1. The problem statement, all variables and given/known data source:http://www.wired.com/2014/07/a-rolling-object-accelerating-down-an-incline/ For a ball rolling on an incline, I know how to calculate the acceleration. However, I am quite confused about a situation. What if static friction acting on the ball is equal to the component of gravity along the plane, which means, net force acting on the ball is zero. But net torque of the ball is not zero, which means the ball is supposed to rotate. Under this situation, either the ball rolling down or not is quite confusing. Considering net force, it should not have translation. but considering net torque, it should rotate, and then roll down. What will happen ? Is there any mistake on my analysis ? Please help! Thanks a lot!