Step 1: First Step: the Most Obvious Part
Step 2: Step 2: Gathering the Materials
Step 3: Numero Tres: What to Do With the Second Bottle.
Now your probably asking yourself, what's with the other bottle? Well now I will explain. You will take the bottle (not the coke bottle) and cut it in half. The top half will be trimmed up to where the bottle begins to curve toward the neck and the opening. Then the Opening (the part that the cap screws on) should be cut off and discarded, along with the bottom part of the top half of the bottle.
After successfully trying to decipher my instructions, you will end up with what you see in the pictures. You, the will then take the other bottle, the one you are going to use as the fuselage of the rocket, and precede to tear off the label. After doing so, you will then attach the bottom half of the bottle you cut on to the bottom of the bottle. Use the level to make sure it is even before securing it with masking tape. Take the cut top and then attach it to the curved portion of the fuselage before securing with tape. Then continue by wrapping the bottle in duct tape. Doing these procedures will strengthen the integrity of the bottle so that the pressure will not cause the bottle to explode easily.
Now you may start doing Step 3. If you are done, please proceed to the next step.
Step 4: Step 4: Fins
Okay, now on to the instructions. In order to lessen the amount of resistance on your rocket, your fins should have a length of 22 cm and a width of 9 cm. This should give you a shape of a long right triangle. Measure and cut out four of these fins. Once you cut them out, take your trusty X-Acto knife (don't cut yourself accidentally) and with the long side of the fin, slice about two corrugations into the fin. This should allow you to open up the fin itself and create a base in which you can attach the fins to the bottle without much incident.
After performing this step with the X-Acto knife, attach the fins to the bottle through the use of the duct tape. Make sure the fins are straight and spread out evenly along the rocket. When you are content with the fin placement, your rocket should look like the rocket in the picture below. When done, move to step 5.
Step 5: Step 5: the Parachute
After tape placement, take a roll of nylon string and cut five pieces of equal length. In order to prevent frayed ends, use a lighted match to melt the ends of the strings. Punch holes into the tape on the parachutes then proceed to tie the strings to the parachute. Attach your parachute to the rocket or your tennis ball, and voila! You have a working parachute.