FLAMMABLE WHEN WET
Use electricity to split tap water into
hydrogen and oxygen gases, then use
this explosive gas mixture to power a
two-stage, electronically timed rocket.
Air-powered water rockets are easy to build and the fuel is
free, but do you want to push the envelope? How about a
two-stage water rocket? And instead of pressurized air, how
about an explosive gas? I know the perfect gas to use.
Back in high school chemistry, I learned about the electrolysis of water, using electricity to break water molecules into
hydrogen and oxygen gases. A spark recombines the elements
back into water, releasing energy that vaporizes the water. The
hot water vapor causes a rise in pressure, and in this project
we use this pressure to push water out of the soda bottles
and propel the rocket upward.
This rocket is controlled by an onboard timer circuit that
runs off a 9-volt battery and ignites the gases electrically
using model rocket igniters. The circuit’s variable resistor lets
you precisely time the interval between first- and second-stage ignitions to attain maximum height. LED firing signals
provide a visual countdown, and when the gases ignite they
produce a delightful explosion.
Photograph by Sam Murphy
Set up: p. 93
Make it: p. 94
Use it: p. 99
Tom Zimmerman is a member of the User Sciences & Experiences Research laboratory at IBM’s Almaden
Research Center. He graduated from MIT. He was profiled in MAKE, Volume 04.