Static friction provides the net inward force until slipping begins; then kinetic friction acts.
This interactive 3D physics simulation demonstrates how friction allows a disk to move in circular motion on a rotating turntable. The simulation shows the difference between static friction and kinetic friction, and it avoids treating “centripetal force” as a separate new force.
While the disk sticks to the turntable, static friction supplies the force needed for the disk’s circular motion. Because the turntable has angular acceleration, static friction may have both an inward component and a tangential component.
Slipping begins when the required static friction becomes larger than the maximum available static friction. At that moment, the disk no longer co-rotates with the turntable. The contact force changes from static friction to kinetic friction.
Before slipping, the friction force is whatever value is needed to maintain circular motion, up to its maximum value. After slipping begins, friction does not become zero; it becomes kinetic friction and acts opposite the relative motion between the disk and the turntable surface.
Static friction adjusts its magnitude and direction to keep the disk moving with the turntable.
After slipping begins, kinetic friction acts opposite the disk’s motion relative to the table.
The inward component of friction provides the inward acceleration needed for circular motion.
The graph compares the actual friction force with the maximum static friction and kinetic friction.