In a vertical circle, the tension in the rope is at its maximum when the ball is at the bottom of the circle due to the combined effects of gravitational force and centripetal acceleration. At this point, the tension must counteract the weight of the ball while providing the necessary centripetal force to maintain circular motion. The forces acting on the ball include gravity pulling down and tension pulling up. When the ball is at the top of the circle, the tension is at its minimum because gravity and tension both act in the same direction. Understanding these forces is crucial for explaining the dynamics of the ball's motion in a vertical circle.