Friction plays a crucial role in the rotational dynamics of a hollow cylinder rolling down an inclined plane. It generates a torque that influences the cylinder's rotational acceleration, thereby affecting its angular velocity. When the cylinder rolls without slipping, friction ensures that the rotational inertia is effectively utilized in the motion. The interaction between friction and rotational inertia is essential for understanding the overall motion of the cylinder. Thus, friction significantly impacts both the rotational inertia and angular velocity of the hollow cylinder.