A tennis ball launcher propels a tennis ball using some form of propellent--be it a spring or compressed air from an explosive force. Build a homemade tennis ball launcher from a few common household items, along with some supplies from a hardware store. The tennis ball launcher does not require any dangerous materials to "fire" the tennis ball, and it can be used over and over again.
Place a sheet of newspaper on a table to protect the surface. Stand the PVC pipe on the newspaper. Measure 2 inches down from the top and make a mark. Drill a hole through the sides of the PVC pipe at the 2-inch mark with the portable drill.
Measure 8 inches down from the 2-inch mark and make another mark. Drill a hole through the sides of the PVC pipe at the 8-inch mark.
Apply bonding glue around the rim of the open end at the top of the PVC pipe. Place the PVC cap on the opening. Let the bonding glue set for an hour.
Turn the PVC pipe over on the newspaper. Drop the spring into the open end of the PVC pipe. Push the spring all the way down to the other end of the PVC pipe with the end of a wooden dowel.
Insert one of the two metal nails, point first, into the hole closest to the PVC pipe's cap. Push the nail through the spring inside of the PVC pipe and out the other side. Apply bonding glue to both holes the metal nail is in. Let the bonding glue set for an hour.
Drop a tennis ball into the open end of the PVC pipe. Ram the tennis ball down to the other end of the PVC pipe with an end of the wooden dowel. Hold the wooden dowel in place while pushing the other nail through the holes in the PVC pipe that are still open.
Go outside and aim the tennis ball launcher at a target that is unlikely to cause the ball to ricochet back at you--for example, a bush. Pull the nail out of the hole to fire the tennis ball at the target.
The launched tennis ball can cause injury or damage to property if the launcher is aimed at a person, and animal or something breakable.