A bowling ball sits on a level floor of a subway car. If the car has a horizontal acceleartion a, what is the acceleration of the ball wrt the ground? Ball rolls w/o slipping. The forces that act on the ball are its weight, a normal force, and static friction. The weight and normal offset, so Friction = MA. But if we choose the point of contact with the ball as an axis, the net torque is zero?! So since torque is zero there is no angular acceleration and thus A=0? Something's wrong here.