Hi all, I have a question about how to analyze the problem of a ball rolling down an incline plane. Assuming there is friction, at each instant the ball swivels about a pivot point on the incline that is stationary due to static friction. We then would analyze the torques about this point and find the rate of change of angular momentum. However, at every instant, aren't we switching to a pivot point at a different location along the incline. Angular momentum is dependent on the choice of the coordinate origin and so is torque. Am I understanding the way we are analyzing this problem correctly? or am I over complicating things? So if we are analyzing the system each instant and at a different pivot point, and a different coordinate origin, how can we piece together all the information so the speak and describe how the ball is moving to a single stationary observer?