A water bottle rocket uses air pressure and water to launch the rocket into the air. When air is pumped into the water bottle, and the pressure gets too high, the liquid needs to escape. The air and water explode out of the mouth of the bottle, and the reaction from the water hitting the launcher and ground makes the bottle fly into the air. Some water bottle rockets can fly 30 feet or higher into the air.
Cut off the top four inches of a water bottle. Tape this over the bottom of a second, uncut, water bottle to make a nose for the rocket. Push a small lump of play dough into the nose of the cut bottle to add weight.
Cut four 4-inch-long triangles from craft foam to make guiding stabilisers for the rocket.
Tape the triangles around the top half of the water bottle. Make sure one long side of each triangle faces down when the bottle is turned upside down.
Using the pipe saw, cut one 4-inch section, two one-foot sections, and one 3-foot section from PVC pipe.
Drill a hole in the centre of one end cap large enough to fit the valve through it. Using bathtub sealer, glue the valve inside the hole with the stem facing up.
Connect the two one-foot pieces of pipe with the "T" fitting. Place the end caps on the other ends of the pipe pieces. Use pipe glue to hold the fittings in place.
Glue one male thread to the end of the 3-foot piece of pipe. Glue the elbow fitting to the other side. Glue the 4-inch pipe piece to the other side of the elbow. Glue the other male fitting to the top of the pipe. Wrap the male threads with electric tape. Allow the glue to dry for 24 hours.
Lay the pipes on the ground. Attach the elbow length of pipe to the "T" fitting so that the threaded end faces up. This is where you will launch the bottle. Fill the bottle about half full of water. Screw it loosely to the exposed threads, so that the water cannot escape. Attach the air pump to the valve. Pump water into the pipes until the bottle explodes off of the pipe and into the air. The rocket should be able to withstand several launches before it needs replacement. Replace the bottle when it crumples or holes form in the plastic.
Always take proper safety precautions when launching a water-bottle rocket. Wear safety goggles or glasses to protect your eyes. Onlookers should stand at least three feet away from the rocket during the launch to avoid being hit in the face.