Water Rocket Design and Lesson

Water Rocket Design and Lesson Plan

The water rocket is among the simplest and yet most exciting ways to simulate a ballistic reaction using safe household materials. The experiment involving the use of pressurized water within a container such as a discarded soda bottle can provide educational insight to young students beginning to learn about propulsion, compression engines, fuel usage and even about the peripheral emphases on taking safety precautions and preparing an experimental design. The Water Rocket is an excellent and engaging way to work with a modestly sized group of students in order to stimulate participation, insight, goal orientation and compliance with a set of specific instructions. The water rocket experiment could also serve as a great way to stimulate creative group activity amongst students.

Design:

The water rocket activity is particularly appealing as a way to examine aeronautics and related subjects in a school setting, mostly because of the simplicity of the design and the capacity of students to conduct research and made their own adjustments based on an evolving understanding of the principles at play. The design itself centers on the use of a few basic objects. The soda bottle is the most common object used to create the vessel itself, and will be filled with water. The nozzle of the bottle should be affixed to a narrow launch tube that fits into the nozzle and continues into the body of the bottle. The launch tube will be used to convey compressed air into the bottle so it must at its most basic be a narrow, hollow and non-porous tube through which the compressed air may pass. The compressed air can be transmitted through a variety of fairly standard and accessible means, including a basic bike pump, an air compressor or a CO2 cartridge.

The passage of the compressed air through the water will cause the air bubble to float to the top of the water mass, instigating a force of pressure that will cause the water to be rapidly ejected from the nozzle once it has been released from the launching tube. Once this reaction has occurred and release has been manually instigated, "the rockets made from these bottles are surprisingly powerful. A standard 2-liter pop bottle 1/3 full of water, pumped to 80 psi and then released, will eject all its water in less than one-tenth of a second, and at that point ("burnout") will be only about 2 meters off the ground. Amazingly, its velocity at burnout is around 76 meters per second. That's over 170 miles per hour." (Johnson, 1)

As per the design of the rocket though, there are a great many steps which the designer can take that will alter the relationship between these various measures. Adaptation to the structure of the rocket can redistribute the emphasis of its flight on distance, duration, speed, trajectory and a host of other variations that render the experiment extremely flexible and open to variable experimentation. As the literature describes on the subject, the use of fins is a common practice which helps to control the flight pattern and produce a more predictable trajectory. Applying a weighted object to the nose of the rocket is also a commonly used technique for improving the stability of the object as it loses the weight provided by the water. The expulsion of this fuel will not only power the rocket in its flight, but will also impinge upon the stability of the bottle as it becomes lighter and more susceptible to interference by the elements. Other common adjustments include the affixing of objects to retain the sturdiness of the structure. According to Johnson (1998), a water rocket constructed optimally can reach up to 300 vertical feet. This is a remarkable distance that can, of course, expose the rocket to damage upon its return to the earth. Thus, other design elements which may be taken into consideration may include rubber bumpers and crumple zones, which can help to lengthen the life of the rocket and make it suitable for repeat launches.

Design Test:

The launch test is the pinnacle of the work conducted by students. Here, the different groups that have designed rockets will test their designs by using the same launch apparatus provided by the teacher. Therefore, it will be the teacher's responsibility to streamline the use of a standard bike pump and the erection of a launch tube, ensuring that this common denominator does not impact differently any group's experimental design.

Using a wide open space such as a soccer field which is not in the direct proximity of any structures or populated areas, groups could affix their respective design to the launch tube and retain it by tethering it to a length of twine. The student selected as the launch captain for each group would stand at a distance of at least 20 feet with the free end of the string at hand while another student from the group, selected as Ground Control, would activate the bike pump. Upon the point at which the compressed air reaches the top of the water bottle and pressure begins to build, the launch captain would release the string, providing freedom for the launch. Launches will be evaluated according to an array of different flight characteristics such as duration, height, stability and perceived velocity.

Lesson Plan:

The lesson plan surrounding this experimental approach is accessible to most demographics, most particularly given that there are few price-based limitations. The materials required cost little money and are accessible to most households. The only limitation will concern the age of students participating. Generally speaking, there are safety considerations that are inherent to this process and these denote that students under the age of 9 or 10 are likely to be too young. This means that grade 5 is likely to be earliest age at which the safety considerations will allow participation. The examination of several key scientific principles such as Newton's Third Law of Motion*, indicates that the experiment is probably most constructive for those in middle school or early high school who are just becoming familiar with these concepts.

The materials required for each group are a two liter soda bottle and materials such as rubber, foam and non-corrosive glue for design variation. The teacher should provide an air pump and launching tube. This denotes the objective for the students to learn concepts of aeronautics and fuel compression while also examining the concepts of experimental design and variable control. The procedure would instigate the latter outcome by pitting groups against one another and asking each group to project its flight expectations based on specific design conditions. Success of each launch would be gauged on its fulfillment of these expectations. Parallels or deviations from these expectations would be subject to student assessment for identification of the factors that caused failure or success.