Nice read @zyx066
In friction-less space however, the ball would just keep moving and wouldn't slow down.
There's something I must object to. There is no friction in space (at least in most parts, within gas and dust clouds it looks different), but there are the gravitational forces of stars, planets, galaxies, etc.. Masses can be deflected, accelerated and braked by gravity. So gravity in space should be something similar to what friction is on earth. Even if the strength of the force is not the same, it can have the same effects.
Please correct me if I'm wrong.
Greetz
Thanks for responding @astrophoto.kevin, I appreciate that very much :-)
And yes, you're right that space isn't totally devoid of friction and the friction between surfaces stays the same in space also. I cheated for simplicity's sake ;-) Even in "empty" space the vacuum isn't perfect, so even when the ball travels freely, the occasional collision with atoms will cause an exchange of momentum between the ball and the atoms, and if I remember correctly our international space station orbiting earth has to periodically fire it's engine for that reason.
But that doesn't change the story in any significant way: where kinetic energy is lost, some other type of energy is gained (like heat), keeping intact the law of conservation of energy and keeping intact our imaginary supercomputers ability to know every event in four-dimensional space.
You're not wrong: I cheated to not further complicate a principle that's hard enough by itself to wrap my mind around :-)
Thank you very much for your detailed answer @zyx066
That shouldn't be any criticism, I just wanted to say that :-)
You're right, the space station slows down due to this and the attraction of the Earth so that it has to ignite its propulsion every now and then to maintain its speed and due to this its orbit.
You see that just right. Energy cannot be lost. It can only be changed or transmitted.
I wouldn't say right now that you cheated. That would be much too hard. Rather concealed, but in the sense of simplicity. :-)
In any case: Keep up your work! :-)