* Equilibrium means no net force. For an object to be in equilibrium, all the forces acting on it must cancel out, resulting in a net force of zero.
* Rolling involves friction. Even though the ball is moving at a constant speed, there is friction between the ball and the surface it's rolling on. This friction acts as a force opposing the motion.
* To maintain constant speed, a force is needed. Since friction is acting on the ball, a force in the direction of motion is required to counteract the friction and keep the ball moving at a constant speed. This force could be coming from an initial push or from a constant, external force.
In summary:
While the ball's velocity is constant, it is not in equilibrium because there is friction acting on it, requiring a counteracting force to maintain the constant speed.
