
centimeter.
 Meteorologists measure atmospheric pressure with a
unit of millibars.
 Standard sea level pressure is 1013.2 millibars.
 A barometer is used for measuring air pressure.
 Bar = pressure
 Metron = measuring instrument.
 Described the
atmosphere as a vast
ocean of air that exerts
pressure on us and all
objects around us.
 To measure the force, he
filled a glass tube, closed
at one end, with mercury.
Then he put the tube
upside down into a dish
of mercury.
 When air pressure increases, the mercury in the tube
rises. When air pressure decreases, so does the height
of the mercury column.
 Improvements from Torricelli’s barometer have been
made but, the barometer is still used for measuring air
pressure.
 Aneroid barometer is
smaller and more portable
 It uses a metal chamber
with some air removed.
aneroid barometer is that it
can be easily connected to
a recording device.
 Provides continuous record
of pressure changes with
the passage of time.
 Purpose – students show that air pressure is exerted in
all directions - down, up, and sideways.
 Materials – glass, water, cardboard, sink
 Procedure – Fill the glass with water to the brim. Place
a piece of cardboard on top of the glass. Working over
a sink, hold the cardboard in place and invert the glass.
Then, remove your hand from the cardboard.
 Expected Outcomes – The pressure of the air pushing
up on the cardboard holds it against the full glass of
water, preventing it from spilling.
 Wind is the result of horizontal differences in air
pressure. Air flows from areas of higher pressure to
areas of low pressure.
 The unequal heating of Earth’s surface generates
pressure differences.
 Solar radiation is the ultimate energy source for most
wind.
 If Earth did not rotate, and if there were no friction
between moving air on Earth’s surface, air would not
flow in a straight line from areas of higher pressure to
areas of lower pressure.
 Three factors combine to control wind:
1. Pressure differences
2. The Coriolis Effect
3. Friction
 Wind is created by differences in pressure – the greater
the pressure the greater the differences are, the
greater the wind speed.
 Air pressure is determined by using barometers. The
data are shown on maps using isobars.
 Isobars are lines on a map that connect places of equal
air pressure.
 The spacing of isobars indicates the amount of
pressure change occurring over a given distance.
 These pressure changes are expressed as the pressure
 Closely spaced isobars indicate a steep pressure
gradient and high winds. Widely spaced isobars
indicate a weak pressure gradient and light winds.
 The pressure gradient is the driving force of wind. It
has both magnitude and direction.
 Its magnitude is reflected in the spacing of isobars.
 The direction of force is always from areas of high
pressure to areas of low pressure and at right angles to
the isobars.
For this particular map, isobar lines are most closely spaced in
the low-pressure cell, which indicates fastest wind speeds in this
cell.
Topic
Main Ideas
Air Pressure Defined
Air pressure is the weight of air above. It
is exerted in all directions.
Measuring Air Pressure
Air pressure is measured with
barometers, using the principles that
fluids will deform if the weight of the air
is exerted on them.
Factors Affecting Wind
and friction
By William Kamkwamba and Bryan Mealer
 On page 8 you will need to answer the following
questions in complete sentences.
 Will be posted during the reading.
1.
2.
3.
4.
5.
What did William wonder as a truck rumbled past the
fields where he worked?
What did William’s father tell his family after the rain
When did William decide to build electric wind?
What happened right before William shouted, “I made
electric wind?”
Why did William want to build another windmill?
 Compare and Contrast- Take a few minutes and think
about the character in the story. Compare and contrast
your lives. You need at least 5 in each category. We
have already discussed ages and times.
 Imagine you were given money to go to the mall with the
main character of the book. List 10 items you would
purchase and why. Then list 10 items he would
purchase and why.
 The Coriolis effect describes how Earth’s rotation
affects moving objects.
 All free-moving objects or fluids, including wind, are
deflected to the right of their path of motion in the
Northern Hemisphere.
 In the Southern Hemisphere, they are deflected to the
left.
Coriolis Effect
Because the Earth
rotates 15’ each
hour, the rocket’s
path is curved and
veers to the right
from the North Pole
to the equator.
360 degrees
 The apparent shift in wind direction is attributed to the
Coriolis effect.
 This deflection:
1. Is always directed at right angles to the direction of
airflow.
2. Affects only wind direction and not wind speed
3. Is affected by wind speed – the stronger the wind, the
greater the deflections
4. Is strongest at the poles and weakens toward the
equator, becoming nonexistent at the equator.
 Friction acts to slow air movement, which changes wind
direction.
 When air is above the friction layer, the pressure
gradient causes air to move across the isobars.
 As soon as air starts to move, the Coriolis effect acts at
right angles to this motion . The faster the wind speed,
the greater the deflection.
 The most prominent features of airflow high above the
friction layer are the jet streams.
 Jet streams are fast moving rivers of air near the
troposphere that travel between 120-240 kilometers
per hour in a west-to-east direction.
 Air close to Earth’s surface, the roughness of the terrain
determines the angle of the airflow across the isobars.
 Over the smooth ocean surface, friction is low, and the
angle of the airflow is small.
 Over rugged terrain, friction is higher, winds move more
slowly and cross the isobars at greater angles.
 Figure A – Upper level
wind flow is balanced by
the Coriolis effect and
 Figure B – Friction causes
surface force winds to
cross isobars and move
toward lower pressure
areas.
 Friction affects wind speed and direction.
 Coriolis effect affects wind direction only.
Topic
Main Ideas
Air Pressure Defined
Air pressure is the weight of air above. It
is exerted in all directions.
Measuring Air Pressure
Air pressure is measured with
barometers, using the principle that
fluids will deform if the weight of air is
exerted on them.
Factors Affecting Wind
friction
the class.
 Air pressure is exerted in all directions – down, up, and
sideways. The air pressure pushing down on an object
balances the air pressure pushing up on the object.
 When air pressure increases, the mercury in the tube
rises. When air pressure decreases, so does the height
of the mercury column.
 Solar radiation (the sun) is the ultimate source for wind.
 The Coriolis effect deflects all free-moving objects to
the right of their path of motion in the Northern
Hemisphere. In the Southern Hemisphere, they are
deflected to the left.
SC.912.N.2.5, SC.912.N.3.5
SC.912.E.7.3, SC.912.E.7.5
 Explain how winds blow around pressure centers in the
Northern and Southern Hemispheres.
 Describe the air pressure patterns within cyclones and
anticyclones.
 Describe how friction controls the net flow of air around
a cyclone and an anticyclone.
 Cyclone
 Anticyclone
 westerlies
Describe how winds blow around pressure centers in
the Northern and Southern Hemisphere.
2. Compare the air pressure for a cyclones and an
anticyclones?
3. How does friction control net flow of air around a
cyclone and an anticyclone?
4. How does the atmosphere attempt to balance the
unequal heating of Earth’s surface?
1.
Concept
Cyclones rotate counter clockwise.
Net flow of air is inward around a
cyclone.
Anticyclones rotate counterclockwise.
Coriolis effect deflects winds to the right.
Hemisphere
 Lows, or cyclones (kyklon = moving in a circle) – are
centers of low pressure.
 Highs, or anticyclones, are centers of high pressure.
 In cyclones, the pressure decreases from the outer
isobars toward the center. In anticyclones, just the
opposite occurs, the values of the isobars increase
from the outside toward the center.
The two most significant factors that affect wind are the
pressure gradient and the Coriolis effect.
 Winds move from higher pressure to lower pressure and
are deflected to the right or left by Earth’s rotation.
 When the pressure gradient and the Coriolis effect are
applied to pressure centers in the Northern
Hemisphere, winds blow counterclockwise around a
low. Around a high, they blow clockwise.
 In the Southern Hemisphere just the opposite happens.
 In either hemisphere, friction causes a net flow of air
inward around a cyclone and a net flow of air outward
around an anticyclone.
 Rising air is associated with cloud formation and
precipitation, whereas sinking air produces clear skies.
 A low-pressure center causes a net accumulation of air
which increases pressure.
Face to Face – Explain words on board without saying the word.
 Clouds
 Rain
 Atmosphere
 Water vapor
 Oxygen
 Cirrus
 Stratus
 Low Pressure
 Sleet
 Nimbus clouds
 Nitrogen
 Cumulus clouds
 Snow
 High Pressure
 Friction
 Barometer
 Hydrogen
 http://usatoday30.usatoday.com/weather/tg/whighlow
/whighlow.htm
 Read article as a class.
 Come up with questions using “Hot Science ?’s”
 Atmospheric pressure at the Earth's surface is one of the
keys to weather, which is one reason weather maps feature
H's and L's, representing areas of high and low air pressure.
High and low pressure areas are important because they
affect the weather.
 The weather maps, such as those on television, show what's
happening at the Earth's surface, and that's what we're
 As the name says, a "high" is an area where the air's
pressure is higher than the pressure of the surrounding air.
A "low' is where it's lower. Meteorologists don't have any
particular number that divides high from low pressure; it's
the relative differences that count.
 The pressure is high at the surface where air is slowly descending —




much too slowly to feel. And, this is going on over a large area, maybe a
few hundred square miles. As air descends, it warms, which inhibits the
formation of clouds. This is why high pressure is generally — but not
quite always — associated with good weather.
The air that descends in high-pressure areas has to get to high altitudes
in some way, and its done by rising in areas where the pressure at the
surface is low.
As air rises it cools. As the air cools, the humidity in it begins to
condense into tiny drops of water, or if it's cold enough, into tiny ice
crystals. If there's enough water or ice, rain or snow begin to fall. This is
why low pressure is associated with bad weather.
As shown in the graphic above, the air descending in high pressure flows
out in a clockwise spiral in the Northern Hemisphere. Air flowing into an
area of low pressure rises, making a counterclockwise spiral on the way
in.
For more on why the wind flows in the directions it does, go to the
USATODAY.com Guide to the science of the atmosphere and look at the
links from the section on "The what and why of the wind."
Rising air is associated with cloud formation and precipitation.
 Picture shows the
relationship between
surface convergence
(inflow) and divergence
(outflow) needed to
maintain a low-pressure
center.
 Surface convergence
around a cyclone causes
a net upward movement.
 Low-pressure centers can produce bad weather in any
season.
 Lows move roughly in a west-to-east direction across
the United States.
 They require a few days up to more than a week to
make the journey.
 Their paths can be somewhat unpredictable.
 Underlying cause of wind is the unequal heating of
Earth’s surface.
 The atmosphere balances these differences by acting
as a giant heat-transfer system. This system moves
warm air toward high latitudes and cool air toward the
equator.
The atmosphere transfers heat by moving warm air toward high
latitudes and cool air toward the equator.
You will have 15 minutes to answer the essential questions in
complete sentences. Remember be prepared to share your
Concept
Hemisphere
Cyclones rotate counter clockwise.
Northern
Net flow of air is inward around a
cyclone.
Both
Anticyclones rotate counterclockwise.
Southern
Coriolis effect deflects winds to the right. Northern
 In the Northern Hemisphere, winds blow
counterclockwise and inward around a low, and
clockwise and outer around a high. It is exactly
opposite in the Southern Hemisphere.
 In cyclones, air pressure decreases toward the center of
the cell. In anticyclones, the air pressure increases
toward the center of the cell.
 The effect of friction is to cause a net flow of air inward
around a cyclone and a net flow outward about an
anticyclone.
 The atmosphere acts like a huge heat-transferring
system, transporting warm air from the equator toward
the poles and cold air from the poles toward the
equator.
SC.912.N.4.1
SC.912.E.7.2, SC.912.E.7.3
Identify the causes of local winds
2. Describe the general movement of weather in the
United States.
3. Compare and Contrast weather patterns and
characteristics of El Nino and La Nina events.
1.
 Prevailing winds
 Anemometer
 El Nino
What are local winds, and how are they caused?
2. Describe the general movement of weather in the
United States.
3. What happens when strong, warm countercurrents
flow along the coasts of Ecuador and Peru?
4. How is a La Nina event recognized?
1.
Precipitation
Extremely low
Extremely high
Location
Dominant Wind System
 Small scaled winds produced by locally generated
pressure gradient are known as local winds.
 The local winds are caused either by topographic
effects or by variations in surface composition – land
and water - in the immediate area.
 Coastal areas in warm summer months, land surface is
heated more intensely during the daylight hours than
an adjacent body of water is heated.
 The air above the land surface heats, expands, and
rises, creating an area of lower pressure.
 A sea breeze then develops because cooler air over the
water at higher pressure moves towards the warmer
land and low pressure air.
 At night , the reverse occurs.
 Land cools more rapidly than the sea. A land breeze
develops.
 Two basic wind measurements:
 Direction
 Speed
 Winds are always labeled by the direction from which
they blow.
 The instrument most commonly used to determine wind
direction is the wind vane.
 Commonly located on
buildings and always
point into the wind.
 Wind direction is often
shown on a dial
connected to it.
 Dial indicates wind
direction by N, S, E, or W
 On a scale of 0’-360 ‘
 Degree Scale for a




weather vane.
North = 0’ or 360’
East = 90’
South = 180’
West = 270’
 How does the position of
a wind vane tell you
which direction the wind
is blowing?
 The wind vanes point into
the wind.
 When wind consistently blows more often from one
direction than from any other, it is called a prevailing
wind.
 In the United States, the westerlies consistently move
weather from west to east across the continent.
 Winds associated with the westerlies, as measured at
the surface, often vary considerably from day to day
and from place to place.
 The direction of airflow associated with the trade winds
is much more consistent.
 Anemometer - anemo = wind, metron = measuring
instrument
 A cup anemometer is commonly used to measure wind
speed.
 The wind speed is read from a dial much like the
speedometer of an automobile.
 You will be given 8 words from the chapter
 Cut them into squares
 Use the squares to make a word chain. Put the chain
together so it shows a relationship among the words.
 There is more than one way to make a chain.
 Once you have completed the chain glue it to the top of
 On the bottom half of the paper, use the chain to write a
paragraph that uses all the words.
 cyclone
 anticyclone
 clockwise
 counter clockwise
 high pressure
 low pressure
 Northern Hemisphere
 Southern Hemisphere
 The cold Peruvian current flows toward the equator
along the coasts of Ecuador and Peru. This flow
encourages upwelling of cold nutrient-filled waters that
contain the food source for millions of fish, particularly
anchovies.
 Near the end of the year, a warm current that flows
southward along the coasts of Ecuador and Peru
replaces the cold Peruvian current.
 At regular intervals of three to seven years, these warm
countercurrents become unusually strong and replace
normally cold offshore waters with equatorial waters.
 They call these episodes of ocean warming that affect
the eastern tropical Pacific El Nino.
 Usually strong countercurrents accumulate large
quantities of warm water that block the upwelling of
colder, nutrient-filled waters.
 Some inland areas that are normally arid receive an
abnormal amount of rain.
An episode occurring every three to seven years – of ocean
warming that affects the eastern tropical Pacific. Warm
countercurrents become unusually strong and replace normally
cold offshore waters with equatorial waters.
 When surface temperatures in the eastern Pacific are
colder than average, a La Nina event is triggered that
has a distinctive set of weather patterns.
 Winter blows colder than normal air over the Pacific
Northwest and northern Great Plains. The Northwest
also experiences more precipitation.
 It warms much of the rest of the United States.
 Can increase hurricane activity.
 Both have a great affect on world climate and vary
greatly.
 These phenomena remind us that the air and ocean
conditions of the tropical Pacific influence the state of
the weather almost everywhere.
You will have 15 minutes to answer the essential questions in
complete sentences. Remember be prepared to share your
 Local winds are small scaled winds caused by local
variations in air pressure, which are caused by
topography and unequal heating of land and water, or
unequal heating of air above slopes and valleys.
 Weather generally moves from west to east in the
United States.
 An El Nino event blocks normal upwelling of cold,
nutrient-laden waters off the shores of these countries,
and causes heavy precipitation island. El Nino can
have far-reaching effects on weather patterns of regions
that are great distances from Ecuador and Peru.
 La Nina is triggered when surface temperatures in the
eastern Pacific are colder than average.
Precipitation
Location
Dominant Wind System
Extremely low
Arabian Desert