$A$ wheel in uniform motion about an axis passing through its centre and perpendicular to its plane is considered to be in mechanical (translational plus rotational) equilibrium because no net external force or torque is required to sustain its motion. However,the particles that constitute the wheel do experience a centripetal acceleration directed towards the centre. How do you reconcile this fact with the wheel being in equilibrium?
How would you set a half wheel into uniform motion about an axis passing through the centre of mass of the wheel and perpendicular to its plane? Will you require external forces to sustain the motion?

(N/A) wheel is a rigid body. The particles of the wheel experience centripetal acceleration directed towards the centre. This acceleration is provided by internal elastic forces (tensions),which cancel out in pairs due to Newton's third law. Since the net external force and net external torque are zero,the wheel is in mechanical equilibrium.
In a half wheel,the distribution of mass about its centre of mass (through which the axis of rotation passes) is not symmetrical. Therefore,the direction of the angular momentum vector of the wheel does not coincide with the direction of its angular velocity vector. As the wheel rotates,the angular momentum vector changes direction,which requires a non-zero external torque. Hence,external forces and torques are required to sustain the motion of the half wheel.