Consider rolling without a touch of M from P to slide to a point Q on the touch surface, spherical RADIUS R in the bath time t.In this image, the angle is negative (reduced)R
Consider rolling without slipping of M from point P to point Q on the surface of a sphere of radius R t the time in this corner it is negative (decrease) R.
Considering rolling without slipping of the M from point of contact P to contact points on the skin R sphere radius Q reservoir in time. T in this angle. so the value is negative. (decreased) R.