Rocketry has existed for hundreds of years. Although the technology has greatly improved and there are numerous methods for propelling a rocket, the simple science behind rockets has always been the same. To propel a rocket, some kind of force must push it forward. A force is the amount of push or pull on an object. The mechanical force that pushes a rocket or aircraft through the air is known as thrust. In this experiment, you'll make a balloon rocket that is propelled by pressure. Pressure is the amount of force exerted on an area.
When you blow up the balloon, you are filling it with gas particles. The gas particles move freely within the balloon and may collide with one another, exerting pressure on the inside of the balloon. As more gas is added to the balloon, the number of gas particles in the balloon increases, as well as the number of collisions. While the force of a single gas particle collision is too small to notice, the total force created by all of the gas particle collisions within the balloon is significant.
As the number of collisions within the balloon increases, so does the pressure within the balloon. In addition, the pressure of the gas inside the balloon becomes greater than the air pressure outside of the balloon. When you release the opening of the balloon, gas quickly escapes to equalize the pressure inside with the air pressure outside of the balloon. The escaping air exerts a force on the balloon itself. The balloon pushes back in a manner described by Newton's Third Law of Motion. That opposing force—called thrust, in this case—propels the rocket forward.
Balloons
Straws
10 feet of string
Permanent marker
Cargo (paper clips, bottle caps, candy, etc.)
Cereal boxes, construction paper, or any other material to make lightweight cargo containers
Tape, glue, scissors, and any other materials needed for construction
Printed Activity sheet from You Be the Chemist® Activity Guide – Balloon Rockets
Review the information in the Safety First section of the You Be The Chemist® resource guide
As the students perform the experiment, challenge them to identify the independent, dependent, and controlled variables, as well as whether there is a control setup for the experiment. (Hint: As the amount of gas in the balloon changes, does the distance the rocket travels change?)
Have students record data in their science notebooks or on the activity sheet. What happened when the opening of the balloon was released and the gas was allowed to escape? If they timed the process, how long did it take for a rocket to cross the finish line? Have students answer the questions on the activity sheet (or similar ones of your own) to guide the process.
This lesson and activity is part of the Chemical Educational Foundation’s® (CEF) award-winning You Be The Chemist®Activity Guides, a free resource for educators and parents who want to introduce students to chemistry and science concepts in a fun, hands-on manner. The guides feature nearly 1,000 pages of lesson plans, science content, and activity sheets for students in grades K – 8. Download the guides for free at www.chemed.org/ybtc/guides/. CEF’s other programs are the You Be The Chemist Challenge® (a national academic competition for grade 5 – 8 students) and You Be The Chemist® Essential Elements (professional development workshops for educators). In 2014 CEF celebrates its 25th anniversary. Find out more at www.chemed.org.
In this Science Friday video, learn how Raul Oaida, at 18 years-old, attached a LEGO shuttle, a video camera, and a GPS tracker to a huge helium balloon and sent them into space:
Want to learn more about spaceflight? Listen to our Q& A with astronauts Don Pettit and Jeffrey Hoffman:
Newton’s laws of motion have played a key role in humans’ understanding of the universe.
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