I'm curious about some fluid dynamics stuff, and my first series of questions I have are to do with how air rises out of water... Having done some scuba diving, I know that divers use bladders to achieve neutral bouyancy and positive bouyancy so as to hover or rise through the water. Now for the questions: What sort of upward force is exerted by air under water? Take a cubic meter of air for the sake of ease. Is it the inverted equivalent of 1 cubic meter of water being tipped out of a bucket? ie: mass = 1kg, acceleration = 9.8m/s/s? (of course, the 'air resistance' would be very different to the 'water resistance') Or is it different because of the fact that the bubble is going 'up'? I do realise that the 'upward force' being exerted by the air in the divers bladder is a consequence of the water displacement, but can someone more accurately explain how that works? How does the displaced water 'push the air up?' instead of ...well...pushing down more.