Download Adaptation and Behavior

Weather
Lesson #8: Air Pressure and Air Fronts
Time Frame: 45-60 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.
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.
Activities:
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
on the board and discuss it with the class (review density from the matter unit
as necessary).
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 then 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 (gets more dense). 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 pressures pushes the balloon inside. Let
the water out of the balloon with scissors to remove the water balloon from
the jar.
3) Tell the class that air pressure is measured using a weather instrument called
a barometer. Using the directions provided, make a barometer (as a
demonstration) with the class. Get as much student input and assistance as
possible in constructing the barometer and discuss how it works as you put it
together.
2) 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. 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?
3) Briefly, explain that when cold and warm air masses meet (or bump into each
other) this 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.
4) If time permits 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 overhead
or color copies of fronts 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
Resources and Materials: Science notebooks, large glass jar, balloons,
matches, newspaper, large balloons, straws, index cards (3’’ x 5’’), rubber band,
scissors (not provided), metal can, duct tape, glass beaker, cup, food coloring,
oil, water (not provided), front overheads, front color copies