Re: Tenkan and Centrifugal Force
I think Rob is on the right path here. To me in Japanese kaiten generally has the meaning to rotate or go around. It's most often used in a "mechanical" or more tangible sense like kaiten doa (rotating door) or something like that. However, tenkan on the other hand has an additional connotation of change due to use of the "kan" character meaning change. It can also be used in more intangible situations. Such as a turning point in time or a changing turn in feelings. Because of this additional connotation of change I think this is why the term tai no henko (change of body) is used by people who practice Iwama style aikido to substitue which is called tai no tenkan or simply tenkan by the majority of aikido people.
I guess the major difficulty comes because like others I've heard the terms tenkan and kaiten used interchangeably to describe the same movements. For instance what Rob described as kaiten above I've heard to referred to as tenkan as well, sometimes han-tenkan (half-tenkan). I don't know if there is a right or wrong usage.