Two steel thin-wall tubes in torsion of equal length are to be compared. The first is of

Question:

Two steel thin-wall tubes in torsion of equal length are to be compared. The first is of square cross section, side length b, and wall thickness t. The second is a round of diameter b and wall thickness t. The largest allowable shear stress is τall and is to be the same in both cases. How does the angle of twist per unit length compare in each case?