So I understand how surface tension arises: The molecules in the bulk of the liquid face forces from all directions, and their resultant is zero. The molecules on the surface, on the other hand, have a net component of force in the downward direction, since there are no molecules above them to provide an upward force and cancel this component. This means the surface molecules have higher energy than those in the bulk.
How does this explain the "sheet like" tendency of the surface? If the surface were to behave like a stretched sheet,then there should be a "pulling force" in two directions along the horizontal along the surface.
How do you determine the direction of force due to surface tension? In my textbook, it states the direction is perpendicular to an imaginary line dawn along the surface. How do you explain that a needle kept on the surface doesn't sink? The force of surface tension must act upwards. How/why? How would we determine the force acting on say, a sphere kept on the surface? Is there any connection with direction of force with the fact that surface molecules have a net downward component?
Lastly, how do you explain the tendency to reduce surface area with the explanation I presented regarding the origin of surface tension?
