Hands-on Activity Building a Barometer

Learning Objectives

After this activity, students should be able to:

• Describe a systems approach that engineers might use to address problems, such as weather forecasting.
• Explain how engineered instrumentation, such as a barometer, can help predict changes in weather systems.
• Relate how air pressure affects changes in weather systems.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• clear bottle with a long, narrow neck, such as an empty and clean ketchup bottle with no lid
• large drinking glass
• ruler
• permanent marker
• Barometer Analysis Worksheet, one per student

Worksheets and Attachments

Pre-Req Knowledge

An understanding of how changes in air pressure are related to changes in weather; see associated lesson 2: Air Under Pressure.

Introduction/Motivation

Wouldn't it be great to be able to predict when a storm was going to arrive in your area? Of course, you could always look at the weather page in the newspaper or internet or watch the TV news; but what if you could just observe the clouds and make a prediction based on your own knowledge of the different types of clouds? Would you be able to make a prediction from this information? How accurate would your prediction be? What other types of things might you need to know to more accurately predict the weather? You may want to also look at the change in temperature, air pressure, wind speed and direction and even humidity.

Weather has many things that affect it. Knowing each of its individual components may help us make more accurate predictions of the weather overall. If we can make measurements and calculations about air pressure, wind speed, temperature and humidity, then we can look at how all of those pieces of information interact to learn about what is really going on with the weather. This way, we can learn about the weather as a system of separate parts that work together. Engineers often look at a problem through a systems approach. They break down a problem into its individual parts, study each part, and then bring what they analyze from each part back together to learn how they interact with each other. Engineers help us do this with weather as well. Engineers design instrumentation that takes measurements of temperature, air pressure, wind and humidity. They design software programs to pull the information from these instruments together and give us a complete description of the weather. When you watch a weather forecast on TV, you are seeing the results of weather instrumentation that engineers have designed here on Earth and in space to help us predict the weather.

We have learned that much of our weather is caused by changes in air pressure. We know that hot air rises and cold air sinks. The rising hot air exerts less pressure on the Earth's surface, so air pressure decreases. Then cooler, dense air, that often carries moisture with it, comes in and replaces the hot air that has risen away. When the air fills with moisture, it releases that moisture in the form of rain, and we have a rainy day. Can we measure air pressure? How do we tell if the air around us is rising or falling?

Well, today we are going to design a weather forecasting instrument to help us predict one change in the system of weather around us. The instrument we are going to make is called a barometer, a device that measures air pressure. Our simple barometers consist of an empty bottle turned upside down in a cup. The wider sides of the bottle rest on the rim of the cup, so that the mouth of the bottle is not touching either the bottom or sides of the cup. Water that we put in the cup will rise to a certain level up the neck of the bottle. The reason that the water rises is that air is pushing down on the water in the cup and forcing it up into the bottle. We call this air pressure. If the air pressure goes up, then it pushes harder on the water in the cup and forces more water up into the bottle. We will be able to measure the change in air pressure by measuring how much the water level in the neck of the bottle goes up or down. If the air pressure goes down, then the air is not pushing as hard on the water in the cup and less water will be in the bottle. The water level in the bottle will go down. Falling air pressure usually indicates that a storm of some sort is approaching. Conversely, rising air pressure is usually an indication that the weather is clearing up.

We will act like engineers as we analyze one individual component of our weather system. What might be our next step if we were trying to help predict the changes in weather around us? Using a systems approach, we might look at other factors affecting the weather system, such as temperature, humidity and wind speed.

Procedure

Background

If a barometer shows that air pressure is decreasing, it indicates a chance for rain very soon. The more rapid the decrease in air pressure, the stormier it will be. The reason decreasing air pressure signals the arrival of a storm is that the decrease in air pressure indicates warm air is rising; the rising air carries moisture with it that forms clouds, and when the clouds fill with moisture, it rains. If the air pressure is increasing, the weather is going to clear up or stay fair.

Before the Activity

• Gather materials.
• Make copies of the Barometer Analysis Worksheet, one per student.
• Ensure that the ketchup bottle when resting upside-down on the glass edges fits in the glass yet does not touch the bottom of the glass (see Figure 2).

With the Students

1. Starting at the top of the neck of the ketchup bottle, have students make a mark every two centimeters, going all the way to the bottom of the bottle (See Figure 2).
2. Turn the bottle upside down and number the marks, starting with "1" at the upside down bottom of the bottle (or, the actual top of the bottle). These numbers do not represent an actual unit of pressure; they are simply to help students measure and compare values.
3. Fill the bottle about half-way with water; hold upright.
4. Place the glass upside-down over the bottle.
5. Quickly flip the bottle and glass over so that the glass is upright and the bottle is upside-down. Some water will spill out, but the water level inside the ketchup bottle should be higher than the level outside of it (that is, inside the glass). If it is not, repeat steps 3-5, using a little more water.
6. Add about an inch more of water into the cup. This ensures that if the pressure increases and pushes more water up the bottle, the bottle opening will remain submerged. Note: The water level in the cup should be just a little higher than the lip of the ketchup bottle. To take a barometer reading, take note of where the water level is inside the ketchup bottle.
7. Place the barometers in a safe place where the temperature stays fairly constant, and where they can be easily observed. They can be stored inside.
8. Record the current water level by using the numbered marks. Record the current weather conditions on your worksheet.
9. Take more barometer readings and weather observations once each day for at least a week. Record the information on your worksheet.
10. Compare any barometer changes to weather changes and look for trends. Were there any changes in weather during the week? Did the barometer change when the weather changed? Did the barometer change without a change in weather? How well did the barometer work? Was the design of your barometer effective? What would you change if you could design the barometer again? How does a barometer help us understand the system of weather around us?

Vocabulary/Definitions

barometer: A device that measures air pressure.

Assessment

Pre-Activity Assessment

Review for Prior Knowledge: Ask the students:

• What causes weather? (Answer: Weather is the result of the movement of air masses that have different pressures.)
• What causes the movement of air masses? (Answer: Different pressures and temperatures of the air cause masses to move; for example, warm air rises.)
• What are some properties of air that can be measured and that can tell us about weather? (Answer: Temperature, pressure and humidity are all properties of air that can help us predict weather.)

Activity Embedded Assessment

Prediction: Ask each group to predict what will happen during the week to the barometric pressure as the weather changes (for example, if it rains outside, what will happen to the water level?).

Observations: Have students record their observations of their barometers on the attached worksheet or in an engineering log (journal). After the week has passed, have student share their observations with the class in the form of a class discussion.

Post-Activity Assessment

Optimize It!: As the class makes barometers, they will be working as engineers. Engineers continuously make improvements on existing devices, such as barometers, that increase the reliability of the instrument. With the class, make a list on the board of ideas that could improve the barometers' functions. What are some ideas for things they could add to their barometers to get a complete picture of how the weather system is changing in their area? Are there aesthetic considerations (the way the barometer looks) that went into the original design of their barometer? Would they change the aesthetics if they could design it again? Would aesthetics take away from the barometer's functionality (how well it works)? When considering all the ways to improve their design, the class will be doing exactly what engineers do as they strive to make increasingly better and useful products.

Troubleshooting Tips

Make sure the mouth of the bottle does not rest on (touch) the bottom of the glass. If it does, the water level will not be able to rise or fall.

When flipping the bottle upside-down, some water may spill out. Make sure that the water level inside the bottle is at least higher than that outside the bottle. If it is not, repeat steps 3-5, using more water the second time.

Activity Extensions

Model the effects of air pressure with an aluminum can. The can keeps its shape because the air pressure inside the can equals the air pressure outside the cup. Try putting the empty can upside down in ice cold water, and notice how the can implodes due to the difference in the air pressure inside and outside the can (That is, as the air in the can gets colder, the air pressure in the can decreases. The higher air pressure from the outside air crushes the can).

Activity Scaling

• For upper grades, have students work in groups of two, which encourages them to better understand the activity. Allow students the freedom to redesign their barometers for more accurate measurements (such as increasing the number of lines on the upside down bottle). Have students graph the barometer measurement data that they collect and then explain any trends in the graph to the class.
• For lower grades, use the permanent markers to draw symbols on the ketchup bottle that can help students remember what the different pressure values mean. Draw a cloud towards the bottom for low pressure, and a sun towards the top for high pressure.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.