Pressure in the Atmosphere
Name______________
Class Period _____
Lesson 2A: Atmospheric Thermodynamics
Estimated Time: Two to three forty-five minute class periods
Indicator(s): Core Learning Goal 1
1.4.2 The student will analyze data to make predictions, decisions, or draw conclusions.
1.4.6 The student will describe trends revealed by data.
1.5.2? The student will explain scientific concepts and processes through drawing, writing, and/or oral communication.
1.5.3 ?The student will use computers and or graphing calculators to produce the visual materials (tables, graphs, and spreadsheets) that will be used for communicating results.
1.5.5 ?The student will create or interpret graphics (scale drawings, photographs, digital images, etc.)
Indicator(s): Core Learning Goal 2
2.4.5 The student will explain the dynamic activity of the earth.
Student Instructional Outcome(s):
The student will be able to determine the relationships between pressure and temperature and volume of a gas by developing and conducting experiment.
Brief Description:
Atmospheric pressure is a key variable in weather analysis and forecasting. Pressure centers, lows and highs, are one of the main features on a weather map, and their intensity and path relative to where we live determine many components of our weather.
Background knowledge/teacher notes:
The Gas Laws
The gas laws relate temperature, pressure and volume in an ideal gas (where the attractive forces between molecules are not taken into account). Volume refers to the space occupied by a fixed volume of gas molecules. Density is the inverse of volume.
According to Boyle's Law, pressure is inversely proportional to volume. The product of pressure and volume is a constant.
Pinitial Vinitial = Pfinal Vfinal
If gas pressure is held constant, there is a direct relationship between temperature and volume. An increase in temperature results in an increase in volume. Charles' Law may be written mathematically:
Vinitial = Vfinal
------- --------
Tinitial Tfinal
Boyle's Law and Charles' Law may be combined mathematically as follows:
Pinitial Vinitia = Pfinal Vfinal
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Tinitial Tfinal
This lesson leads up to later lessons concerning weather systems and patterns. It assumes the students have had basic concepts of temperature, pressure and density in middle school or other high school courses. The overview on pressure will bring all students to the same basic level of understanding on key background concepts pressure.
Provide a demonstration of the effects of temperature on pressure by inflating a rubber balloon and tying the end closed. Have a student measure the maximum dimension of the balloon by holding it next to an upright meter stick. Record this dimension on the board in centimeters. Then, use an electric hair dryer (not too close to the balloon!) and heat the air inside the balloon for about 1- 2 minutes. Repeat the measurement of maximum dimension. Ask students why the balloon increased in size! (Some will be convinced you "blew" air into the balloon!)
Challenge the students to devise an experiment to actually measure this effect. First, however, show them the equipment listed below in the materials section and explain how it might be used in the experiment. Students will need practice manipulating CBLs and probes and using the graphing calculators in analysis. Many students will build on their knowledge of graphing calculators and CBLs from use in mathematics class.
Following the activity sheet, a brief overview of concepts of pressure is provided
The final phase of this lesson is a student directed investigation. Students are challenged to develop a device to measure the relationship between pressure in a closed container and the experiment temperature of the gas (air) in this container. Their report sheet/journal entry is to contain a data table of measured temperatures and pressures (or force), and a graph of the relationship. There are several ways this experiment can be accomplished — one set-up is explained.
As an extension, students are asked to apply what they have observed/measured/learned from their laboratory experiment to the science of meteorology, specifically, the relationship between air temperature and atmospheric pressure.
In the set-up demonstrated above, the pressure sensor is placed directly against the flat cardboard disk that is resting on a piece of plastic wrap (e.g. "Saran Warp") stretched TIGHTLY across the glass jar. The thermometer sensor is placed inside the jar, with the point where its wire leads out of the jar carefully smoothed out with clay so that there is no leakage out of the jar at this point. It will be important to zero the pressure reading and establish a baseline temperature before heating the jar. The students should set up the CBL to collect data from both sensors at approximately 5-second intervals for a total of 2-4 minutes. The jar is then heated by holding a hair dryer hot air stream against it or by placing it on a hot plate on the LOWEST setting. Students need to wear safety goggles when performing this experiment due to the possibility of glass breakage. Results can be viewed graphically on the graphing calculators or printed out in table form for manual graphing and analysis.
The readings will show a relationship between temperature inside the jar and pressure exerted by this increased temperature. Use of a barometer sensor inside the jar will provide a direct pressure reading, use of the cardboard disk and the pressure sensor show an indirect measure of the air pressure as it acts on the plastic wrap.
Students should determine the relationship between temperature and pressure, using graphs or data tables, and they should attempt to define this relationship in words (i.e. "directly proportional" or "inversely proportional") and a mathematical expression. Note that the experiment above holds the "volume" variable at a constant value (the glass jar doesn’t expand, and the plastic wrap is tightly stretched). Another variation of the experiment would be to cover the jar with a balloon and heat the jar. The balloon will expand and the students are challenged to determine a mathematical way to measure this. The expansion is roughly spherical if a spherical balloon is used — the volume of a sphere is 4/3 p r3, where r goes from 0 when the balloon in lying on its side to the radius of the inflated balloon after heating and expansion.
Lesson Description:
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ENGAGE |
The weather channel is always talking about "highs" and "lows" on the weather maps. What are these things? Why do they have an affect on our weather? If we had to "order up" some highs and lows to create a snow day, what would we order, and where would we put them on the map? Highs and lows are areas of different "pressure". What is meant by pressure? Some related terms in meteorology are "density" and "volume". Ask students to work in small groups to come up with some definitions of these terms. Ask students to consider: Is pressure related to other things we hear on the weather report, like temperature and wind? Students will complete Activity Sheet 1 (attached) which steps them through basic definitions of volume and density, and then has them calculate the density of a wooden block and the density of a basketball or volleyball. The basketball density is re-calculated after the students pump additional air into the ball, and students provide an analysis of the change. Education Elements: SCIENTIFIC TOOLS SEES figure 2.03; line graph showing pressure and density vs. altitude. http://see.gsfc.nasa.gov/education/SEES/strat/class/Chap_2/2_Js/2-03.jpg |
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EXPLORE |
Design an experiment to investigate, using a CBL (Calculator-Based Lab) and graphing calculators, how pressure can be measured in an experimental setting, and its relationship to
Accommodation: Provide a lab sheet with steps to be followed, a place to record data, and steps to follow to use the graphing calculator. For levels 1-2, write lab as a class or use as a demonstration. Educational Elements: EDUCATIONAL TOPICS "Equation of State" fact sheet with links on ideal gas laws http://www.grc.nasa.gov/WWW/K-12/airplane/eqstat.html |
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EXPLAIN |
Journal Write :Summarize you experiment, including the following sections:
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EXTEND |
How else can we conduct this experiment? What would be the advantages and disadvantages of other possible experimental set-ups? Create a complete experiment design, including the set-up of the equipment and the sensors, which will allow us to do this. GT Connection: Investigate the gas laws used by chemists. Think of the formulas as mathematical models. Use the formulas to relate the outcome of your experiment to a mathematical model. Education Elements: BACKGROUND INFORMATION SEES text, chapter 1, sections 2.2 and 2.3, describing vertical structure of the atmosphere. http://see.gsfc.nasa.gov/education/SEES/strat/class/Chap_2/index.htmModification: The Extend section could be deleted for some groups since it is not essential to meet the outcomes for the lesson. |
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EVALUATE |
Use a scoring tool or checklist to evaluate the lab write-up. |
Materials:
Activity Sheet: Pressure in the Atmosphere
CBL (Calculator-based Laboratory)
Temperature probe
Force sensor (ideally with 0-5N range)
Barometer sensor
TI Calculator (TI-82/83 or 83 plus/85) and sensing programs (available for free download from
http://www.ti.com or http://www.vernier.com; TI-83 "plus" calculators have the programs built in already)Ring stand (to hold pressure sensor)
"C-clamp" to hold ring stand to table
Masking tape
Glass jar or flask (have students bring in an old spaghetti sauce bottle). Plastic containers will not work.
Balloons
Rubber bands
Clay to seal container around wire
Safety goggles for every student
Heat source
Resources:
Background information on pressure available:
University of Illinois W2010
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/prs/home.rxmlPressure Activity
University of Illinois W2010.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/prs.rxmlEither of these could be used as material supplemental to this lesson, but are not required.
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Pressure in the Atmosphere Name______________ Class Period _____ |
This lesson uses the term "pressure". Write a definition of pressure (as used in science) in your own words:
The term "volume" is also used. What do we mean by the "volume" of a container?
You have used the expression "density" in other science courses. A soccer ball and a bowling ball have approximately the same volume — they take up about the same amount of space. However, one is significantly harder to pick up than the other. Why? (Use the idea of density in your answer!)
A block of wood has dimensions 5cm wide by 10 cm long by 4cm tall. What is its volume? What units do we describe volume with?
If this wooden block has a mass of 400g, what is its density in grams per cubic centimeter (g/cm3)?
The volume of a sphere is given by the mathematical expression
Measure the diameter of the ball, and divide by two to get its radius. Record it here __________cm
Measure the mass of the ball by standing it on the scale. You may have to use a very small piece of tape to keep it from rolling off! Record its mass here __________ g
Calculate the volume of the sphere using the equation above. Record you answer here _________cm3
Calculate the density of the sphere. Since the units of density are g/cm3, you should be able to figure out how to do this! Record you answer here __________ g/cm3 . Realize that this is the "average" density of the ball, but it is mostly air inside it!
Now use the hand-held pump and add more air. Make the ball quite firm, but don’t pop it! Measure its mass again, and calculate its new density. If you think the volume changed because the ball got bigger, you’ll have to recalculate volume again as well. Record the new density here _______g/cm3
Was the new density different? Why or why not?