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Comment by mrexroad | Hacker News Reader

I think most people would consider “falling” to be going “down” a gravity well. Stable orbits around a gravity well, or at sufficient distance to not be influenced by it, are not what most would consider to be “falling.”

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In the sense that matters for this discussion, zero g is the same as falling--both are weightless conditions. So the GP is correct and my original comment was in error; "zero g" can't be what is making the difference.

But that’s a misunderstanding. Stable orbits are free fall.

There is no such thing as a stable orbit “at sufficient distance to not be influenced by” gravity.

There’s no such thing as a sufficient distance.

I think more precisely, the traditional definition of an orbit (stable or not) is that it's influenced by gravity. You could be in a situation where the influence of gravity was negligible (say, far beyond any galaxy) but it wouldn't be considered an orbit at that point.

I guess certain multi-body situations like Lagrange points might make it debatable about which "direction" you're falling though.

I agree with mrexroad. Falling implies downward velocity. Free-fall is a different term that implies downward acceleration. For example, a ballistic projectile fired up that then falls back down first climbs, then falls, but it is in free-fall the whole time.

> Falling implies downward velocity. Free-fall is a different term that implies downward acceleration.

The GGP didn't say zero-g "is" falling. They said it's "the same as" falling. Which, for purposes of this discussion, it is, for the reason I gave--the key common property is being weightless, i.e., free falling.

Note, btw, that "free-fall" does not necessarily imply "downward acceleration". It just means "weightless". You could be weightless, in free fall, far out in deep space well away from all gravitating bodies, so that there is no well-defined notion of "downward acceleration" in your vicinity.

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