Canon

Cannons made from soda cans. Based on my knowledge, a cannon consits of a barrel, pressure chamber, and a projectile. Within the chamber an ignition occurs creating an explosion, propelling the projectile through the barrel.

Basically like this.
  

However, there is more physics involved. The forward momentum of the explosion must be equally counterbalanced by something. Therefore the base of the cannon must be large and stable enough to withstand the opposite force. We plan to make "BOOMS" in our classroom in the near future, with our class-made cannons made of cans. Good luck to us.