I know this is an incredibly simple question, but I am trying to find a very simple explanation to this other than the simple logic that energy is conserved when two items impact and bounce off each other.
The question is this: how do particles, atoms, objects just carry on moving in space in their free will (in a "vacuum")? When I am throwing a ball and let go of it (imagining that myself and the ball are in a vacuum of which I am impervious) why does it keep pushing itself forward? I know there's a logic to it that says "what's there to stop it" but really, what is keeping it going, infinitely through a real vacuum?
So there's kinetic energy which is being used, and potential energy inside it. Is the kinetic energy flaring out the back of it like a ball shaped rocket? Is it really just the simple logic that "nothing is there to stop it"? Or could there be other methods such as propagation? With dark energy?
I know all the Newtonian stuff just to be straight, and I know about friction etc etc and the maths behind those. It's just the acceptance that things just carry on moving that I'm finding difficult.
Edit: just realised, okay, energy is not being used. So why is it just cruising?
Edit: I can't vote up yet by the way, else I would on all these great answers! Thanks everyone.