|MadSci Network: General Biology|
John, I cannot think of any reason why a person who starts off floating should sink later. It is like asking 'How long can a ship float in water ?' The buoyancy of a human - or a ship - would only change if there was some change in the density of the floating object. If the density of the human is less than that of water (0ne gramme per cubic centimetre) then they will continue to float so long as they are alive. Even if the person drank a lot of water, this should not affect their buoyancy, as the water consumed would be of the same density as the water they were floating in. If, however, as tends to happen to people floating in rough water for a long time, they were to inhale more and more water, then that inhaled water would fill up the air space in their lungs and make them more likely to sink. Apart from the air space in our lungs, the other factor which helps us to float is the amount of fat in our bodies. Women have, on average, a higher proportion of fat in their bodies so that a drowning woman would probably float for longer than a drowning man. To that happy thought I can only add that the behaviour of bodies after they have stopped breathing is much more interesting - but you did specify that they had to be alive ! Hope this helps your research. Will
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