Frictional force is the force that stops the ball.

Frictional force plays a crucial role in stopping the ball when it rolls on the ground. Let's understand why frictional force is the correct answer to this question.

Understanding the forces
When the boy kicks the football, the initial force applied to the ball is the muscular force. This force propels the ball forward and sets it in motion. However, as the ball rolls on the ground, it encounters various forces that act upon it.

1. Gravitational force:
Gravitational force is the force that pulls objects towards the Earth. It acts vertically downwards and is responsible for giving objects weight. Although gravitational force affects the ball, it does not directly stop the ball from rolling. Instead, it acts in conjunction with other forces.

2. Muscular force:
Muscular force is the force applied by the boy to kick the ball. This force initiates the ball's motion, but it doesn't stop the ball from rolling.

3. Mechanical force:
Mechanical force refers to the force exerted by machines or mechanical systems. In the context of the question, mechanical force is not the force that stops the ball. It might be involved in certain situations, such as if a machine or mechanism is used to stop the ball, but it is not the primary force in this scenario.

4. Frictional force:
Frictional force is the force that opposes the motion of an object. When the ball rolls on the ground, it experiences friction with the surface. This frictional force acts in the opposite direction to the ball's motion, gradually slowing it down until it eventually stops. Friction is caused by the interaction between the ball's surface and the ground.

Conclusion
In conclusion, the force that stops the ball from rolling on the ground is the frictional force. While other forces like muscular force, gravitational force, and mechanical force may be present, it is frictional force that acts in the opposite direction to the ball's motion and gradually brings it to a stop.