A mug holds litres of washing-up foam whose bubbles are about mm across
PHYSICS · Multi-part · Fermi University Physics · Fluids & Continuum Physics · Fluid statics and the continuum picture · Fluid statics and the continuum picture
Fluids and Continuum Physics, Ch Surface tension, capillarity and wetting
Problem
A mug holds V=0.40 litres of washing-up foam whose bubbles are about 1.0 mm across. Estimate the surface energy stored in the foam. Model the foam as N spherical bubbles of diameter 1.0 mm that fill the volume V; each bubble is bounded by a soap film with two liquid faces, and every film is shared between two neighbouring bubbles, so each film must be counted once. The soap solution has γ=0.025 N m−1 (equally, 0.025 J m−2 per face), and the liquid in the films is so thin that its own volume may be ignored.
((a)) Estimate the total area of film in the foam (each film counted once).
((b)) Estimate the surface energy of the foam.