Force between two plates

If two flat plates are placed in contact with a thin film of water between them it is found difficult to pull the two apart. This is due to the reduced pressure within the water film, since the edges will be hemispherical (Figure 1).


Since the film is convex in one direction and concave in the other the pressure difference (Dp) is given by:
Dp = T(1/r — 1/R)
and the force (F) required to separate two plates of area A is given by: