Problem 1.305

Determine the relationship between the torque \(N\) and the torsion angle \(\varphi\) for (a) the tube whose wall thickness \(\Delta r\) is considerably less than the tube radius; (b) for the solid rod of circular cross-section. Their length \(l, \mathrm{ra}-\) dius \(r,\) and shear modulus \(G\) are supposed to be known.