I remember making thee Coke can cannons for tennis balls. Back when we had "pop tops", you could completely remove top and bottom of the top can, remove the top of second can and then open bottom of second can with punch can opener with about five holes, put about five holes in the top of bottom can with the punch can opener and put a small hole in the middle of it. Tape them all together and squirt a little Ronsonol lighter fluid in it, swing it around a couple times to get the fuel/air mixture right, set it on the ground, drop a tennis ball in it and light the hole in the bottom can.
If you did it right a tennis ball would shoot up about 100 feet. If not, remove tennis ball and try again. My dad always wondered where all his lighter fluid went - he should of known, he was the one who showed us how to do it.
With the invention of the stay in place opening top and necking down the size of the cans this fun activity was ended.
