Partial Design Process These resources engage students in some of the steps in the engineering design process, but do not have them complete the full process. While some of these resources may focus heavily on the brainstorm and design steps, others may emphasize the testing and analysis phases.
Hands-on Activity: Air - Is It Really There?
Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
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By watching and performing several simple experiments, students develop an understanding of the properties of air: it has mass, it takes up space, it can move, it exerts pressure, it can do work.
Engineers must understand the physical properties of air so they can determine the best way to remove pollutants from contaminated air. They study how quickly air moves and how much pressure it exerts. This knowledge helps them design filtration systems that efficiently move air through a system, while at the same time ensuring that pollutants are removed before the air is released into the atmosphere.
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Part B: 1 balloon, and 1 empty one-liter plastic pop or juice bottle (it must have a narrow neck; remove the label)
Demo 2 – Air Has Mass
2 identical balloons
1 meter stick
1 straight pin
Demo 3 – Air Can Move (We Can Feel It)
1 electric fan (table or floor size)
Demo 4 – Air Exerts Pressure (It Pushes on Things)
Part A - Student Activity: 1 sheet of 8.5" x 11" paper per student
Part B - Student Activity: Each student needs 1 straw and 1 small cup containing water
Part C: 1 medium sized jar with an opening smaller than an index card, 1 index card or piece of light-weight cardboard, 1 large bowl/dish in case of spills, paper towels or rags in case of spills
Part D: 1 small juice glass, 1 tissue and 1 medium bowl filled with water
Demo 5 – Air Does Work
1 medium-sized plastic bag
A stack of textbooks
Most of the time, we hardly notice the air around us. We cannot usually see it or taste it. Air does not usually smell (but it does carry substances that we do smell). However, you can feel air when it moves and you can see the effects of air on your surroundings. When air moves, it has great power (to push sailboats, drive windmills and move clouds), and when it is compressed (squashed into a small space), it has great strength (air in a tire supports a vehicle and helps a helicopter to rise into the air).
We must have air to survive. Because of this, engineers work to solve our air pollution problems. There are many things that complicate these solutions, so engineers who work on air pollution problems must have a firm understanding of the composition, properties and behavior of air.
This activity focuses on the physical properties of air: Air takes up space, has mass, can move, exerts pressure and can do work. Engineers need to know the physical properties of air so they can determine the best way to remove pollutants from it. These properties are important to consider when designing a system or process to remove pollutants from the air. Many car exhaust systems, power plant emissions stacks and building systems utilize high-tech filter devices designed to remove pollutants from the air. Some systems that require air to move through pipes can treat only limited volumes of air at a time. Engineers study how quickly air moves and how much pressure it exerts so they can design filtration systems that are strong enough to efficiently move air through the system while still ensuring pollutants are removed before the air is released into the atmosphere.
Before the Activity
The demonstrations go more smoothly if you practice them in advance.
If you have all the supplies organized and ready, it is possible to do all of these demos in one class period.
Part A — Hold up a paper bag and ask the students if there is anything in it. Have the students open the lunch bag and look inside.
Next, blow into the bag and hold the top tight with your hand (see Figure 1).
Question: Ask the students, What is in the bag now? (Answer: Air)
Part B — Push a deflated balloon into a bottle and stretch the open end of the balloon back over the bottle's mouth (see Figure 2).
Question: Have the students guess what will happen to the balloon if you were to try to inflate it inside the bottle. Will the balloon break the bottle, pop or do nothing?
Try to blow up the balloon!
After the experiment, discuss why the balloon did nothing. (Answer: Because air takes up space, the bottle was full of air. When you try to blow up the balloon, the air trapped inside the bottle prevents the balloon from inflating.)
Make the point that even though air is invisible, it still takes up space. Also, discus how engineers need to know how much space air takes up so they can design filtration systems that are large enough to treat the polluted air created by cars, power plants and factories.
Demo 2 – Air Has Mass
Hold up two inflated balloons of the same size attached to opposite ends of a meter stick. Ask the students if there is anything in them. (Answer: Air)
Balance the meter stick such that it is perfectly horizontal, showing that both sides have equal mass (see Figure 3). This may not be perfectly accurate, but it is close enough for the demonstration. Ask students to describe why it balances like this.
Question: Ask students what will happen if you pop one of the balloons. (Answer: They should predict that the end with the inflated balloon still attached will "go down" and the end with the deflated balloon will rise. They can usually relate this to the action of a playground see-saw.)
Pop one of the balloons with the pin.
Question: Ask students to describe what happened and why. (Answer: The side of the stick with the popped balloon rises, because the mass of air in that balloon was released, making that side of the stick lighter.)
Make the point that that even though air is invisible, it still has mass. Why is this important for engineers to study? (Answer: Engineers need to make sure the filtration systems they design are made from materials strong enough to hold the air that is being treated and not break under the weight of the polluted air.)
Alternatively, use a triple-beam or electronic balance, to measure the mass of the balloon before and after it is inflated. What is the mass of the air inside?
Demo 3 – Air Can Move (We Can Feel It)
Talk about air. Can the students see air? How do they know it is there? (Answer: We can feel it moving, for example, the wind.)
Direct an electric fan towards the students and turn it on (see Figure 4).
Ask the students what they felt when they were in front of the fan.
After their responses, explain that what they were feeling was air moving very fast. Explain how the fan makes air move very fast.
Make the point that even though air is invisible, it still can move.
Question: Ask the students to give other examples of when air is moving very fast. Why is it important for engineers to study moving air? (Answer: Engineers need to know how to move air through the filtration systems. A very good filtration system is useless if you cannot get the polluted air to go through it.)
Demo 4 – Air Exerts Pressure (It Pushes on Things)
Part A — Take the students to a place where there is plenty of room to run. If it is a nice day, the activity can be done outside on a playground or in a field. If not, use a gymnasium. At the activity area, pick a few volunteer students. Hand each a piece of 8.5" x 11" paper.
Ask the rest of the class what they think will happen to a piece of paper if the volunteer puts it against his/her stomach while walking forward without holding the paper in place.
Instruct one of the volunteer students to hold a piece of paper against his/her stomach. Have the student let go of the paper when he/she begins to walk forward (see Figure 5). (The paper should fall to the ground.)
Question: Ask the class if they have any ideas why the paper did not stay against the student's body.
Question: Ask the students what they think will happen to the piece of paper if they put it against their stomach and run in a straight line without holding the paper in place.
Select a second volunteer. Have the student place the paper against his/her stomach and hold it with his/her hand.
Tell him/her to begin running in a straight line and let go of the paper when he/she begins running (see Figure 5). (The paper should stay in place.)
Question: Ask the class if they know why the paper stayed in place when the student ran. What caused the paper to stay in place?
Have the rest of the students who want to try it, do so.
Afterwards, explain that the force holding the paper in place when the student ran was air. Make the point that even though air is invisible, it exerts pressure. When you run, the air pushes against you, working to hold the piece of paper against your body. While walking, the paper did not stay in place because the air was not pushing very hard against your body.
Part B — Pass out straws to the students, along with small cups of water.
Allow the students to experiment with the straws by covering the tops with their fingers while withdrawing them from the water. They should note that the water does not fall out of the straws unless they remove their fingers.
Explain to the students that the water does not fall out when the top of the straw is sealed because the pressure of the air outside the straw pushes against the water through the open end of the straw. (If the water were to fall out of a covered straw, a vacuum would be created in the region vacated by the water. Since the vacuum has no pressure while the atmosphere does, the pressure differential keeps the water in the straw against the force of gravity.)
Part C — Question: Ask the students if they think the same result (as Demo 4B) would occur if instead of a straw, they used a container with a larger diameter.
Fill a jar completely with water. Cover the mouth of the jar with an index card. Be sure to get the rim of the jar slightly wet. The best way to do this is to have a slight excess of water on top before you put the card on.
Keeping one finger on the cover, invert the container. Carefully remove your finger. Slowly rotate the jar through a complete circle so the mouth faces up and then down again (see Figure 6). The card should stay on the jar regardless of orientation, showing that air pressure is exerted on the card from the top, bottom and sides.
Part D — Crumple a tissue and push it down into the bottom of a glass so that it does not fall out when you invert the glass.
Turn the glass upside down and place it under the water in a bowl (see Figure 7). Do not tilt the glass. You should find that the water does not enter the glass and that the tissue stays dry.
Question: Ask students to suggest ideas for why the tissue does not get wet. (Answer: Water cannot get into the glass [provided you do not tip it] because the glass is full of air.)
Question: Why is this important to engineers? (Answer: Engineers need to determine how much pressure air exerts so they can design filtration systems that are large enough for all the air to flow through without exerting so much pressure that it breaks the system. Just like when you were running, the air pushed a piece of paper up against you. This same type of pressure is felt by all of the parts of the filtration system as the air moves quickly by. Therefore all of the pieces of the system must be strong enough to not break under this pressure.)
Demo 5 – Air Does Work
Question: Ask students if they can suggest a way to lift a pile of books using only their breath.
Question: If the air is strong enough to push a piece of paper and hold water in a straw or jar, is it strong enough to move and hold books?
Place a plastic bag under the textbooks such that the open end is sticking out slightly. Carefully blow air into the bag, being sure to close the end each time you put in a new breath. The air in the bag should lift the books (see Figure 8).
Question: Ask the students to describe is happening. (Answer: The air in the bag lifts the books.)
Make the point that even though air is invisible, it still can do work.
Question: Ask the students to brainstorm other examples of when air does work. (for example, supporting airplanes, floating hot air balloons, moving windmills, inflating tires that support cars and bicycles, etc.).
At the end, instruct the students to complete the Air – Is It Really There? Worksheet.
Writing: Have the students write a summary about the properties of air demonstrated in this activity. They should include at least one example (either from the activity or discussion) of each of the properties discussed (air takes up space, has mass, moves, exerts pressure, does work). They should also explain why it is important for engineers to study the physical properties of air.
Younger students enjoy these demonstrations. Ask them to draw pictures to show each of the properties of air (air takes up space, has mass, moves, exerts pressure, does work).
Cunningham, J. and N. Herr. Hands-on Physics Activities with Real-Life Applications. West Nyack, NY: The Center for Applied Research in Education, pp. 188-210. 1994.
Environmental Science Lesson Plans. Last updated May 15, 2006. Lesson Plans for Teachers, TCEQ, Texas Commission on Environmental Quality. Accessed September 18, 2006. http://www.tceq.state.tx.us/assistance/education/k-12education/lessonplans.html
EPA NE: Indoor Air Quality – Tools for Schools. April 16, 2004. U.S. Environmental Protection Agency. Accessed October 13, 2004. http://www.epa.gov/iaq/states/nebraska.html
Walpole, Brenda. 175 Science Experiments to Amuse and Amaze Your Friends. Random House, 1988.
Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.
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