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## Lighter Than Air: Building a Hot Air Balloon | Stem in 30

In this activity, students work in teams to construct a hot air balloon out of tissue paper to demonstrate how a hot air balloon flies. They will develop a conceptual model to explain why the balloon rises when heated.

### Lesson Summary

Lesson Title:  Lighter Than Air: Building a Hot Air Balloon
Timeline:  3-­4 Days

Lesson Overview: In this activity, students work in teams to construct a hot air balloon out of tissue paper to demonstrate how a hot air balloon flies. They will develop a conceptual model to explain why the balloon rises when heated.

### Learning Objectives

• Students will build a working model of a hot air balloon.
• Students will understand the concept that hot air is lighter than cool air, because it has less mass per unit of volume.
• Students will be able to model lighter than air flight.
• Students will be able to describe the difference between hot air balloons and gas balloons.

NGSS Standards:

MS­ETS1­4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

MS­PS1­4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

Crosscutting Concepts: Cause and Effect, Energy and Matter, Structure and Function

Science and Engineering Practices: Developing and Using Models, Constructing Explanations and Designing Solutions

### Supplies

• Tissue Paper (20” X 30”) ­ 21 sheets per balloon
• Glue Sticks
• Stapler
• Cardstock (1 1/2 inch strips ­ enough to make a 10” diameter ring)
• String
• Stapler
• Hot Air Gun

### Vocabulary

Density:​ The measure of how much matter is in a certain volume.
Fluid:​ A​substance that has no fixed shape and yields easily to external pressure; a gas or a liquid.
Pressure:​ T​he continuous physical force exerted on or against an object by something in contact with it.
Gravity: ​T​he force that attracts a body toward the center of the earth.
Gore:​ A sector of a curved surface.

### Learning Activities

Day 1­-2: Build

• Create the template. This can be done in advance to save time.
• Print out the template PDF and tape together, cut along the curved line.
• The template is for half of the gore (each individual piece is called a gore). You will need to fold a piece of butcher paper in half, trace the gore, cut, and unfold it. Do not cut along the fold.
• Transfer the template to cardboard or foam board. (Optional: This is helpful if building multiple balloons.)
• Build the tissue paper panels.
• Overlap sheets of tissue paper by 1 inch and glue together using a glue stick.
• You will need 3 sheets of tissue paper per panel.
• You will need 7 total panels.
• Stack the 7 panels on top of each other.
• Lay the template on top of the panel stack and cut all 7 layers at once.
• Select 2 gores and lay them on top of each other.
• Leave a 1/2 inch margin to the right so gore #2 shows. (Diagram 1)
• Apply a line of glue along the 1/2 inch margin of the bottom gore. (Diagram 2)
• Fold the bottom gore onto the top gore. (Diagram 3)
• Place gore 3 on top of gores 1 and 2 leaving a 1/2 inch margin on the left.
• Apply a solid line of glue along the 1/2 inch margin of gore 2.
• Fold gore 2 onto gore 3.
• Repeat this process for the remaining 4 gores.
• Join the free edges of gore 1 and gore 7. This will create a circle when opened.
• Hint: ​As you glue be sure to occasionally make sure the folds are not sticking together.
• Tie the top of the balloon together using string or ribbon, 1/2 ­ 1 inch from the top.
• Using cardstock and staples create a 10 inch ring.
• Place the ring inside the mouth of the balloon, loop the tissue paper around the cardstock ring, and staple.
• Hint:​You may have to fold the tissue paper together to make it fit snugly around the ring.
• Let the balloon dry completely before launching.
• Patch any holes or rips in the balloon by gluing left over tissue paper over the opening.
• If launching in a place with limited space, you can attach a tether by stapling string to the inside of the ring and securing the other end to the floor.

Day 3: Launch

• With 2 or 3 people, gently pick up balloon and begin to pull folds out to shape the balloon.
• Hold the bottom of the balloon over a heat gun.
• Turn on the heat gun and allow the balloon to fill up and take shape.
• Discussion Question: Why isn’t the balloon flying?
• Turn on the hot air.
• Discussion Question: Why does the balloon fly now?
• WARNING: Heat guns get very hot, use caution when holding the balloon.
• As the balloon begins to pull upward, release and enjoy the flight.
• WARNING: Do NOT launch in the vicinity of power lines!!!
• Have students create diagrams showing what is happening to the air inside the balloon and why it is flying.

Diagram

Discussion Questions

• Why did the hot air balloon float?
• What was happening to the air molecules inside the balloon?
• How could we improve the design of our hot air balloon?
• Using your knowledge of how a hot air balloon flies, can you make a guess about how helium balloons float?
• What would be some advantages or disadvantages to flying in a hot air balloon?
• Why might the hot air balloon be shaped long and narrow, rather than round like a birthday balloon?

Extensions

• Design a basket to carry weights and have students compete to see whose balloon lifts the most.
• Compare the lifting capacity of your hot air balloon to helium balloons.

Resources

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