Lets say we have a ball on a string and we spin it around. The ball will undergo circular motion. The tension in the string is what provides the centripetal force, directed inwards. Then what would be the force directed outwards? (According to Newton's third law of motion). It cant be centrifugal, because that is not a real force. Or lets say if we were to draw a free body diagram of the ball, what forces would be present? Assuming there is no tangential acceleration and that the ball is travelling at a constant speed.