I think you're right! I made a diagram that helped me think through it visually: https://i.imgur.com/dospt2w.png https://i.imgur.com/dospt2w.png If circle A

I think you're right! I made a diagram that helped me think through it visually: https://i.imgur.com/dospt2w.png https://i.imgur.com/dospt2w.png If circle A is rolling around the edge of circle B from within, it is actually revolving around a new, smaller circle C which has the Radius Circle B - Circle A.