Observations and results
How far did your balloon rocket travel?

Even though you did not fill the balloon with rocket fuel, it was able to blast off just like a space shuttle. In fact, the balloon is so light that all it needs is a jet of air to create enough thrust to get it to move through space.

Of course, if you blow up a balloon and let go of the end without sending it along a string, it might zip around in several directions, but it probably won't travel as far in any one direction. Keeping it moving along a string focuses the power from the balloon's air in a single direction, generating more concentrated thrust and helping it travel as far as possible in one direction.

If you have balloons of other sizes or shapes (or even if you just try filling one with more or less air), which ones travel farthest or fastest? You can also try setting up two parallel strings and having balloon races!

What other forms of transportation use thrust? Have you ever seen a hovercraft? It uses a giant fan mounted on the back of the boat, which helps it move forward using only air. Although the fan is powered by fuel, it generates air thrust just like your balloon rocket. Some animals even use the principle of propulsion to get around. Squids, octopuses and jellyfishes, for example, can fill part of their flexible bodies with water and force it out through a smaller opening, propelling them through—and even out of—the water. Humans have studied these natural forms of propulsion to get ideas for our vehicles and technology. Scientists were able to take this simple principle and combine it with knowledge of chemical reactions to create much stronger boosts—like those found in rockets.

Share your balloon rocket observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.

Cleanup
Remove the straw from the balloon if you plan to reuse the balloon (but be careful for weak spots from the tape). Take down the string and reuse it for something else.

More to explore
"Can You Explain How Jet Propulsion Engines Work?" from Scientific American
"Can a Squid Fly out of Water?" from Scientific American
The Space Place site for kids from NASA
"Beginner's Guide to Rockets, Rocket Propulsion Activity" from NASA
Move It!: Motion, Forces and You by Adrienne Mason, ages 4–8
365 More Simple Science Experiments with Everyday Materials by Judy Breckenridge, Anthony D. Fredericks and Louis V. Loeschnig, ages 9–12

Up next…
Talk through a String Telephone

What you'll need
•    Two large paper cups (disposable plastic cups will also work)
•    Two paperclips or toothpicks
•    Length of cotton string or fishing line approximately 10 to 30 feet long
•    Quiet area

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