Methods and Materials

Our Apparatus and Procedure

• Apparatus
  Our rocket launcher needs to perform two functions:
  1) seal and pressurize the water inside the two liter bottle and
  2) release the bottle cleanly and precisely each time the bottle is launched.
  
  To accomplish these two goals we constructed the rocket and launcher as follows:
  The rocket was constructed from a simple 2-liter soda bottle, which we modified by removing the cap and attaching 3 fins at equal distances and angles from the nozzle and each other. These fins were made from 1"x5" pieces of foam board and secured to the rocket with duct tape.
  Our launching apparatus was more complicated. We constructed a three sided base from 4"x6" pieces of plywood with pieces of 2" wooden dowels as legs. This base had a smaller rectangular piece cut out in which we placed the actual launcher. The launcher was made from a similar 4"x6" piece of wood on which we screwed a double switch electrical housing. We drilled a hole with approximately a 1" diameter through which we inserted a jointed piece of PVC plumbing pipe. We mounted a rubber beaker stopper with two holes in it onto the PVC pipe in the electrical house as a seal for the rocket nozzle. On the opposite end of the pipe we epoxied a valve- stem from a car tire for water proof pressurizing. This launcher was then fitted into the larger base and fastened with metal shelf reinforcements which were screwed down with wing nuts.
  
  
  
• Procedure
  For launching, the above-mentioned rocket was filled with a standard 500mL of water measured with a graduated cylinder. The removable launcher was fitted stopper-to-nozzle on the rocket, and then a metal fork with a twine leash was inserted through two holes in one side of the electrical housing, under either side of the lip of the rocket's nozzle and finally in two identical holes on the opposite side of the housing. The launcher was fastened into the base which had been secured to the ground by tent stakes and heavy twine. Then, using an electric compressor on the stem of the PVC pipe, the rocket was pressurized to approximately 70psi, and hence prepared for launch.
  For each launch, one member of the group would pressurize the rocket while another member would concentrate on pulling the fork consistently, and horizontally out. The trials were recorded with a digital video camera operated by a member of the ACE lab. The rocket launcher was placed in front of a 40-foot length of twine, which had been flagged at 3 foot intervals and suspended from a fourth story balcony.