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straight line vs. ellipsis: Galileo's and Leo's thought experiemnts

Galileo had thought experiments whose conclusion was that -- absent force -- a thing will move in a straight line without ever stopping.

Might it not be better to plug in the consideration of gravity to thought experiments about momentum.  And in such a case, wouldn't be end up thing of movement as naturally moving in an ellipsis?  I throw something in the air and it returns in an apparently parabolic path.  Well, maybe it's really a really small part of an ellipsis.  And that ellipsis is cut short by the fact that the projectile hit the earth.  But if the projectile had been flying in the same direction with respect to the center of the earth while the earth itself was thousands of times denser, then the earth's surface would be so much closer to the earth's center that the projectile would not end up hitting the earth at all.  Rather, it would fly in an ellipsis, like other satellites.  

One might object that we are better off abstracting from gravity.  But whatever it is that explains momentum might be inseparable from gravity--in which case Galileo's thought experiment is the type of abstraction that leads to untruth.

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