1. . . . Surface Tension Air F F Liquid As a molecule moves through
the surface, we must “pull” to
oppose the attractive forces between
the emerging molecule and
surrounding solvent molecules.
As the surface of a liquid
is extended, more molecules
must come to the surface.
Note that the magnitude of the force will depend on
the depth or length(perpendicular to the figure. This
relates to the number of molecules involved. In
general, this is  = F/ l (dyn/cm).
Whether or not we are actually extended the surface of a liquid, the forces parallel to the
surface between molecules is present. This layer acts like a membrane in tension, similar
to a balloon containing air.

2. Wilhelmy Plate is one method to measure surface tension.
Balance
The balance will read
the weight of the plate
plus the surface tension
contribution.
Contact angle 
The contact angle indicates the
affinity of the liquid for the solid.
For θ less than 90o, the interaction
is favorable and the force pulls
down on the plate. For a contact
angle greater than 90o, the force
will be repulsive and will lower
the apparent weight. 
Liquid
Wbalance = Wplate +  p cos  p is the perimeter of the plate
 = Wbalance - Wplate
p cos 