Download Weather Unit Lesson

Lesson Three: How Air Pressure Works
Time Frame: 45 minutes
Teacher Objectives: Upon completion of the lesson, the teachers will have:
Demonstrated to students the effects of air pressure and explained how it plays into the
movement of a warm air mass and cold air mass in a weather front.
Student Objectives: Upon completion of the lesson, the students will be able to:
 Explain air pressure, a cold front, and a warm front.
Materials:
For air pressure demonstration:
 2 hard boiled eggs
 1 box of matches
 1 paper towel
 1 small jar (opening large enough for an egg to pass through)
 1 thin wooden board (thin plywood or paneling 2ft. x ¾ in. wide)
Cold Warm Fronts W.S.
 scissors and glue for each student
 red and blue color pencils for each student
Starter: Students fill out their Weather Observations and Weather Charts during the
period before the bell rings and for the first 10 minutes of class.
Activities:
 Opening— The teacher asks students what they think air pressure is. Accept
responses. Then write, “Air pressure is how much air pushes on something” on
the board. Tell students that you are going to show them exactly how much work
air pressure can do.
 Egg in a Bottle (Taken from:
http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/tnrcc/air
pressurelesson.html )
1. Peel both hard boiled eggs just before doing the demonstration.
2. Set a small piece of paper on fire and drop it into the bottle. Place one
hard boiled egg gently on the opening of the bottle, small end first.
The egg may "dance" and wobble on top of the opening. Then, the
egg will appear to be pulled into the bottle after the heated air from
the fire has contracted.
3. Allow the students to explain why the egg went into the bottle.
4. As the air was heated, it began to expand. Some of the air escaped
causing the egg to wobble. When the fire was extinguished, the air
began to cool and contract. The egg seals the bottle. There is less air
in the bottle causing unequal pressure to occur between the air in the
bottle and the air outside the bottle. The greater air pressure on the
outside pushes the egg into the bottle equalizing the air pressure
inside and outside the bottle.
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5. Allow students to explain how you could get the egg out of the bottle.
Keep in mind the first demonstration.
6. Hold the bottle upside down with the small end of the egg in the bottle
neck.
7. Tilt the bottle down until there is a small opening between the neck
of the bottle and the egg.
8. Blow hard into the bottle making a closed seal with your mouth.
Before you remove your mouth, tilt the bottle upside down.
Weight of Air Demonstration:
1. Place one end of the thin board on a table with slightly less than half
the board hanging off the edge.
2. Lay a sheet of newspaper over the part of the board on the table.
3. Allow students to predict what would happen if the protruding end
was struck as hard as possible.
4. Strike the protruding board as hard as you can.
5. The paper will not move. If you hit hard enough, the stick will break.
This is due to the air pressure that is exerted downward. Since the
paper is flat against the board and table, no air is beneath the paper to
counteract the pressure from above.
6. Calculate the surface area of the newspaper. (length by width)
7. Multiply the surface area by 14.5. The result will be the amount of air
pressure exerted on the paper.
8. Have students predict what would happen if you pushed down on the
board slowly.
9. Place your hand on the protruding piece of the board and slowly push
down.
o Have students turn to the next page in their journals and answer the
following questions:
 What do we call the pressure that pushes on all surfaces it
touches.
 Explain how the egg dropped in the bottle.
 Explain why the board did not move the paper.
Cold Warm Fronts W.S. – Tell students that now that they’ve seen how air
pressure is a force that can cause change and do work, we are going to talk
about how air pressure behaves when it is cold or warm.
o The teacher should pass out the Cold Warm Fronts W.S. and allow
students to paste it into their journals. She should then go to the board
and draw two boxes and label one box “cold air” and the other box
“warm air”.
o Draw several circles inside the “cold air” box spaced fairly close together.
Explain to students that at colder temperatures, air molecules are spaced
closer together and don’t move around as much. At colder temperatures,
air molecules don’t have that much energy.
o Draw several circles inside the “warm air” box spaced farther apart with
arrows to show their movement. Explain to students that at warmer
temperatures, air molecules are spaced farther apart and move around a
lot because they have lots of energy.
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o Ask students which type of air
do they think is heavier and why. They should be able to explain that cold
air is heavier because there are more molecules in a certain amount of
space.
o Tell students that just like in the egg in a bottle example where the air
outside the bottle is has greater pressure and pushes the egg inside the
bottle, because cold air is heavier than the warm air, when the two meet,
the cold air pushes the warm air up. Show the illustration of the cold
front on the left side of the worksheet to students and have them color
the cold air mass blue and warm air mass red. Then have them draw an
arrow to show the cold air mass pushing under the warm air mass.
o Explain to students that when a warm air mass has energy and comes up
to a cold air mass, it usually goes over the cold air mass because it’s
lighter, not having as many molecules. Again, tell students to color the
warm and cold air masses on the left side of the worksheet and an arrow
to show the warm air mass going over the cold air mass.
o On the next page in their journals, tell students to write about what
occurs during a cold front and what occurs during a warm front.