The secret inside the barrel
Partway through the build, Adam wondered how the launcher would work, and he said the mystery was part of the fun. But here’s the answer he was looking for.
The foam cannonball sits in a small launch piece inside the barrel. A rubber band connects each side of the launch piece to the barrel, and a loop of string tied to the launch piece hangs out the back. When you pull the string, the launch piece slides back and stretches the rubber bands. When you let go, the rubber bands pull the launch piece forward fast, and it pushes the cannonball out of the barrel.
A stretched rubber band stores energy, called elastic potential energy. Once it’s released, that energy turns into kinetic energy, the energy of motion, and the launch piece passes much of it to the cannonball. A longer pull stores more energy and sends the cannonball farther.
Adam found the trick to a clean launch: pull the string straight back. A straight pull stretches both rubber bands the same amount, so they pull the launch piece forward evenly. The launch piece moves straight down the barrel, and the cannonball goes where you aim it.
Aim high, aim low
Adam called the sliding dowel “brilliant.” The cannon tilts up and down on its pegs, and the dowel props the barrel at whatever angle you choose. That means kids can run their own experiment.
Try a launch angle challenge
Set the cannon at a low angle and fire three cannonballs. Mark where each one lands with a strip of tape.
Raise the barrel a little and fire three more, using the same length of pull.
Try a high angle, then compare your tape marks.
Ask your kid which angle sent the cannonballs farthest and why they think it worked.
Keeping the pull the same each time makes it a fair test, since the angle becomes the only thing that changes. Scientists call that controlling a variable.
Ready, aim, launch
Adam summed up his build with a compliment we’re still smiling about: “KiwiCo, your engineering continues to surprise and delight me personally.” Kids get to make the same discoveries he did, from the launch piece hidden in the barrel to the dowel that sets the angle, and then put them to the test. Start with one launch and one strip of tape, and let your kid take the experiment from there.
The Cannonball Launcher is made for ages 5 and up, and it’s a great holiday gift. Share your launch photos and videos on Instagram with @kiwico_inc, and tell us in the comments how far your cannonballs flew.
