The Earth makes heat deep below the ground all the time. That heat turns water into steam. In this model, steam from a pot shoots through a small hole in foil and spins a pinwheel. Fewer holes make a stronger jet and a faster spin.

Deep underground, heat and pressure turn water into steam that rushes upward through wells, spinning large turbines to generate electricity. You can model this same process at home. Seal the top of a cooking pot with aluminum foil, poke a small hole in the center, and set the water boiling. When steam shoots through the hole, hold a pinwheel over the jet and watch it spin.

When water boils in a sealed pot, steam shoots through a small hole in the aluminum foil on top. Hold a pinwheel over that jet and it spins — the same basic idea behind a geothermal power plant turning underground steam into electricity. Fewer holes mean a stronger jet and a faster spin.

When water boils in a sealed pot, steam builds up and pushes hard against the foil lid. You poke a small hole in the center, and that force has only one way out — a focused jet that spins a pinwheel. Fewer holes mean a stronger, faster jet.