# What is the physics behind lifting a submerged bucket out of water?

When you submerge a cylindrical bucket into the water and let all the air out, trying to lift the bucket back out is particularly difficult if we keep it vertical to the surface. In order for the water to drain out, air must push into the cylinder through the edges, Why doesn't this happen?Also, at what height would the force (gravity) be so great that it would vaporise the water? (of course supposing a situation where air doesn't seep in through the sides)

The bernoulli equation should apply here, we can see that the pressure decreases below atmospheric as the bucket rises

• Bernoulli equation is for flowing fluid, not for approximately stationary fluid in a container, so it shouldn't apply here. – JMac Apr 7 '17 at 13:39
• The force is due to the weight of the water column you lift. – mikuszefski Apr 7 '17 at 13:40
• It works for a stationary fluid? I would imagine it's stationary – lucky-guess Apr 7 '17 at 13:49
• Moreover for all heights I expect an equilibrium process to start, creating vapor, see vapor pressure. Only that it should go faster for lower pressures i.e. higher columns. From that point of view there is no critical height. – mikuszefski Apr 7 '17 at 13:49
• oh, for some reason i began to think it was because of air pressure. The air pushes down on the bucket with extra pressure $pgh$ because the pressure of the water decrease due to an increase in height. The pressure at the bottom of the bucket at the surface is atmospheric because it must be the same at any depth for equilibrium. And the pressure decreases up the bucket due to decreasing weight of water above. But how does the water in the bucket 'know' to push with atmospheric pressure? – lucky-guess Apr 7 '17 at 13:58