Submarine

When a body is placed in a liquid, a buoyant force proportional to the volume of the immersed part of the body acts on it. If the buoyant force exceeds the force of gravity, the body will float on the surface. When the bottle is filled with water, its volume remains unchanged, but its mass increases. At a certain moment, the force of gravity exceeds the buoyant force, acting on the submarine and causing it to sink.