You have a jar filled with water and a glass. If you pour some water into the glass and place a cork in it, the cork will float towards the edges of the glass. What is the easiest way to make the cork float towards the center?
Since the liquid molecules adhere to the glass molecules on the sides of the glass, the water level there is higher and buoyancy makes the cork float in that direction. If you fill the glass all the way to the edge, then the water surface will be convex and the cork will float towards the center.