Question
If an elastic film can be modelled as a square grid formed by a very small spring each of stiffness k.show that potential energy U OF THE FILM if stretched uinformally and isotropically in all directions is given by U=K(√S-√So)^2.here So is the area of unstreched film and S is area of stretched film.Now such an elastic film is used to fabricate a spherical ballon of radius ro in relaxed state.Find the dependence of air pressure p inside the ballon on its radius r.Assume vacuum outside the ballon.