You make a polish cannon like this:
Get three soda cans. Two of them you cut off the tops and bottoms so you have a pair of cylinders. The third one, you poke a small hole on the side, about 1/4" above the bottom of the can.
Get duct tape and connect all three cans together, with the can that has the small hole as being the "bottom".
Get a tennis ball and stuff it down the top. You may need a little oil to lube the insides of the can.
Put a little lighter fluid into the bottom can through the small hole, and shake it up a little.
Aim the cannon assembly like a mortar. High angle, low angle.... don't matter.
Put a match to the hole and watch the tennis ball go shooting out.