where A Alpha is a rotation about an unknown point r is a vector form centre of a point O to the centre of mass Mo = IgA + rxma Does this mean in plane motion the moment about some points is different? I always thought the moment is a free vector. So can you apply Mo any where and get the some rotation A? Mo = IoA which is true when o is fixed Mo = IoA = IgA + rxma is this correct? Also In my text there is a formula Mo = IoA + rxmao i don't really understand the last term though. In a physical sense what does it mean?