“This was built as an experiment to amuse secondary school pupils at “Make It In Scotland”, a careers event organised by Careers Scotland, which took place in Motherwell in February and March 2003. It uses a vacuum cleaner to suck a projectile up a long pipe. The intension is that the missile should then carry on out the end rather than being brought to a dead stop by the suction. To get the best results, both ends are blocked off with card, then the card at the back of the tube is removed quickly. The vacuum keeps the second card in place until it is knocked off by the projectile.” Link. Also see the $5 Bazooka.
The Vacuum Bazooka