You also asked about the source of the "power" - its actually the energy. This energy (the primer mover in the universe) comes from the warm water - it's thermal energy, or more specifically, it's the kinetic energy of motion of the water particles. As the thermal energy is absorbed by the dry ice, it sublimes (changes phase). The heat also causes the expansion of the CO2 gas (water's kinetic energy becomes potential energy of CO2 particles as they get farther apart). This causes an increase in the pressure of the somewhat constricted gas. As pressure builds, the force it generates increases. The thermal energy (internal to the water and carbon dioxide) becomes transformed into the mechanical energy of the carbon dioxide molecules. Your experiment is an exercise in energy transformations from internal kinetic energy of water to internal potential energy of CO2, to external kinetic energy of moving carbon dioxide, to external mechanical energy of the Hero's engine. Good luck, I've given you a lot to think about here. Most of the questions have been touched on. A little further research can help you produce a great science fair project if you're able to handle the mathematics. Two links that might help you are: 1. http://physics.kenyon.edu/EarlyApparatus… and 2.) http://cyclesantamonica.blogspot.com/200… The second one is not very accurate scientifically but it gives some ideas that may be helpful. Google "Thermal energy changes"
