Conservation of momentum applies only to collisions. Momentum is the same as force. Moving masses in the absence of gravity do not have momentum. The center of mass of an object must be inside the object. Center of mass is always the same as the center of gravity.
Centrifugal forces are real.
An object moving in circle with constant speed has no acceleration. An object moving in a circle will continue in circular motion when released. An object is circular motion will fly out radially when released. Any force acting on an object will produce a torque. Objects moving in a straight line can not have angular momentum.