POP BOTTLE ROCKET
This concept is based on the basic principles of Newtonian physics. Pressure, thrust, fluid mechanics, and aerodynamics are all part of this toy and by learning and using these principles, one would be able to build better rockets.
The way the rocket functions is also quite simple. A regular 2 L pop bottle is partially filled with water. It is then placed open end down on a launch pad. Air is pumped in until a high pressure is reached, then the bottle is released, allowing the pressure to force the water out and produce thrust.
Construction cost would be very low. The launch pad could be made out of durable plastic and the consumer would provide the rockets (bottles) and air pump or compressor. Since the bottles are completely disposable, breaking one or losing one would not be an issue. The only part that may need to be replaced or serviced would be the air valve that fits to the rocket's nozzle and the retaining rod that holds the bottles to the valve. Due to the performance of the rockets, it would be recommended that only 10+ year olds and adults actually launch the rockets, but children down to age 3 or so would be able to design and decorate, as well as enjoy watching them.
Credit for some of the technical information and most of the pictures here should go to the site below.
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Dan Gielas dgielas@andrew.cmu.edu 39-245