It's just an imaginary experiment to show analogy between planet movement and the movement of the stone turning in a slingshot ...

Something like the one you see on Fu1.jpg.
When I click on the hand, the stone is free to go away (see Fu2.jpg) but when I click on the earth, the motion of the moon stops and the moon fall on the earth (see Fu3.jpg) ... I'd like it to be thrown away ... like if they were no earth at all ...

Is it more clear now ?