This is a solved example in my text book"Engineering mechanics dynamics. R.C.Hibbeler" :
The 3 kg disk is attached to the end of a cord. The other end of the cord is attached to a ball and socket joint located at the center of the platform. If the platform rotates rapidly, and the disk is placed on it and released from rest, determine the time it takes for the disk to reach a spead great enough to break the cord. The maximum tension the cord can sustain is 100 N.. And the coefficient of the kinetic friction between the disk and the platform is 0.1
when the free body diagram of the particle was drawn, the friction force was considered in the tangential direction,, but it wasn't considered in the normal direction(tension was only considered) why? I was expecting that there is kinetic friction in the normal direction, since the disk is moving relative to the platform.