1. The problem statement, all variables and given/known data 2. Relevant equations Angular momentum 3. The attempt at a solution So I have my work shown in the two pictures. rm, rf denote the position vectors to the center of mass and point of application of force respectively (with respect to the chosen origin of course). Is this the way to do it? I've seen a way done by some others where they take the origin of the coordinate system to be instantaneously co - moving with the point on the ball that is in contact with the ground (so that again torque will vanish with respect to this origin because it acts at the origin itself) and use the exact same terms for the final and initial angular momentum. This frame will however be accelerating with respect to a fixed coordinate system due to friction but is angular momentum unaffected by this?