Question Checkup 30.3.2: The torque given by Eq. (30.17) is zero at θ = 0° and at θ =......

From \theta = 0°, a small displacement results in a configuration with a torque that would return \mu toward \theta = 0°, and so \theta = 0° is a stable equilibrium (apply the right-hand rule to Fig. 30.14). However, near \theta = 180°, a small displacement results in a torque that would also push \mu toward \theta = 0°; thus \theta = 180° is a condition of unstable equilibrium.