"elephant toothpaste experiment" cannon?

ForumFire

I saw a video of an experiment called "elephant toothpaste" on youtube, where a guy put hydrogen peroxide and potassium iodine in a graduated cylinder, and it all foamed up, and went out of the graduated cylinder. If you put the chemicals in a pipe with a cap on one end, and a valve on the other, would it shoot it like a cannon? or perhaps it would be powerful enough to be like a jet pack, and you could fly around your neighborhood?

mgb_phys

Unfortunately not.
There is something called conservation of momentum.
That means that the speed*mass that you move up must equal the speed*mass of the thing that goes down.
The foam doesn't weigh very much so to lift you 70kg at 1m/s (walking speed) you would have to spit out 70kg of foam at 1m/s or 7kg of foam at 70m/s. Since foam is very light you would need very high speed.
You can see this with rockets, because the mass of the exhaust gas is so small you have to fire it out at very high speed - while with a firehouse sending out heavy water you feel a force at much lower speeds.