A cylinder rolls up an inclined plane, reaches some height, and then rolls down. The directions of frictional force acting on the cylinder while descending will be up the inclined. But what will be the direction of frictional force when the cylinder is ascending?? UP or DOWN Well, I think the answer must be down the inclined. But the book says it will be up. The reason given in the book is mgsinθ acts in downward direction in both cases. So the sense of angular acceleration should also be same in both cases. So friction always acts upwards Pls help if anyone understands the reason.