Some people think that some objects just float or sink because of how much it weighs. But it really depends on its density: the weight and size. For instance, take a metal block and a styrofoam block that are the same size. You probably think that they both weigh the same, but the metal block weighs more because it's denser than the styrofoam block. If you took the metal block and spread it thin it would float. If you took the styrofoam block and crushed it into a small round ball it would sink. When you spread out the metal it became less dense than the water and the styrofoam became denser than the water. Density is determined by the size and weight.