Suppose that a drop of water is placed between two glass plates, which are then pressed together to create a film of thickness 2h and radius R, as shown in Fig. P4.10. You may assume that the contact angle for water on the glass is nearly zero.

(a) Derive a general expression for P within the water film, which you may then simplify by assuming that h ≪ R. (Although the air–water interface is concave outward in the horizontal view that is shown, when viewed vertically it is convex outward.)

(b) How large a load (mass of lower plate plus anything attached to it) could be supported if h = 5 μm and R = 1 cm?

Transcribed Image Text:

Air P= Po Glass Water Glass 2h ļ R Air P= Po Figure P4.10 Capillary adhesion due to a thin film of water between glass plates.