The specific gravity of fish is so nearly equal to that of water, that they can move about anywhere beneath its surface.
How do fish rise and sink in the water?
Fish rise and sink in the water by means of an air-bladder in their bodies.
How does the air-bladder help the fish to rise or sink?
When the bladder is filled with air, the specific gravity of the fish becomes lighter, and it rises towards the surface; and when the air is forced out, the specific gravity becomes heavier, and the fish sinks towards the bottom.
Why does cream rise to the surface of milk?
Because the specific gravity of the cream is less than that of the milk.
Why does oil float on water?
Because the specific gravity of the oil is less than that of the water.
Why can a fat person float more easily in the water than a lean person?