Water Bottle Rockets
What makes rockets fly straight? What makes rockets fly far? Why use water to make the rocket fly? Students are challenged to design and build rockets from two-liter plastic soda bottles that travel as far and straight as possible or stay aloft as long as possible. Guided by the steps of the engineering design process, students first watch a video that shows rocket launch failures and then participate in three teacher-led mini-activities with demos to explore key rocket design concepts: center of drag, center of mass, and momentum and impulse. Then the class tests four combinations of propellants (air, water) and center of mass (weight added fore or aft) to see how these variables affect rocket distance and hang time. From what they learn, student pairs create their own rockets from plastic bottles with cardboard fins and their choices of propellant and center of mass placement, which they test and refine before a culminating engineering field day competition. Teams design for maximum distance or hang time; adding a parachute is optional. Students learn that engineering failures during design and testing are just steps along the way to success.
Water bottle rocket launch at an engineering field day competition.Copyright 2015 Duff Harrold, RESOURCE GK-12 Program, College of Engineering, University of California Davis
Mechanical, aerospace and aeronautical engineers design aircraft such as airplanes, helicopters and space shuttles that must fly reliably, safely and predictably. This requires an understanding of the fundamental laws of physics and strong backgrounds in basic engineering disciplines (dynamics, fluid mechanics, materials). Materials engineers develop materials that can withstand environmental extremes associated with flight. Like engineers, students follow the steps of the engineering design process and apply the fundamental concepts of physics principles to design, test and redesign water bottle rockets that fly as intended.
After this activity, students should be able to:
- Design and build a water bottle rocket that flies straight and in the desired direction.
- Explain center of drag, and center of mass, and draw their relationships to each other for a straight-flying rocket.
- Explain why water is more effective than air for propelling bottle rockets.
- Explain the steps in the design process as they created their rockets, highlighting successes and failures, and suggesting further improvements.