it's very easy to make and with luck you can launch it about 200 feet.
all you need is a plastic 16 oz. bottle with a cheap lid. (crystal geyser works great)
and baking soda and vinegar.
this is my first instructable so don't judge it too hard
Step 1: mix!!
put in baking soda and vinegar, about 2 tablespoons of each, and shake until the bottle is good and hard.
you can experiment and put different amounts of the stuff but make sure it doesn't blow up!
i'm not liable for anything bad that happens during your experimenting, broken windows, broken bones, loss of limbs, ect.