SURFACE TENSION is defined as the force acting per unit length perpendicular to the line drawn on the surface of liquid. The tension arises due to the attraction of the particle in a bulk in the surface layer of the liquid which minimizes the surface area. For the given volume of a liquid, the surface area of the sphere is minimum and the drop of liquid-like mercury or rain droplets are spherical. The inner force on the molecules of the surface minimizes the surface area and forms a drop.