My textbook says the following: "If the center of mass of the system is not accelerating relative to an inertial frame, that origin can be any point. However, if the center of mass of the system is accelerating, the origin can be only at that center of mass. As an example, consider a wheel as the system of particles. If the wheel is rotating about an axis that is fixed relative to the ground, then the origin for applying Eq. 11-29 can be any point that is stationary relative to the ground. However, if the wheel is rotating about an axis that is accelerating (such as when the wheel rolls down a ramp), then the origin can be only at the wheel’s center of mass." Can someone explain to me why we must calculate torque and angular momentum with respect to the center of mass if the center of mass is accelerating?