Another idea for a science experiment

I was watching MythBusters tonight on Discovery and had a great idea, well, I should say saw a great idea for a science experiment for when Sydney is in school. Evidently there is this myth about some tribe that build a cannon overnight out of a tree and a block of granite. They ground the granite into a circular cannon ball and drilled a hole into the tree trunk to create the cannon barrel.

Now it might not be acceptable to actually fire a cannonball, but building a cannon out of a tree trunk would be a pretty fun project to do when Sydney gets older. Marked for reference.