My son was wondering how sounds travel, how we hear them and such. Looking for a good way to demonstrate — visually — sound waves was a bit challenging in our small apartment. We tried his Djembe drum, which worked pretty well. We could feel the air coming out when the drum head was struck, but it was not quite enough to visualize. So we made an air cannon from an old tupperware container. The cylindrical container was used to hold 10lbs of flour before I managed to melt a hole into the bottom.
For the air cannon I cut off the bottom and put a 2″ hole in the center of the 9″ lid. Johann then helped me assemble it. We covered the bottom with a medium weight drop cloth plastic and used 100mph tape to seal it in place. Then we taped a few rubber bands to the drop cloth patch as the “trigger”. I knew it would be more effective if I could put the hole in the bottom due to the lid end being slightly wider than the bottom, but this was what we had to work with. Remember the melted hole in the bottom? Not centered and pretty good sized, larger than we wanted to start with.
The first shot was at Mom (of course). Johann laughed and jumped when he made her ponytail jump. We talked about how the canon worked, and he made the connection between the waves of air and sound waves. Then we spent the next two hours “shooting” the curtains, books, his paper dragon and of course each other. He tested the canon for distance (about 30′) and accuracy (about 4″ at 10′) before we took the canon to bath time to make waves. So many potential lessons all wrapped up in a $5 tub and 15 minutes of time — not to mention all the fun.
Next to build a receiver for our air cannon to demonstrate the tympanic membrane, and microphones.
