First of all, I did not major in Physics, but I did pass GCE with A. (This is to make a point, not to boast.) But there's a matter that doesn't make any sense to me, and none of my acquaintances could give me the clarification so I came to this forum, hoping someone can make me understand this. [Please move this thread to the necessary section, if I posted it in a wrong section. Thanks in advance.] ----------------------------------- "Energy can neither be created nor destroyed." "A force of an attraction exists between any two objects that have mass. The more mass they have, the greater the force of attraction. The closer they are, the greater the force of attraction." The problem is... Let's say, there's an earth and a moon. The attraction force between them won't disappear any time soon, and so it will remain constant. However, the gravitational energy of moon acts on the tidal waves... Gravitational energy => Tidal energy The tidal energy is then converted to mechanical energy, which is converted to electrical energy. Tidal Energy => Mechanical Energy => Electrical Energy So in the end, we get an eletrical energy. However, we move that electrical energy to another planet, which is not the earth (or moon). We repeat this process multiple times. However, the attraction force between the Earth and Moon will still remain constant. And, we will always be able to convert the electrical energy from it. The energy source will never be depleted. Doesn't this mean that the energy can be created over the time? Or, am I wrong? Can anyone help me clarify it? Thank you.