We know that in a fluid the molecules are continuously bumping into the object (here a cylinder) placed in it. But why does it happen so that the molecules at the bottom are applying more force than that from the up? That is to say what is the molecular picture of fluid pressure at different depth?
From your other question: "The water above applies pressure according to it's depth, the water below always has greater depth, so applies greater pressure. If the cylinder's weight is less than the difference in the upper and lower pressures, then it will be pushed upwards. In other words if the cylinder weighs less than the same volume of water, it's displacement, it will float up out of the water, until the portion of it below the water level displaces it's weight."------- As for an object on the bottom, for it to loose bottom water pressure, it would have to fit with so tight and precise a fit that water molecules could not get between the object and the bottom, like a suction cup.