Problem 4.80

A disc \(A\) of radius \(R\) suspended by an elastic thread between two stationary planes (Fig. 4.24 ) performs torsional oscillations about its axis \(O O^{\prime} .\) The moment of inertia of the disc relative to that axis is equal to \(I,\) the clearance between the disc and each of the planes is equal to \(h,\) with \(h \ll R .\) Find the viscosity of the gas surrounding the disc \(A\) if the oscillation period of the disc equals \(T\) and the logarithmic damping decrement, \(\lambda\).