I like spud gun projects which use pvc and such like but the truth is most people don't have pvc and valves laying around their home.
This project uses an inner tube as found on a push cycle. I have literally tens of these around which have suffered punctures and because the cost (I pay less than 50pence each) it doesn't make sense to try repair them.
This is my first project using a inner tube and I'm sure it could be modified to produce much better results and be easier to use.
The end result is a air pressure powered gun which can launch projectiles. You could modify the projectile into a rocket or something cool like that if you don't like guns :)
So all you need is:
An inner tube from a push cycle
A standard pump used for inflating your push cycle tires
A projectile such as an old 35mm film canister
Hot glue gun OR elastic band
For your safety I must insist that you wear some kind of armor when carrying out this instructable. In the video I was wearing a kevlar skin color shirt inc ase the rubber inner tube was to explode and the sharp shards of thin rubber sliced through my torso. Also I must insist you wear some kind of eye protection again in case those shards get you. In the video I'm wearing low profile security specs which are hard to make out but please ensure you wear them :)