Hot Air Balloons

One of the first things I suggest to teachers when it comes to choosing a phenomenon is, "write the explanation you would want students to write." The reason for my suggestion is two-fold. First, it allows the teacher to think through the event completely. Second, after thinking through the details of the explanation, teachers also determine which other concepts students need to understand in order to compose a complete explanation. Keeping that in mind, I am updating a project my 8th graders have engaged in for the past 8 years, 3-meter tissue paper hot air balloons, to make the learning more three-dimensional.

The Saturday morning launch, overlooking Prospect Lake, in downtown Colorado Springs. Photo Credit: DarlAruthurS, August 31, 2008.

The Explanation

Hot air balloons work because of the properties of gases. A gas has no definite volume and takes the shape of the container. These properties are due to the properties of the particles of a gas. There is at the best a weak attraction between the particles. The particles fly about and collide with each other as well as the walls of the container.

To heat the air of the hot air balloon, we put charcoal in a pail and a grill plate over the pail. Once the charcoal is lit, and the embers are hot, a chimney is placed over the grill. As air particles collide with the embers, there is heat transfer from the embers to the air. When heated, energy is added to the particles of the gas causing the particles to move faster increasing their kinetic energy. Particles moving faster are more spread out making the volume of the gas more. If the mass of the gas remains the same and the volume increases, the density of the gas decreases. Once the density of the gas is less than the air surrounding the hot air, the air will rise and fill the tissue paper balloon.

The pail with a chimney and a tissue paper balloon is a semi-closed system. Within the system, a convection current is set up as the air of the balloon is heated. As described above, the hot air rises because it is less dense than the surrounding air. Cooler air replaces the leaving hot air and the process repeats. Once the balloon is filled with hot air, there is a tug which indicates the balloon is ready for release. The tissue paper balloon, filled with less dense air will rise until the air cools which increases its density and cause it to descend.

Model of the pail with the chimney on top. The callouts demonstrate a microscopic look of a tiny area within the system. The air closer to the hot embers has longer arrows because the air particles are moving faster with the energy from the embers. The air closer to the top of the chimney is cooler for the time being which is why it has the shorter arrows because the particles are not moving as fast. As time goes, the air will be hotter throughout the system.

Directions: Build the Gore Template

  1. Tape together enough newspaper sheets to cover at least 10 feet.

  2. Draw the 15 cm line at the bottom of their newspaper sheets. To draw the 15 cm line, find the center of the newspaper sheet (our newspapers were approximately 56 cm across, so 28 cm was the center point).

  3. Draw the line so that 7.5 cm of the line is on one side of the center (to 20.5 cm mark on the meterstick) and 7.5 cm is on the opposite side of the center mark (the 35.5 cm mark).

  4. Measure 1.5 meters from that 15 cm line and draw a second line that is 50 cm in length. Follow the same procedure as the 15 cm mark in terms of making certain the line is centered.

  5. From the 50 cm line, measure another 1.5 meters and draw a dot at the center of the newspaper sheets.

  6. This leaves lining up meter sticks to draw a straight line from one side of the 15 cm line to the same side of the 50 cm line and repeating the process on the other side of both lines (see Figure 1).

  7. On one side of the 50 cm line, draw a line that is perpendicular (straight up) 51 cm and on the opposite side a line that is perpendicular 30 cm. From the endpoint of both lines, connect them at the center point that was marked at the top of the template.

  8. At this point, cut out the template.


The Tissue Paper

  • Students that use tissue paper that is 50.8 cm x 66 cm in size only need 5 pieces to make the length that is 3 meters long.

  • Students will need 10 lengths of 5 pieces of tissue paper.

  • To help students conceptualize how to create a pattern, I discussed their options.

    • If students make a gore all of the same colors, they can create vertical stripes.

    • Gores that have a consistent pattern such as red – yellow – blue – yellow –red will create horizontal stripes.

    • Lastly, patterns such as red- yellow- red- yellow- red, then yellow – red- yellow-red – yellow will create a checkerboard effect.

  • It is important for students to check and make certain that their tissue paper is as wide or wider than the template at its widest point, or adjustments need to be made to the template.


Putting it Together

  • Once all ten gores are cut, have students remove the template and keep the tissue paper gores together in a neat stack.

  • Offset the top gore by about 2.5 cm.

  • Using a glue stick, one student needs to run a line of glue down the side of the gore that is the top layer.

  • A second student should be following the student that is gluing and folding the second gore layer over the edge of the top layer.

    • If students are working in groups of four, have two students gluing, one student at the point of the gore, the other at the baseline, and work toward each other.

    • Each student gluing has another student following and folding the second layer over the top layer. This is making the seams of the balloon so it is important to make certain that the folds stick.

  • Once the first side is glued, a student should fold the top layer over and offset layers two and three of the opposite side.

  • Students follow the same procedure as before, but this time, layer three is folded over the top of layer two. After this side is completed, students switch sides but use layers three and four (think accordion).

  • This pattern continues until all of the layers are finished.

  • When ready for the last layer, have students unfold the bottom layer to where it sticks out. Students will then unfold the top layer and match the two layers up to where the bottom layer is slightly outside the top layer. Use the same process, but this time, the bottom layer is folded over the top of the top layer.


Finishing Touches

  • Students need to twist the points at the top of the balloon, tie a string around the points making certain there is a loop in the string.

  • This loop will be used to hang the balloon.

  • Hang the balloons from the ceiling in my classroom.

  • A wire coat hanger fashioned into a circle needs to be added to the opening of the balloon.

  • Roll the tissue paper over the coat hanger and use tape to secure it.

  • The hot air balloon can be tested for holes and leaks using a hot air popcorn popper to inflate the balloon.