Buoyancy: An object’s ability to float in water or other fluid.
Density: How much something weighs as compared to how big it is—or, an object’s mass per unit volume. Something big and light, like a balloon, has low density. Something small and heavy, like a rock, has high density.
Displacement: The moving of something from one place to another. For example, when an object is placed in water, it pushes some water out of the way and takes its place.