1. The problem statement, all variables and given/known data Suppose a disk of radius 'r' is rotation on a surface. If the center G moves a distance 'd', then what is the distance traveled by a point on the top of the disk (on its edge or circumference). 2. Relevant equations theta = s / r ; where theta is the rotation in rad, s is the arc length, r is the radius 3. The attempt at a solution I know that if G moves a distance 'd', then the entire circle rotates 'theta'=d/r. But I'm not sure how to make this a general case. A thought: Can i treat the point of contact between the disk and ground as a n "origin" and then state that a point directly above it on the edge of the disk moves '2r*theta' ? Thank you, Alex. ------- EDIT: I hope you don't mind if I make the problem a bit more specific. Suppose a gear of radius r_o is moving with an inner hub of radius r_i. If I know the origin moves 'd', then how far does a point on the circumference of the inner hub move?