Why the surface of water column is concave?

Answer 1

The shape of the surface of a column of water actually depends on what the sides of the container are made of, but for a glass tube the surface is concave. This is because water likes to wet the glass. Some materials, such as Teflon, water does not like to wet. On a teflon surface, water will form little beads and does not like to stick. A water column in a teflon tube would have a convex surface.

This is because the wet glass has less surface energy than the dry glass. Since the universe always likes to reduce the total energy of a system, the water rises up the sides to make more wet surface and reduce the total energy. With a teflon surface, the dry surface has less energy and so the water is "repelled" from the surface.

Answer 2

The surface of a water column is concave due to the cohesive forces between water molecules. These forces cause water to "stick" together, forming a thin film on the surface that pulls inward, creating a concave shape. Gravity also plays a role in shaping the surface, with the weight of water pulling it down towards the center.