Air-Pressure

Air Pressure

Introduction.

Although we do not usually think about it, the air above us exerts significant pressure on us and everything around us. The pressure of the atmosphere at sea level is about 1013 millibars or 101.3 kiloPascals or 760 millimeters of mercury or 14.7 lbs/square inch or 1 atmosphere. Since atmospheric pressure fluctuates significantly with changes in weather conditions, meteorologists use air pressure measurements to help describe weather patterns. Low air pressure often signals stormy weather while high air pressure usually means clear days ahead.

In this lesson students will learn how atmospheric pressure is measured. They will access a weather site to obtain atmospheric pressure readings for various cities across the U. S. and will construct line and isobar graphs.

Audience.

This lesson can be used in an earth science course when discussing weather or in a chemistry course when introducing the concept of gas pressure. It can also be used in a mathematics class when discussing line and contour graphs.

Previous knowledge needed.

Students should have basic Internet skills and should know how to convert measurements using dimensional analysis.

Materials Needed.

Internet access, air pressure worksheets, spreadsheet program or TI-83 calculator or graph paper, U. S. map showing states.

Objectives.

To learn how atmospheric pressure is measured and what units are used;

To convert air pressure measurements such as atmospheres, pascals, millibars, lbs/sq. in.;

To access current atmospheric readings on the Internet;

To create a line graph showing air pressure versus time;

To relate air pressure readings with weather conditions;

To construct a U. S. weather map showing isobars (curves of equal air pressure).

Procedure.

This lesson has two parts. In the first part students access the Internet to find out how atmospheric pressure is measured and to obtain air pressure readings for the past 12 hours from a particular city. They construct a line graph showing the changes in air pressure and make conjectures how air pressure is related to weather conditions. In the second part, students learn how to read an isobar weather map. The class will share air pressure data they obtain from cities across the U. S. and then construct their own isobar map.

Evaluation. See points on worksheets. A short essay describing how air pressure measurements help with weather forecasting can earn extra credit points.

Teacher Notes.

!!!! Warning !!!! The Web sites given in this lesson may have changed! Before using this lesson with your students, be sure to check if the sites are still working or if you must find another site. Sometimes the sites still have the relevant data but you may need to change the directions for accessing the data.

TI-83 instructions:

http://www.ti.com/calc/docs/act/koehler001.htm

http://www.wku.edu/~neal/manual/ti83.html

The Calculator website at the Mathematics Department of the University of Wisconsin-La Crosse will perform basic statistical calculations. If you do not have access to a simple statistical computer package or calculators with statistics options, your students may access http://www.compute.uwlax.edu/stats_htdocs/newmenu.html to perform statistical computations on-line.

In order to print out just a copy of the student worksheet, highlight this section, then copy and paste it into your word processor. You may then revise the worksheet if you wish.

Wisconsin’s Model Academic Standards Addressed.
Science:

A12.3. Give examples that show how partial systems, models, and explanations are used to give quick and reasonable solutions that are accurate enough for basic needs.

C12.3. Evaluate data collected during an investigation, critique the data-collection procedures and results, and suggest ways to make any needed improvements.

D12.12. Using science themes and knowledge of chemical, physical, atomic, and nuclear interactions, explain changes in materials, living things, earth’s features, and stars.

Mathematics:

A.12.1. Use reason and logic to evaluate information, perceive patterns, identify relationships, formulate questions, pose problems, make and test conjectures, and pursue ideas that lead to further understanding and deeper insights.

A12.2. Communicate logical arguments and clearly show why a result does or does not make sense, why the reasoning is or is not valid.

A12.6. Read and understand mathematical texts and other instructional materials, writing about mathematics (e.g., articles in journals) and mathematical ideas as they are used in other contexts.

B12.5. Create and critically evaluate numerical arguments presented in a variety of classroom and real-world situations (e.g., political, economic, scientific, social).

D12.1. Identify, describe, and use derived attributes (e.g., density, speed, acceleration, pressure) to represent and solve problem situations.

E12.1 Work with data in the context of real-world situations by formulating hypotheses that lead to collection and analysis of one- and two-variable data, using technology to generate displays, summary statistics and presentations.

E12.2. Organize and display data from statistical investigations using frequency distributions, percentiles, quartiles, deciles, line of best fit or matrices.

F12.2 Use mathematical functions (e.g., linear, exponential, quadratic, power) in a variety of ways, including recognizing that a variety of mathematical and real-world phenomena can be modeled by the same type of function, translating different forms of representing then (e.g., tables, graphs, functional notation, formulas), describing the relationships among variable quantities in a problem, using appropriate technology to interpret properties of their graphical representations (e.g., intercepts, slopes, rates of change, changes in rates of change, maximum, minimum).

F12.4. Model and solve a variety of mathematical and real-world problems by using algebraic expressions, equations and inequalities.

Social Studies:

A12.1. Use various types of atlases and appropriate vocabulary to describe the physical attributes of a place or region, employing such concepts as climate, plate tectonics, volcanism, and landforms, and to describe the human attributes, employing such concepts as demographics, birth and death rates, doubling time, emigration, and immigration.

Activity Sheets.

Air Pressure (Part I)

Name ___________________

What is atmospheric pressure and how do you think the pressure of the atmosphere can be measured? Access a search engine such as http://altavista.com and type in the questions "What is atmospheric pressure?" and "How is atmospheric pressure measured?" Look through some suggested sites to answer the following questions.

1. (3 points) What is atmospheric pressure?

2. (3 points) Does atmospheric pressure increase or decrease with higher altitude? Explain why.

3. (3 points) What is a device called that measures atmospheric pressure?

4. (3 points) Name three different units that are used to measure air pressure.

5. (1 point each) How are the following units are related?

1 bar = __________ millibars (mb)

1 millibar (mb) = ___________ Pascals (Pa)

1 millibar (mb) = _____________ hectoPascals (hPa)

1 hectoPascal (hPa) = ____________ kiloPascals (kPa)

1 atmosphere (atm) = ____________ millibars (mb) = _____________ hectoPascals

1 atmosphere (atm) = ______________ mm of mercury = ____________ inches of mercury

6. (3 points) Access the site http://www.nws.noaa.gov Click on "Current Conditions" in the left-hand column, then click on a state that you are interested in and finally click on a city in that state. What city did you choose? What sort of weather is being reported in that city for the last few hours?

City _______________________________

Type of weather _______________________________________________________________

7. (3 points) Scroll down and find the air pressure readings for the past 12 hours. Enter these times and pressure readings in the following table.

Time

__________

Air Pressure (hPa)

__________

8. (8 points) Enter the 12 air pressures in hPa from the above table in your spreadsheet or calculator, if available. Make a line graph of air pressure vs time either on your spreadsheet or calculator or on graph paper. Were your air pressure readings generally increasing, generally decreasing, remaining approximately the same, or fluctuating a lot during the last 12 hours?

9. (2 points each) Using your line graph, give a time interval when air pressure was increasing.

Give a time interval when air pressure was decreasing.

10. (2 points) "Normal" atmospheric pressure is defined to be 1013.25 hPa. Were most of your 12 air pressure readings below or above normal?

Number of readings below normal: ______________

Number of readings above normal: _______________

11. (3 points) What was the average of the 12 readings you reported? You can use the average function in your spreadsheet or the mean function on your calculator to calculate this.

Average = ________________

Is this average below or above normal? _____________________

12. (5 points) Share your average air pressure readings and type of weather reported with your class.

Type of weather

Sunny and clear

Partly cloudy

Cloudy, overcast, haze

Some precipitation

Stormy

Average air pressures

______________________________________________________

13. (5 points) Do you see any relationship between average air pressure and type of weather?

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Air Pressure (Part II)

Name _________________________

Use a search engine as http://altavista.com to find out information about isobar maps.

1. (3 points) What is an isobar map?

2. (4 points) Use this pressure and isobar map to answer the following questions.

What is the lowest air pressure reading in the U.S. reported on this isobar map? _____________

Approximately where was this minimum recorded? ________________________

What is the highest air pressure reading in the U.S. reported on this isobar map? ____________

Approximately where was this maximum recorded? ____________________

3. (6 points) Using the isobar map, describe roughly which parts of the U. S. have lower than normal air pressure readings. Remember "normal" air pressure is about 1013 millibars.

Describe roughly which parts of the U. S. have higher than normal air pressure readings.

4. (3 points) Trace the 1012 hPa isobar on the map above which approximately separates the lower from the higher pressure areas of the Unites States.

5. (1 point each) Your teacher will assign you a few states. You should find the current air pressure of a major city in each state. To do so access the site http://www.nws.noaa.gov

*State Assigned*	City Used	Current Air Pressure	Approximate Air Pressure (see below)	Weather Conditions
_____	_______________	_______________	_________________	____________________
_____	_______________	_______________	_________________	____________________
______	_______________	_______________	_________________	____________________

6. (1 point each) In order to make it easier to construct your isobar map, replace air pressure readings in the above table by approximate values using the following intervals:

If the air pressure is

Less than 992 hPa

992 - 995

996 - 999

1000 - 1003

1004 - 1007

1008 - 1011

1012 - 1015

1016 - 1019

1020 - 1023

1024 - 1027

1028 - 1031

1032 or more

then replace it with

988

992

996

1000

1004

1008

1012

1016

1020

1024

1028

1032

7. (10 points) Write the approximate air pressure values found by you and your classmates on this U. S. map in the corresponding state. Connect air pressures that are the same by a curve, thus making an isobar graph.

8. (4 points) a. Which parts of the U. S. are in a high pressure area? Describe weather conditions in these areas.

b. Which parts of the U. S. are in a low pressure area? Describe weather conditions in these areas.

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Air Pressure Part I (Answers)

1. (3 points) What is atmospheric pressure?

The force exerted by the weight of the air above an object or surface.

2. (3 points) Does atmospheric pressure increase or decrease with higher altitude? Explain why.

Decrease because there is less air above you as you climb up. At about 3.5 miles above the earth, air pressure is about half of that at sea level.

3. (3 points) What is a device called that measures atmospheric pressure?

Barometer

4. (3 points) Name at least three different units that are used to measure air pressure.

Millibars, millimeters or inches of mercury, kiloPascals, hectoPascals, lbs per square inch, atmospheres

5. (1 point each) How are the following units are related?

1 bar = _ 1000 ___ millibars (mb)

1 millibar (mb) = __ 100 __ Pascals (Pa)

1 millibar (mb) = ____ 1 _____ hectoPascals (hPa)

1 hectoPascal (hPa) = ____ 0.1 ____ kiloPascals (kPa)

1 atmosphere (atm) = __ 1013.25 __ millibars (mb) = ___ 1013.25 ___ hectoPascals (hPa)

1 atmosphere (atm) = _____ 760 ____ mm of mercury = ___ 29.92 ___ inches of mercury

City ____ La Crosse ___

Type of weather ___ Haze for most of the time followed by mist ___

7. (3 points) Scroll down and find the air pressure readings for the past 12 hours. Enter these times and pressure readings in the following table.

Time Air Pressure (hPa)

6 AM 1013

7 AM 1013

8 AM 1013

9 AM 1013

10 AM 1013

11 AM 1013

12 PM 1013

1 PM 1013

2 PM 1013

3 PM 1013

4 PM 1013

5 PM 1014

6 PM 1015

Remained about the same. Increased during the last 2 hours.

9. (2 points each) a. Using your line graph, give a time interval when air pressure was increasing.

Between 4 PM and 6 PM.

b. Give a time interval when air pressure was decreasing.

Never

10. (2 points) "Normal" atmospheric pressure is defined to be 1013.25 hPa. Were most of your 12 air pressure readings below or above normal?

Number of readings below normal: ____ 10 _____

Number of readings above normal: _____ 2 _______

11. (3 points) What was the average of the 12 readings you reported? You can use the average function in your spreadsheet or the mean function on your calculator to calculate this.

Average = __ 1013.25 ___

Is this average below or above normal? ___ exactly normal_____

12. (5 points) Share your average air pressure readings and type of weather reported with your class.

Type of weather

Sunny and clear

Partly cloudy

Cloudy, overcast, haze

Some precipitation

Stormy

Average air pressures

______________________________________________________

1013.25 _______________________________________________

______________________________________________________

13. (5 points) Do you see any relationship between average air pressure and type of weather?

Sinking air in the vicinity of a high pressure center tends to suppress the upward motions required for the clouds and precipitation to develop, which is why fair weather is commonly associated with an area of high pressure.

Rising air in the vicinity of a low pressure center favors the development of clouds and precipitation, which is why cloudy weather (and likely precipitation) are commonly associated with an area of low pressure.

----------------------------------------------------------------------------------------------------------------

Air Pressure (Part II) (Answers)

Use a search engine as http://altavista.com to find out information about isobar maps

1. (3 points) What is an isobar map?

A weathermap showing lines connecting points of equal atmospheric pressure.

2. (4 points) Use this pressure and isobar map to answer the following questions.

What is the lowest air pressure reading in the U.S. reported on this isobar map? 1000 hPa

Approximately where was this minimum recorded? Vermont

What is the highest air pressure reading in the U.S. reported on this isobar map? 1020 hPa

Approximately where was this maximum recorded? Minnesota, North Dakota

3. (6 points) a. Using the isobar map, describe roughly which parts of the U. S. have lower than normal air pressure readings. Remember "normal" air pressure is about 1013 millibars.

Eastern, western and southern states.

b. Describe roughly which parts of the U. S. have higher than normal air pressure readings.

Upper midwest states.

4. (3 points) Trace the 1012 hPa isobar on the map above which approximately separates the lower from the higher pressure areas of the Unites States.

5. (1 point each) Your teacher will assign you a few states. You should find the current air pressure of a major city in each state. To do so access the site http://www.nws.noaa.gov

*State Assigned*	City Used	Current Air Pressure	Approximate Air Pressure (see below)	Weather Conditions
VA	Charlottesville	1007	1004	Mist
NJ	Atlantic City	1008	1008	Haze
AZ	Flagstaff	1025	1024	clear

6. (1 point each) In order to make it easier to construct your isobar map, replace air pressure readings in the above table by approximate values using the following intervals:

If the air pressure is

Less than 992 hPa

992 - 995

996 - 999

1000 - 1003

1004 - 1007

1008 - 1011

1012 - 1015

1016 - 1019

1020 - 1023

1024 - 1027

1028 - 1031

1032 or more

then replace it with

988

992

996

1000

1004

1008

1012

1016

1020

1024

1028

1032

8. (4 points) a. Which parts of the U. S. are in a high pressure area? Describe weather conditions in these areas.

Answers vary. Weather conditions are more likely to be clear, fair.

b. Which parts of the U. S. are in a low pressure area? Describe weather conditions in these areas.

Answers vary. Weather conditions may be cloudy or stormy.