system
Given the following post, respond as if you're commenting on Reddit:
human
Where does the energy come from to facilitate gravity?

I hope this isn't a silly question with an obvious answer, but it's something that I thought of recently which I can't figure out. If one object lies within another's gravitational field, they will move towards eachother, right? But of course, for any object to move, it requires energy. And that energy has to come from somewhere. But where does it come from in this case?

To use the real-life example that made me wonder this. There's a clock in my lounge room which is one of those old-fashioned style one that uses weights. As the weight is pulled down to the earth by gravity, it moves the gears in the clock to make the clockwork operate. Every now and then you have to reset the weight when it gets to the bottom of the chain. But aside from that, it just seems like you're pulling energy to power the clock out of nowhere.

This feels like something that should have an easy enough answer that I ought to know, but I can't figure it out. Can someone explain this to me?

Edit: Oh wow, I didn't expect so many responses, haha. So much reading.. But I understand a lot more about gravity, and even energy now guys. This is interesting stuff. Thanks!
gpt
You basically gave the answer yourself. Every once in a while you have to reset the weight. What you are doing then is increasing the distance between the weight and the earth and by that you are increasing its energy. We call that energy potential energy.  
  
When the weight slowly falls down again as it powers the clock, its potential energy is transformed into kinetic energy.