Weather
Lesson #7: Air Pressure and Air Fronts
Time Frame: 60 minutes
Learning Standards:
Science
Earth and Space Science: Weather
1) Explain how air temperature, moisture, wind speed and direction, and
precipitation make up the weather in a particular place and time.
Skills of Inquiry
 Ask questions and make predictions that can be tested.
 Recognize simple patterns in data and use data to create a reasonable explanation
for the results of an investigation or experiment.
 Record data and communicate findings to others using graphs, charts, maps,
models, and oral and written reports.
Technology/Engineering
Materials and Tools
1.1 Identify materials used to accomplish a design task based on a specific property,
i.e., weight, strength, hardness, and flexibility.
1.2 Identify and explain the appropriate materials and tools (e.g., hammer, screwdriver,
pliers, tape measure, screws, nails, and other mechanical fasteners) to construct a
given prototype safely.
Engineering Design
2.2 Identify relevant design features (e.g., size, shape, weight) for building a prototype of
a solution to a given problem.
Student will be able to:
1) Explain how air pressure influences weather and how barometer readings can be
used to make weather forecasts (predictions).
2) Explain how a barometer measures air pressure.
Resources and Materials:
Item
Science notebooks
Large glass jar
Balloons
Lighter
Newspaper
Large balloons
Straws
Index cards (3” x 5”)
Rubber bands
Amount
1 (in bin)
1 bag (in bin)
1 (in bin)
1 section (in bin)
1 bag (in bin)
1 box (in bin)
1 (in bin)
1 bag (in bin)
Scissors (not provided)
Metal can
Duct tape
Glass beaker
Plastic cup
Food coloring
Oil
Water (not provided)
Warm and cold air front handouts
(in classroom)
3 (in bin)
1 (in bin)
1 (in bin)
1 (in bin)
1 box (in bin)
1 (in bin)
(in classroom)
30 (in bin)
Focus Activity: Ask the students to write down what they know about air pressure in
their science notebooks. Get ideas from the students about air pressure and review
concepts as necessary. Air pressure is the weight of molecules pressing down on the
earth due to gravity, the heavier the weight of the air, the more air pressure on the
earth’s surface. Warmer air is lighter (less air pressure) and rises and colder air is
heavier (more air pressure) and sinks. The rise and fall and warm and cold air is what
creates winds.
Introduction: Review with students that weather occurs because of the interaction
between the sun, atmosphere, and the earth. Remind students that the atmosphere is
the layer of gases surrounding the earth. Air pressure is influenced by changes in
temperature (due to the sun). Explain that they will learn how to measure air pressure
and how to use air pressure measurements to make weather predictions.
Activity:
1) Explain that when there is low pressure, warm, moist air rises off of the earth. It
expands as it rises because warm air molecules are less dense. As this warm air
rises, it cools. When air cools it becomes denser and sinks back to the earth.
This is called high pressure. Write the following summary in a table on the board
and discuss it with the class (review density from the matter unit if necessary).
Have students copy the table into their science notebooks.
Low Pressure: warm air molecules, less dense, air rises
High Pressure: cold air molecules, more dense, air sinks
2) Do the following demonstration to show that warm air rises and cold air sinks.
Get out the glass jar with the wide mouth (labeled for the balloon demonstration).
Fill up a balloon with water so that it is big enough to sit on top of the opening of
the jar without slipping inside (but not too much bigger). If this demonstration
does not work, try again with a smaller balloon. Place some newspaper in the
bottom of the jar. Light the newspaper on fire and quickly place the balloon on
top of the jar. The balloon will bounce around. Why does this happen? Air
warmed from the fire is rising and trying to get out of the jar. When the fire goes
out the balloon will get sucked into the jar. Why does this happen? When the
fire goes out the air in the jar becomes cold and compresses or gets denser.
Since the balloon does not allow any air to go into the jar, the air pressure is
higher outside the jar than inside the jar and the higher air pressure pushes the
3)
4)
5)
6)
balloon inside. You can let the water out of the balloon with scissors to remove
the water balloon from the jar.
Tell the class that air pressure is measured using a weather instrument called a
barometer. Using the directions provided, make a barometer with the class as a
demonstration. Get as much student input and assistance as possible in
constructing the barometer and discuss how it works as you put it together.
Low and high pressure can be used to make weather predictions. Explain that
low pressure often means cloudy weather with precipitation. High pressure often
means clear, nice weather. Add these ideas to the details about low pressure
and high pressure already on the board, and have students add them to their
science notebooks. A change in air pressure means that the weather is
changing. Discuss your daily weather data with the class. Do they notice any
relationship between the weather and air pressure measurements? Do they
notice any relationship between wind and air pressure measurements?
Briefly, explain that the area where cold and warm air masses meet is called a
front. Ask students what they think might happen when cold and warm air
masses come together? Which air mass will rise? Why? Which air mass will
sink? Why? Explain that when warm air gets pushed up it cools and any water
vapor in the air condenses, creating clouds and precipitation.
Do a simple demonstration to model what happens when a cold and a warm front
come together. Place some oil in a glass beaker. In cup, mix some water with
some food coloring. Add the colored water to the oil in the beaker and observe
the results. Repeat if necessary. Ask the students to explain what liquid
represents the cold front (water) and what liquid represents the warm front (oil).
Discuss as a class. Use the color copies of warm and cold air fronts handouts
provided to discuss these ideas with the class.
Closure: Discuss the following questions with the class. What is air pressure? What
happens to warmer air? What happens to colder air? How can air pressure be used to
make weather predictions?
Assessment: Science notebook responses, participation in class activities and
discussions
Making a Barometer (Demonstration)
A barometer measures air pressure.
Materials:
Balloon
Drinking straw
3’’ x 5’’ index card
Rubber band
Scissors
Metal can
Duct tape
Directions:
1) Cut out a large piece of balloon and stretch it tightly over the open
end of the metal can (smoothly tape the lip of the can with duct tape if
it is ragged). The surface of the balloon should be flat.
2) Attach the balloon to the can securely using rubber bands. Seal the
edges with tape.
3) Lay the straw flat on top of the balloon piece so that one end of the
straw is over the center of the can. Tape it in place.
4) Tape the index card to the side of the can so that it sticks out over the
top (this is used to mark the different positions of the straw).
5) Draw some pencil marks on the index card to indicate high, low, and
medium air pressure readings.
6) Observe the air pressure changes daily (or a couple times a day).
Compare the readings with the barometer from the weather station
and discuss the results as a class. How does the made barometer
work? What happens to the straw when the air pressure is high?
What happens to the straw when the air pressure is low?
Note: The air pressure in the can will be similar to the air pressure
outside of the can. When the air pressure is low, the balloon will rise as
the air molecules in the can spread out. When the air pressure is high,
the balloon will sink as the air molecules in the can become denser.
Cold Front
Warm Front