Hot air balloons and other flying balloon contraptions are a source of fascination for many children. Every year here in St. Louis, the Great Forest Park Balloon Race captivates and inspires wonder for many a child. But how do those balloons work? That’s the exact question, from a third grader at the information desk one day, that inspired this latest school-age science program, Balloon Science.
First, we talked about the history and science. I introduced the history of air balloons, from ideas of flying in ancient Greece to the first balloons by the Montgolfier brothers in the 18th century. We also talked a bit about a more recent use for these sorts of balloons in 20th century history: Japanese balloon bombs set across the Pacific toward the west coast of the United States during WWII. Two great books touch on this little-known historical topic: 2013’s Courage Has No Color by Tanya Lee Stone offers the nonfiction perspective, and 2012’s Jump into the Sky by Shelley Pearsall gives a historical fiction angle.
Next came the science behind how these balloons stay aloft. First we talked about the hot air balloons that are most familiar to most children. Using about six different nonfiction books from our stacks, I described and showed pictures of the various parts of hot air balloons: the envelope (what we think of as the balloon) and its construction of nonflammable materials; the flame to heat the air; the control cord and vent that allow for some navigability; and the basket for the passengers. We talked about how these parts work together to allow hot air balloons to fly, the flame heating the air inside the envelope and causing it to rise. We also talked a bit about the imprecise art of steering hot air balloons.
We touched, also, on other methods of making balloons rise in the air: namely, through use of gasses less dense than the air surrounding the balloon. We talked about different gasses being heavy or light, and we talked briefly about the Hindenburg. After all, what kid can resist a real disaster story?
Next, we explored the science behind air balloons through a series of visual demonstrations. To demonstrate the way hot air balloons work, I set up a basic toaster with a cylinder of poster board surrounding it (so nothing could come in contact with the hot toaster exterior). After turning the toaster on, I set a plastic garbage bag over the toaster and cylinder with the open side down. This activity allows children to see how the bag seems to blow up and expand as the air inside it becomes warmer than the outside air. When the amount of warm air inside the bag reaches a certain point, the “balloon” rises from the toaster and flies–at least until warm air begins to escape through the large bag opening. For a great demonstration, use different sizes of trash bags to illustrate why the envelopes of hot air balloons are so big in comparison to their cargo.
I also demonstrated the difference between balloons filled with regular air–i.e., air blown into it by a person–and balloons filled with helium. This is a difference with which most children are already familiar, but the demonstration allows opportunities for talking about density and gasses.
We ended with science in action as the children created their own flying balloons. I got enough mylar helium balloons for every participant (most dollar stores will fill mylar balloons for a dollar a pop), and as I handed them out, I explained that it was the kids’ task to create a basket for a miniature passenger that would be light enough for the balloon to still fly. Several types of supplies were available for experimenting with balloon basket construction: paper, recycled plastic containers, drinking straws, yarn, ribbon, tape, and scissors. The initial creations of each child were too heavy; their balloons were firmly tethered to the ground. As I navigated the room to help prompt solutions to this problem, however, I saw children shedding weight from their baskets in a variety of creative ways. By the end of the program, balloons with baskets were floating drowsily about the room.
Resources for further exploration of balloons were available for checkout. In addition to the resources I used to show pictures of hot air balloon parts, I also set out a variety of nonfiction and fiction books and DVDs that included balloons in some form or another. Everyone got to take home their balloons, too, providing an opportunity for seeing what the cold winter air would do to a helium balloon on their way home.
Have you incorporated balloon science into any of your programs and activities?