This interactive brainteaser from the NOVA: "Voyage of Doom" Web site challenges you to figure out what happens to the water level when a rock is resting in a boat and when it is submerged in water.

Each student uses a small quantity of modeling clay to make a boat that will float in a tub of water. The object is to build a boat that will hold as much weight as possible without sinking. In the process of designing and testing their...