You have a weight on one end of a piece of string and you run that piece of string through a tube, and then on the other end you attach a cork. You hold on to the tube and try and keep the cork spinning at a constant radius, such that the weight stays dangling at the same height. As you increase the radius of the circle, the time to complete a revolution takes longer. Why does the angular speed decrease when the radius is increased? I guess it's sort of the same question as, if Mercury were the same size as Earth, would it's speed during revolution still be faster than Earth's? And if so, why?