Question

What do you understand by the term surface tension?

Answer 1

Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas, acts like a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air). If the surface is between two liquids (such as water and oil), it is called "interface tension."

Answer 2

Surface tension is the force with which the molecules of a liquid below the surface attract or pull the molecules at the surface. For molecules inside the liquid this net force is 0 as forces from all sides neutralize. FOr molecules on surface, there are no liquid molecules on top. The attraction between gas/air and liquid molecules is much less than that between liquid molecules. This is the cohesive force among liquid molecules which is more than adhesive forces between gas and liquid molecules.
Due to this surface tension, the shape of the drops tends to become spherical as the surface area tends to become minimum.
Due to surface tension, the surface of a liquid in a small capillary tube (thin tube) tends to curve at the edges and flat at the centre.