Physics projects come in all shapes and sizes. They help reinforce learning by putting book knowledge to practical use. The tennis ball launcher is a popular project and can be used in a variety of ways. The design below uses chemical propellant and fire to launch the ball. If your instructor has forbidden the use of these items, you should consider using a spring, slingshot or catapult design. However, if propellant is not on your restricted list or you want to improve your understanding of projectiles or if you just want to do something fun on a summer afternoon, follow the directions below to create your own tennis ball launcher.
Cut the bottom and the top off six of your cans, so each looks like a tube. Clean them well by washing in soapy water. Allow the cans to air-dry. Sniff the cans. If you can still smell the former contents, wash them again.
Punch six triangular holes around the top of your last can. Do not remove either the top or the bottom. Shake the can hard to remove the contents, or pry food out with tweezers. Once the can is empty, wash it well. Rinse the can and allow it to air-dry.
Using a hammer, place a nail ¼ inch from the bottom of the can with triangles punched around the top, creating a hole. Be careful not to nail all the way through the can.
Connect the tube cans end to end, securing them with tape. Then attach the can with the holes, inserting the punched holes into the last tube can, but leaving the nail hole exposed.
Once you have secured each junction, wrap the entire thing in tape. Begin just above the nail hole and wrap toward the top. Repeat as many times as you'd like. When in use, the launcher gets hot, and extra layers of tape may help it last longer.
To use your tennis ball launcher, hold the barrel upright and place the tip of the lighter fluid canister into the nail hole. Squirt a small amount of fuel into the can. Turn the launcher upside down and swing it five or six times to distribute the fuel through the barrel of the launcher. Place a tennis ball in the open end of the launcher, pushing it down to the bottom of the first can. Aim the barrel at something safe, like the sky. Use your mouth and blow into the nail hole to vaporise the fuel. Light a match and hold near the nail hole. If everything went right, you will hear a muffled bang and the tennis ball will shoot into the air.
Asparagus cans generally have the correct diameter for the barrel. Do not use too much fuel. Approximately ½ oz per use is adequate. Make sure your cans are straight and the tape is tight. If the tennis ball is too large, cut a small hole in it so it can be squeezed into the can, but be sure to note this modification, as it may affect flight time and distance.
Always use care when handling combustible liquids. Any explosion, even a small one, can be dangerous. Wear protective goggles and gloves when igniting the fuel. If you are under 18, use under the supervision of an adult.