Final answer:
The main forces acting on a ball swung in a circle are the centripetal force provided by the string tension, and gravity. Newton's third law explains the force as the ball exerts an outward force on the string, causing it to stretch, while the sensation of an outward 'centrifugal force' is due to the ball's inertia.
Step-by-step explanation:
When a student swings a ball attached to a string in a circular motion, several forces are at play. The primary force is the centripetal force, which acts on the ball towards the center of the circle. This force is necessary to maintain the circular motion of the ball and is provided by the tension in the string. According to Newton's third law, for every action there is an equal and opposite reaction. Therefore, as the string exerts an inward centripetal force on the ball, the ball exerts an outward force on the string, causing the string to stretch.
Another force acting on the ball is the force of gravity, pulling the ball downwards towards Earth's surface; however, this force does not influence the circular motion unless the plane of motion is tilted. Additionally, there is the force exerted by the person on the free end of the string to maintain tension, and air resistance which slightly opposes the motion, but these forces have been asked to be ignored in the given context.
It is important to note that in this scenario, the centrifugal force—often felt as an outward force—is not an actual force acting on the ball but rather a result of inertia. The sensation of being 'pulled' outward is due to the ball's tendency to continue in a straight line unless acted upon by an external force, i.e., the centripetal force provided by the string.