Academic journal article Science Scope

Engineering Seltzer Rockets

Academic journal article Science Scope

Engineering Seltzer Rockets

Article excerpt

Building and launching model rockets is an intrinsically interesting and exciting way for students to learn in the contexts of science, technology, engineering, and mathematics (STEM). Ever since Sputnik first turned the attention of a generation toward the exploration of space over half a century ago, thousands of elementary, middle, and secondary instructors have incorporated various aspects of rocketry into their curricula (Napier 2015).

Unfortunately, purchasing a commercial model rocket for every student is beyond the means of many classrooms. Furthermore, such rockets are propelled by dangerous combustions, and their performance is sensitive to even small changes in design, materials, and construction. This limits their pedagogical value, because students cannot safely or easily plan, construct, and evaluate their own vehicles and engines. These problems can be avoided, however, with more tranquil chemistry.

This article describes an activity in which students test and refine seltzer rockets--film canisters powered by effervescent tablets. This simple and low-cost method allows students to explore and improve the propulsion of legitimate rockets. In doing so, students also develop core understandings and practices in science and engineering identified by the Next Generation Science Standards (NGSS).

Materials, performance, and science of the seltzer rocket

To launch a seltzer rocket, at least one-quarter of an effervescent tablet and just enough water to cover it are placed in a 35 mm film canister. A tight-fitting lid is quickly secured and the canister is turned over so the lid serves as the rocket's base. The water dissolves the tablet, allowing sodium bicarbonate and citric acid in the tablet to react, generating gaseous carbon dioxide. As more C[O.sub.2] is produced, the pressure it creates within the canister builds until the lid can no longer contain it. This process can happen almost instantaneously or over a minute or more, depending on several factors (e.g., the temperature of the water).

When the gas finally pushes the lid out of the way, it also propels the canister upward, obeying Newton's third law and acting just like a rocket using a combustible fuel. However, unlike traditional rockets, seltzer rockets can be safely launched indoors. More importantly, because its performance is influenced by several easily observed and manipuated variables, the seltzer rocket is an excellent vehicle for developing students' understanding of motion, forces, and energy, as well as investigational and engineering skills.

Engaging students in engineering seltzer rockets

There are many strategies for engaging students in the designing, building, and launching of rockets. One way to do this is to show them short videos of rockets being launched, including those used to lift people, equipment, and supplies into orbit, as well as much smaller models of real and imagined rockets built and launched by rocketry enthusiasts (brief descriptions of suitable videos can be found in the online supplements at www.nsta.org/middleschool/connections.aspx). In addition to a great "hook" and introduction to the activities that will follow, this provides an opportunity for teachers to strengthen students' understandings of models, particularly how model rockets differ from the devices they are sometimes used to represent.

It is important to introduce the concept of engineering at this point, because that process is integral to this activity. Begin by sharing some illustrations and photos of famous rockets and how they have changed over time (see the online supplementary materials for a guide). To stimulate students' thinking and conversations, ask them to write answers to these questions:

* How have rockets changed over time?

* Why do you think rockets have changed over time?

* What do we call the people who have worked to change rockets over time? …

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