Pure water and clean glass attract each other. If two flat circular plates of glass are separated by a film of water, both plates of glass will be attracted to the water and a force will be required to pull them apart. The water will curve in between the plates of glass at both ends because of surface tension forces and the pressure inside the water film will be lower than atmospheric pressure.
Since the films of water is concave in one direction and convex in the other the pressure difference is given by
where
is the surface tension of water.
The force
is then given by
Surprisingly large forces can be produced. If
and the thickness of water is
then with
we have
