• Understand the use and function of a barometer.
• Understand the relationship between weather and changing air pressure.
• Understand the concept behind the design of a basic barometer.
• Develop an appreciation of the complexity of weather and changing weather patterns.
• Develop an appreciation of how changing weather affects everyday life.
1. Following directions
4. Drawing Conclusions
Materials (for each pair of students)
A barometer is an instrument used to measure air pressure. One way air pressure is measured is in inches of mercury. Air pressure is highest as sea level, making the air also heaviest.
At sea level, air pressure is 29.53 inches of mercury. This means that at sea level, it takes 14.7 pounds of pressure per square inch of air to raise mercury in a hollow tube to 29.53 inches in height. What is 14.7 pounds of pressure? Try pushing down on a scale at home until it reads “14.7.”
You have exerted 14.7 pounds of pressure on that scale!
A barometer is an instrument that measures the pressure of the atmosphere at a particular location. There are two types: a mercurial barometer, which uses mercury, and an aneroid barometer that uses a balloon, that expands or contracts when the atmospheric pressure changes.
You may not notice in your experiment that the barometer reading changes in response to temperature as well as direct changes in pressure. Temperature changes pressure, but only in a tightly sealed space (your classroom is not tightly sealed to the outside.) Warmer air taking up the same amount of space as cold air will create more pressure. This is because warm molecules push away from one another instead of moving towards one another. The warm molecules try to take up more space than they have, creating a greater pressure pushing out of the container.
Measuring atmospheric pressure is very important for predicting and preparing for storms.
Barometers allow weather forecasters to estimate maximum hurricane wind speeds. Since air is always flowing from high pressure toward low pressure, air moves inward toward the low pressure center in a hurricane. By using a barometer to find the pressure in the center of the hurricane, forecasters can estimate the fastest wind speeds that the hurricane is capable of producing.
Usually, when barometric pressure (or, pressure as shown on a barometer) falls rapidly, it means a storm is coming. A steady barometer shows stable, fair weather. The barometer saves lives since it helps predict the approach of poor weather. Back when RADAR and satellites didn’t exist, crude barometers were the main way people predicted the approach of bad weather like a hurricane or a major snow storm.
Begin by assessing what students know about barometers and high and low pressure. Make sure to go beyond merely asking what the words mean. Ask about the relationship between these terms, accept examples, and allow students to build off of each other's ideas rather than addressing their thinking to you alone.
The key points are as follows:
1. Barometers measure the air pressure. Air pressure is a good indicator of changing weather patterns.
2. Low pressure means that bad weather is on the way: rain or storms or clouds.
3. High pressure means that good weather is on the way: sunshine and fair days.
The word barometer is derived from the Greek words for weight and measure. Use this as opportunity to practice word dissection. The following questions can help you guide students in making meaning:
Give each student the instructions for making a barometer. It is important to also review the materials as this provides context for the directions.
Engage the students in a discussion concerning why we are using these materials to make the barometer. Show them the balloon and ask them about its properties.
PRE-LAB TEACHING STRATEGIES:
1. Demonstrate that air actually has pressure (or takes up space) by blowing up a plastic baggie and sealing it to the mouth of a jar with a rubber band. Hold the outside of the bag where it is attached to the jar and have a student try to push the baggie into the jar. Discuss with the students that the air pressure inside the jar prevents them from being able to push the baggie in- something’s already there!
2. Initiate a discussion about pressure. Why do your ears hurt when you dive deep into a pool?
Does air weigh anything? Why don’t we feel air pressing down on us? Why does air push out of our ears making them “pop” when we go up in an airplane? Here is a link that explains the physics of these phenomena.
3. Discuss pressure in general with your class. Other than air, what other things exert pressure?
The key points are as follows:
1. Balloons respond to air pressure and can directly indicate how much air pressure there is around them.
2. Get the students to think about why the seal would be airtight? What would happen if there were air in the jar (the balloon would not respond the pressure)?
3. Have the students make predictions about how the balloon will react to the pressure. Get them to discuss why they think this way. Have them give you a specific scientific reason. Then, write down some of their predictions.
Have the students work in pairs to make the barometers.
When students are making the scale, make sure they note that the changes in pressure are small so they will need cm and mm units on the scale bar.
Make sure that you walk around and check that the balloon or plastic wrap is stretched as tightly as possible, being careful not to tear the material. This will help insure more accurate measurements.
Note: You can use balloons or clear plastic wrap. See the images below for samples of student barometers.
1. If you use plastic wrap, have the students be careful not to tear it.
2. Stress that the balloon needs to be stretched as tightly as possible over the mouth of the can or jar.
When the air pressure is greater outside the can, the air will press down on the plastic wrap causing the straw to point up. When the air pressure is greater inside the can, the air inside the can will push up on balloon or plastic wrap and the straw will point downward.
Explain that they will measure pressure changes from the starting day and compare this with actual daily barometric pressure data. Assign/seek volunteers to get data daily (National Weather Service, Weather Bug or other apps, use an aneroid or digital barometer, etc).
Since pressure can be measured in multiple ways (inches of mercury, atmosphere, millibars, kilo-Pascals) you may want to choose the unit(s) to report out. In my class we use both millibars and inches of mercury as these are common on most aneroid barometer. Millibars will be useful when we look at isobars on weather maps in a future lesson.
And most critically, have the students record barometric pressure from their devices daily, inside and outside each day for 1-2 weeks.
Discuss the experiment and how easy or difficult it was to make the barometer.
Discuss with the students how their barometer will work:
Discuss with the students who might use a barometer in their work: gardeners, pilots, coast guard, event planners, meteorologists, and many others.
Help students transfer their learning and push student thinking further by raising new questions and trying these extensions.
To evaluate their work:
1. Were the students able to follow the instructions?
2. Did they understand the basic design? Did they reflect this in their discussion?
3. Could they work in groups to complete the project or did it present challenges to the group?
4. Did they have enough background knowledge about weather?