A cylinder is rotating about its axis and is placed on an inclined surface without linear velocity, the coefficient of kinetic friction between the surface and the cylinder is μk . During Δt1 it stays at the same height till the rotation stops. From that moment it takes Δt2 for the cylinder to reach the bottom of the inclined surface. What is the angle of inclination of the surface?
My question is why does at time Δt1 there is a kinetic friction but not static- because as the problem states cylinder doesn't move?