In the original Pirates of the Caribbean, Captain Jack Sparrow and Will Turner escape Port Royal by strolling out to an anchored ship. They do this by walking on the seafloor, using an upside-down rowboat to hold air so they can breathe. Imagine you have a block of steel and a block of styrofoam, both measuring 1 cubic foot in volume. We call this buoyancy, and for any object, the buoyancy force is equal to the weight of the water it displaces. The steel block displaces the same amount of water, so it has the same upward-pushing buoyancy force as the block of water.