We all know that moon is under the influence of Earth gravitational force and vice versa. This force causes the circular motion of Moon (and Earth as well). Earth pulls Moon with a force F and Moon pulls Earth with the same force. This has occupied me a long time: Will Moon eventually fall down to Earth (collision is maybe a better term)? If not, how should I try to understand gravitation? At the moment I use this kind of example: Earth is like me swinging an object around me, the object is attached to a string and the string is like gravitation, it holds the object on orbit. Still, this causes some problems to me. When I swing that object I'll lose energy (or do I?) - I can't swing it forever. However, Earth doesn't loose any energy "swinging" the Moon, does it? What is wrong in my model?