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Picture this if you can.
Deep space with nothing as we are told.
A so called solid ball has been moved somehow in it, very slowly.
So here's the way it appears to me.
The ball was somehow pushed which is now moving forever unless it hits something but for this thought we will stick to the space we're told.
Now here's the key and I'd like an explanation.
If that ball is moving in space it has to be moving in a direction at a constant velocity forever because as I am told, this is conservation of the momentum that was apparently applied to the ball to get it underway.
Yes, if there really were no others forces involved.
Anywhere in the solar system, however, there is gravitation from the sun, planets and any other nearby objects.
The sun is so massive that, unless your ball is close to a planet it would be mainly affected by the gravitation of tne sun and would end up in an orbit around the sun, though probably a very elliptic one.
Your ball would then continue in this orbit, except in the very unlikely event of it striking some object.
In space as we are told there is no up nor down nor direction for anything in it so how can any object move in it?
No gravity, no matter and no direction and yet we can have something not only be moved in it but carry on moving within it.
How?
Down is just a term indicating the direction things will fall or hang and up is the opposite direction.
But, that does not mean that there are no directions in space, just that we need a different way to measure it.
In space navigation direction can be determined by star sights, as was done on the Apollo missions.
There may be little or no gravitation and no matter but there are still directions and your ball could still travel.
Because if there's no real rational answer, there's no real meaning of conservation of momentum and also no inertia.
Of course there are rational answers!
The reason that idealised "laws" are useful is that it let's us determine what will happen in any given situation.
The deviations from the ideal situation (friction, air resistance etc) can then be allowed for.
Then when it comes to the motion of satellites in High Earth Orbit, "air" resistance is so low that it can usually be ignored.
You might call all this illogical. There's nothing I can do about that. I'm just doing my poor best to say it how it is.