This question already has an answer here:
This ball oscillates at the bottom of the spherical bowl which has sufficient friction that it doesn't slip throughout the motion and rolls without slipping. At the extreme points of its motion (as seen in the image) both its velocity and angular velocity is zero.Its translational kinetic energy has been converted into gravitational potential energy. My question is that where does the rotational kinetic energy go? As the gravitational force passes through the center of mass it doesn't exert any torque, and the friction does not do any work as the ball rolls without slipping implying its lowest point in contact with the bowl is stationary.There is no other torque on the ball and hence the rotational kinetic energy should be constant. But the fact that friction does not perform any work against the rotational energy implies that its rotational kinetic energy shouldn't change throughout the motion. But that cant be true as its velocity changes and for the ball not to slip its angular velocity should change. Where in my argument am I going wrong? *I think that the answer could be that the normal reaction doesn't pass through the center of mass and it exerts a torque.