I have posted this question before but have not got a complete answer. I have since been thinking about it quite often, yet still have not had a conclusive answer. I'd really appreciate if someone can give a full explanation, since it is a fact known by most. 1. Under all ordinary conditions, would a ball released from rest start rolling down a frictionless inclined plane with just the force of gravity pulling it down? Or is it really just going to slide down? 2. Now let's suppose a gigantic ball released on the slope of an enormous frictionless inclined plane, so that the gravitational force varies considerably from the bottom to the top of the ball? What would happen? Would the ball then start rolling?