Sinking and floating is a subject covered in many science classes, from kindergarten through college physics. Even the audiences of late-night talk shows get to predict whether an object will sink or float in water. And of course, we all know that witches will float if they weigh the same as a duck (Monty Python reference). Yet one of the most common examples of sinking and floating seems to go against common sense. How can something made of steel—a heavy metal—float in water?