Hi i want to know what the difference between general plane motion and rotation about fixed axis is? im using their formulas for work and energy study and as far as i see their general equations are the same. how do i identify which is which. also in a disk with planar motion, is the instantaneous centre ALWAYS where the disk touches the ground? please help!! i have a specific example which is confusing me but it is an example in my book i dont know how to bring it up online so you guys can help me?? any suggestions?