The common mousetrap, when set, stores a finite amount of kinetic energy as the spring is pulled tight. When the hook is released, the "jaw" of the trap snaps shut forcefully; if you've ever had a mousetrap snap shut on your finger, you know that it is a considerable amount of force for such a small, light object. The mousetrap-powered boat harnesses this energy, but instead of releasing it in one snap, the energy is released gradually to move the boat forward.
Cut the balsa wood into a 10 inch by 5 inch rectangle. Cut one end into a point, making a boat shape. Cut a 4 inch by 2 1/2 inch notch into the other end.
Make four three inch by 1 1/2-inch rectangles out of the balsa wood for paddles. Cut the dowel down to six inches. Hot glue the paddles to the dowel, making sure they are centered and evenly spaced. Allow paddles to cool completely.
Wrap wire around the dowel on one side of the paddle and twist with a wire cutter. Trim to about 1/4 inch to make an axle pin.
Attach a one inch wire in a loop to one side of the back of the boat shape by hot-gluing one end to the top of the wood and the other to the bottom. Slide the end of the dowel through the loop and attach the second one inch wire to the other side, around the dowel.
Place the mousetrap on top of the boat shape on the same side as the axle pin. Hot glue the mousetrap in place.
Tie string to the axle pin and turn the dowel until you have about two feet of string wrapped around it. Tie the end of the string to the "jaw" of the mousetrap securely. Set the trap and tighten the string around the dowel.
Place boat onto the water and release the trap. The jaw should slowly begin to close, pulling the string and causing the paddle to turn, moving the boat forward.
Glue strips of balsa wood to the bottom of the boat to help balance it, if necessary. Try using different materials such as foam and different shapes.