Spent a moment thinking about this and I think there’s an implied definition for what “on earth” means that we intuitively accept but don’t ever really need to state.
If your projected free-fall trajectory both forward and backward in time intersects with the surface of the earth then you are “on earth”.
Standing on the ground? Intersects twice.
Thrown rock? Intersects twice.
Person in an airplane? Intersects twice.
ISS? No intersection.
Incoming impact meteor? One intersection.
The ISS was launched from Earth, in pieces but still it’s of Earth origin, and will eventually fall back to Earth. It’s inside the Earth’s atmosphere and experiences drag. It’s orbit has to be adjusted and maintained.
Yes, that’s all true, but none of that describes its free-fall trajectory. Drag causes it to deviate from free-fall very slightly, and it definitely wasn’t in free-fall when the pieces were launched from Earth
Spent a moment thinking about this and I think there’s an implied definition for what “on earth” means that we intuitively accept but don’t ever really need to state.
If your projected free-fall trajectory both forward and backward in time intersects with the surface of the earth then you are “on earth”.
Standing on the ground? Intersects twice. Thrown rock? Intersects twice. Person in an airplane? Intersects twice. ISS? No intersection. Incoming impact meteor? One intersection.
The ISS was launched from Earth, in pieces but still it’s of Earth origin, and will eventually fall back to Earth. It’s inside the Earth’s atmosphere and experiences drag. It’s orbit has to be adjusted and maintained.
Yes, that’s all true, but none of that describes its free-fall trajectory. Drag causes it to deviate from free-fall very slightly, and it definitely wasn’t in free-fall when the pieces were launched from Earth