Try this experiment with your budding scientist. Gather one index card, scissors, a baking dish filled with water, and liquid dish soap. From the index card, cut out a curved triangle with a small, open, rectangular notch in the center of the back. Float your child’s boat gently in the baking dish filled with water. Ask him to pour a dollop of detergent into the notch and watch the boat take off across the baking dish. Why does it work? Explain to him that adding soap disrupts the surface tension, which then propels the boat.