Mike Reilly – Air Under Pressure Lesson
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Teacher: Mike Reilly
School: Islip High School
Class: World of Technology and or Principles in Engineering
Lesson: Air Under Pressure
Summary
Students are introduced to air masses, with an emphasis on the differences between and
characteristics of high- versus low-pressure air systems. Students also hear about weather
forecasting instrumentation and how engineers work to improve these instruments for
atmospheric measurements on Earth and in space.
Engineering Connection
Engineers are involved in many aspects of weather forecasting and weather appropriate design.
They develop weather instruments, including barometers to measure air pressure, which are
essential to our understanding of the Earth's weather systems. They design software to analyze
and integrate complex weather information for meteorologists to use. They even help develop
websites (and software) to present weather information in the most informative and pleasing way
for people to understand. Civil engineers utilize weather data when designing bridges, buildings
or other structures, to ensure that those designs are appropriate for the climate of their locations.
Environmental engineers utilize weather measurements to determine the placement and
effectiveness of renewal energy technologies, such as wind farms and solar arrays.
Grade Level: 9-12
Time Required: approx. 2-3 class periods
Group Size: None
Learning Objectives
After this lesson, students should be able to:

Describe the effect of the sun on air masses in the Earth's atmosphere.


Compare and contrast high- and low-pressure air systems.
Explain that engineers design instrumentation, such as a barometer, to help
analyze the Earth’s weather systems.
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Introduction/Motivation
Have you ever blown up a balloon and let go of it without sealing it with a knot? What happens?
That's right: it zips around in the air until the air is gone, and it is finally deflated. That occurs
because there is a pressure difference between the air inside the balloon and the surrounding air.
Even though we cannot always see or feel the air, it actually has a mass. It also has other
physical properties, such as density and pressure. What does that mean for our atmosphere?
Large bodies of air exist in our atmosphere where all the air within that region has a similar
temperature, pressure and humidity. We call those bodies of air with similar characteristics air
masses. Air masses change and shift all the time, but on any given day, there are many different
air masses in our atmosphere, all with their own unique air pressure. Thinking back to the balloon
example, we know that air pressure differences can cause air to move — similar to the balloon
zipping around the room. The movement of those air masses in our atmosphere contributes to
the weather we experience every day.
We know that the sun plays a significant role in the weather we experience on Earth. But how
does the sun relate to air masses? The sun heats up our atmosphere and the Earth's surface, but
the heating takes place unevenly because the sun's rays hit different areas of the Earth at
different angles. Variations on the Earth's surface provide even more room for uneven heating.
The air above water, for example, is typically cooler than the air above land, and the air above
lighter colored surfaces is typically cooler than the air above darker ones (very simply, because
dark color absorb more heat). Because the sun heats pockets of air to different temperatures, the
sun actually helps create the different air masses in our atmosphere.
High and low-pressure areas are affected by the interaction of air and temperature (among other
things) in our atmosphere. Areas of high air pressure are often characterized by light winds and
clear skies. With no clouds to reflect the sunlight, high-pressure regions also usually experience
higher daytime temperatures. Low-pressure areas then, are regions where the atmospheric
pressure is lower than that of the surrounding area. Low-pressure areas are associated with
winds and cloudy, overcast skies. Due to the clouds, the sun's rays have a harder time
penetrating low-pressure regions, usually leading to lower temperatures. Falling air pressure
usually indicates that a storm of some sort is approaching. On the other hand, rising air pressure
is usually an indication that the weather is clearing up.
Have you ever heard of a barometer? Barometers are the instruments that meteorologists use to
gauge changes in air pressure in order to make their forecasts. Engineers design the
instrumentation that meteorologists use to help predict the changes in weather, including
barometers. Engineers are always trying to improve the different instruments used to make
weather measurements and predictions on Earth and in space. Weather satellites, orbiting our
Earth, are designed by engineers to take pictures and measurements of moving air masses to
help us understand how the weather is changing on our planet. Engineers develop and use new
technologies to make weather instrumentation more accurate and helpful.
Changes in weather happen due to many reasons, including moving air masses and air pressure,
as well as humidity and temperature. All of these things work together as parts of the system of
weather that affects us every day.
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Lesson Background & Concepts for Teachers
Why do air masses move around? The Earth's air masses move because the changes in air
temperature also mean changes in air pressure and density. As the temperature of air increases,
the air expands. The same amount of air occupies more space when it heats up than when it is
cold. Density of air is equal to the mass of the air divided by its volume. So in other words, when
air is heated, its volume increases, but its density decreases. Things with lower density float on
top of things with higher density. For example, ice cubes float in water because water is denser
than the ice cubes. The same phenomenon happens in our atmosphere: warm air rises because
it "floats" on top of colder air. In other words, the rule of thumb is that hot air rises and cold air
sinks. This simple principle actually guides much of the weather patterns we experience on Earth.
There are four major types of air masses that influence the weather in the United States: (1)
continental tropical, (2) maritime tropical, (3) continental polar and (4) maritime polar. To simply
things, maritime refers to air masses that form over oceans, while continental means air masses
that formed over land. The air masses that form over oceans (maritime) are more humid than
continental air masses that form over dry land. Air masses that form in the tropics have low air
pressure, and air masses that form closer to the poles are higher air pressure.
Vocabulary/Definitions
Air Mass:
Air Pressure:
Anticyclones:
Barometer:
Continental:
Cyclones:
High-Pressure
Area:
Low Air Pressure:
Maritime:
A large region of air that has similar temperature, pressure, and humidity.
The force caused by the weight of air pushing down on an area.
A name sometimes used to refer to high-pressure areas.
A tool used to measure air pressure.
Refers to air masses that form over land.
A name sometimes used to refer to low-pressure areas.
Region of air where the air pressure is greater than that of the surrounding
area.
Region of air where the air pressure is lower than that of the surrounding
area.
Refers to air masses that form over oceans.
Lesson Closure
Today we want to remember that hot air rises and cold air sinks. The sun heats up our
atmosphere and the Earth's surface, but the heating takes place unevenly because the sun's rays
hit the Earth's surface at different angles. The many different angles can be influenced by the
topography and variations on the Earth's surface itself. The moving air that circulates in our
atmosphere is called an air mass and can involve high or low air pressure.
Also, areas of high air pressure are often characterized by light winds and clear skies. Lowpressure areas are associated with winds and cloudy, rainy skies. Usually, falling air pressure
usually indicates that a storm of some sort is approaching; rising air pressure is usually an
indication that the weather is going to be fair.
Engineers design the instruments — including barometers — to measure air pressure, which
meteorologists use to help analyze the Earth's weather systems. Engineers are always trying to
improve these instruments to make them more accurate, more efficient, or to utilize new
technologies.
Mike Reilly – Air Under Pressure Lesson
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Assessment
Pre-Lesson Assessment
Discussion Question: Ask a discussion question to get students to think about the upcoming
lesson. After soliciting answers, explain that these questions will be answered during the lesson.

Why does the weather change from day to day?

How do engineers help us make weather predictions?
Post-Introduction Assessment
Voting: Ask a true/false question and have students vote by holding thumbs up for true and
thumbs down for false. Count the votes and write the totals on the board. Give the right answer.

True or False: Cold air rises and hot air sinks. (Answer: False; hot air rises and cold air
sinks.)

True or False: Wind and storms are caused by the movement of air masses. (Answer:
True)

True or False: The sun helps create the different air masses in our atmosphere by
heating up the air to different temperatures. (Answer: True)

True or False: Areas of low air pressure are often characterized by light winds and clear
skies. (Answer: False; areas of high air pressure tell us that clear skies are ahead.)

True or False: Engineers design the weather instruments that are used in forecasting the
weather on TV or radio. (Answer: True; engineers design instruments to help all
meteorologists make weather forecasts.)

True or False: It is not possible to measure the Earth's weather from space. (Answer:
False; in additional to designing instruments to help make weather forecasts, engineers also
design instruments to help us predict the weather from space as well as on Earth.)
Lesson Summary Assessment
Explain It: Often, engineers have to explain complex concepts to an audience with little prior
knowledge of the topic. Have students write a short paragraph or story to explain air pressure to a
younger student. From what they learned today, have them include information on how engineers
help us understand air pressure and weather.
Think about Constraints: Engineers need to consider the economic, social and environmental
impacts of their designs on their audience. For weather forecasting, the audience includes all of
us who listen to weather reports and forecasts. As a class, generate a list of how weather
forecasts (and how accurate the forecast is) affect us socially, economically, and environmentally.
For example, we may decide what to wear and when to go outside by listening to a weather
forecast (social); a weather forecast could help us decide what clothing to buy or what type of
building material we use for a house (economic); a weather forecast could also help us learn
about the amount of rain or snow in an area available for drinking water (environmental).
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References
National Weather Service, Southern Region Headquarters, Little Rock, AR. Copyright © NOAA
http://www.srh.noaa.gov/lzk/images/sfc122500a.jpg
U.S. Centennial of Flight Commission,
http://www.centennialofflight.gov/2003FF/pressure/weatherman_pointing_lg_green.gif
Standards:
Science: 2.1b The transfer of heat energy within the atmosphere, the hydrosphere, and Earth's
interior results in the formation of regions of different densities. These density differences result in
motion. (Grades 9 - 12)
Technology: Standard 5: Students will apply technological knowledge and skills to design,
construct, use, and evaluate products and systems to satisfy human and environmental needs.